Phytonomy plant anatomy


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Phytonomy plant anatomy

  1. 1. Plant anatomyFrom Wikipedia, the free encyclopediaPlant anatomy or phytotomy is the general term for the study of the internal structure ofplants. While originally it included plant morphology, which is the description of thephysical form and external structure of plants, since the mid Twentieth Century theinvestigation of plant anatomy is considered a separate, distinct field, and refers to justthe internal plant structures.[1] Plant anatomy is now frequently investigated at the cellularlevel, and often involves the sectioning of tissues and microscopy.Contents • 1 Structural divisions • 2 History • 3 See also • 4 References • 5 External linksStructural divisionsPlant anatomy is sometimes divided into the following categories: Flower anatomy Calyx Corolla Androecium Gynoecium Leaf anatomy Leaf anatomy Stem anatomy Stem structure Fruit/Seed anatomy Ovule Seed structure Pericarp Accessory fruit Wood anatomy Bark Cork Phloem Vascular cambium Heartwood and sapwood branch collar Root anatomy Root structureHistoryAbout 300 BCE Theophrastus wrote a number of plant treatises, only two of whichsurvive. He developed concepts of plant morphology and classification, which did notwithstand the scientific scrutiny of the Renaissance.Plant anatomy, From Wikipedia, the free encyclopedia 1
  2. 2. A Swiss physician and botanist, Gaspard Bauhin, introduced binomial nomenclature intoplant taxonomy. He published Pinax theatri botanici in 1596, which was the first to usethis convention for naming of species. His criteria for classification included naturalrelationships, or affinities, which in many cases were structural.Italian doctor and microscopist, Marcello Malpighi, was one of the two founders of plantanatomy. In 1671 he published his Anatomia Plantarum, the first major advance in plantphysiogamy since Aristotle.The British doctor, Nehemiah Grew was one of the two founders of plant anatomy. Hepublished An Idea of a Philosophical History of Plants in 1672 and The Anatomy ofPlants in 1682. Grew is credited with the recognition of plant cells, although he calledthem vesicles and bladders. He correctly identified and described the sexual organs ofplants (flowers) and their parts.In the Eighteenth Century, Carolus Linnaeus established taxonomy based on structure,and his early work was with plant anatomy. While the exact structural level which is tobe considered to be scientifically valid for comparison and differentiation has changedwith the growth of knowledge, the basic principles were established by Linnaeus. Hepublished his master work, Species Plantarum in 1753.In 1802, French botanist, Charles-François Brisseau de Mirbel, published Traitédanatomie et de physiologie végétale (Treatise on Plant Anatomy and Physiology)establishing the beginnings of the science of plant cytology.In 1812, Johann Jacob Paul Moldenhawer published Beyträge zur Anatomie der Pflanzen,describing microscopic studies of plant tissues.In 1813 a Swiss botanist, Augustin Pyrame de Candolle, published Théorie élémentairede la botanique, in which he argued that plant anatomy, not physiology, ought to be thesole basis for plant classification. Using a scientific basis, he established structuralcriteria for defining and separating plant genera.In 1830, Franz Meyen published Phytotomie, the first comprehensive review of plantanatomy.In 1838 German botanist, Matthias Jakob Schleiden, published Contributions toPhytogenesis, stating, "the lower plants all consist of one cell, while the higher plants arecomposed of (many) individual cells" thus confirming and continuing Mirabels work.A German-Polish botanist, Eduard Strasburger, described the mitotic process in plantcells and further demonstrated that new cell nuclei can only arise from the division ofother pre-existing nuclei. His Studien über Protoplasma was published in 1876.Gottlieb Haberlandt, a German botanist, studied plant physiology and classified planttissue based upon function. On this basis, in 1884 he published PhysiologischePflanzenanatomie (Physiological Plant Anatomy) in which he described twelve types oftissue systems (absorptive, mechanical, photosynthetic, etc.).British paleobotanists Dunkinfield Henry Scott and William Crawford Williamsondescribed the structures of fossilized plants at the end of the Nineteenth Century. ScottsStudies in Fossil Botany was published in 1900.Following Charles Darwins Origin of Species a Canadian botanist, Edward CharlesJeffrey, who was studying the comparative anatomy and phylogeny of different vascularplant groups, applied the theory to plants using the form and structure of plants toestablish a number of evolutionary lines. He published his The Anatomy of Woody Plantsin 1917.Plant anatomy, From Wikipedia, the free encyclopedia 2
  3. 3. The growth of comparative plant anatomy was spearheaded by a British botanist, AgnesArber. She published Water Plants: A Study of Aquatic Angiosperms in 1920,Monocotyledons: A Morphological Study in 1925, and The Gramineae: A Study ofCereal, Bamboo and Grass in 1934.Following World War II, Katherine Esau published, Plant Anatomy (1953), whichbecame the definitive textbook on plant structure in North American universities andelsewhere, it was still in print as of 2006. She followed up with her Anatomy of seedplants in 1960.See also • Plant morphology • Plant physiologyReferences 1. ^ Raven, P. H., R. F. Evert, & S. E. Eichhorn. Biology of Plants, 7th ed., page 9. (New York: W. H. Freeman, 2005). ISBN 0-7167-1007-2. • Eames, Arthur Johnson and MacDaniels, Laurence H. (1947) An Introduction to Plant Anatomy McGraw-Hill, New York; • Esau, Katherine (1965) Plant Anatomy (2nd ed.) Wiley, New York;External links • Farabee, M.J. (2001) "Plants and their structure" Estrella Mountain Community College, Phoenix, Arizona • Botanical Visual GlossaryPlant morphologyPlant morphology (or phytomorphology) is the general term for the study of themorphology (physical form and external structure) of plants.[1] This is usually considereddistinct from plant anatomy, which is the study of the internal structure of plants,especially at the microscopic level. Plant morphology is useful in the identification ofplants.Inflorescences emerging from protective coveringsPlant anatomy, From Wikipedia, the free encyclopedia 3
  4. 4. Contents • 1 Scope • 2 A comparative science o 2.1 Homology o 2.2 Convergence • 3 Vegetative and reproductive characters o 3.1 Use in identification o 3.2 Alternation of generations • 4 Plant development o 4.1 Plant growth o 4.2 Morphological variation 4.2.1 Positional effects 4.2.2 Environmental effects 4.2.3 Juvenility • 5 See also • 6 References • 7 External linksScopePlant morphology "represents a study of the development, form, and structure of plants,and, by implication, an attempt to interpret these on the basis of similarity of plan andorigin."[2] There are four major areas of investigation in plant morphology, and eachoverlaps with another field of the biological sciences.First of all, morphology is comparative, meaning that the morphologist examinesstructures in many different plants of the same or different species, then drawscomparisons and formulates ideas about similarities. When structures in different speciesare believed to exist and develop as a result of common, inherited genetic pathways,those structures are termed homologous. For example, the leaves of pine, oak, andcabbage all look very different, but share certain basic structures and arrangement ofparts. The homology of leaves is an easy conclusion to make. The plant morphologistgoes further, and discovers that the spines of cactus also share the same basic structureand development as leaves in other plants, and therefore cactus spines are homologous toleaves as well. This aspect of plant morphology overlaps with the study of plant evolutionand paleobotany.Asclepia syriaca showing complex morphology of the flowers.Secondly, plant morphology observes both the vegetative (somatic) structures of plants,as well as the reproductive structures. The vegetative structures of vascular plantsincludes the study of the shoot system, composed of stems and leaves, as well as the rootPlant anatomy, From Wikipedia, the free encyclopedia 4
  5. 5. system. The reproductive structures are more varied, and are usually specific to aparticular group of plants, such as flowers and seeds, fern sori, and moss capsules. Thedetailed study of reproductive structures in plants led to the discovery of the alternationof generations found in all plants and most algae. This area of plant morphology overlapswith the study of biodiversity and plant systematics.Thirdly, plant morphology studies plant structure at a range of scales. At the smallestscales are ultrastructure, the general structural features of cells visible only with the aidof an electron microscope, and cytology, the study of cells using optical microscopy. Atthis scale, plant morphology overlaps with plant anatomy as a field of study. At thelargest scale is the study of plant growth habit, the overall architecture of a plant. Thepattern of branching in a tree will vary from species to species, as will the appearance ofa plant as a tree, herb, or grass.Fourthly, plant morphology examines the pattern of development, the process by whichstructures originate and mature as a plant grows. While animals produce all the bodyparts they will ever have from early in their life, plants constantly produce new tissuesand structures throughout their life. A living plant always has embryonic tissues. The wayin which new structures mature as they are produced may be affected by the point in theplants life when they begin to develop, as well as by the environment to which thestructures are exposed. A morphologist studies this process, the causes, and its result.This area of plant morphology overlaps with plant physiology and ecology.A comparative scienceA plant morphologist makes comparisons between structures in many different plants ofthe same or different species. Making such comparisons between similar structures indifferent plants tackles the question of why the structures are similar. It is quite likely thatsimilar underlying causes of genetics, physiology, or response to the environment haveled to this similarity in appearance. The result of scientific investigation into these causescan lead to one of two insights into the underlying biology: 1. Homology - the structure is similar between the two species because of shared ancestry and common genetics. 2. Convergence - the structure is similar between the two species because of independent adaptation to common environmental pressures.Understanding which characteristics and structures belong to each type is an importantpart of understanding plant evolution. The evolutionary biologist relies on the plantmorphologist to interpret structures, and in turn provides phylogenies of plantrelationships that may lead to new morphological insights.Homology Main article: Homology (biology)When structures in different species are believed to exist and develop as a result ofcommon, inherited genetic pathways, those structures are termed homologous. Forexample, the leaves of pine, oak, and cabbage all look very different, but share certainbasic structures and arrangement of parts. The homology of leaves is an easy conclusionto make. The plant morphologist goes further, and discovers that the spines of cactus alsoshare the same basic structure and development as leaves in other plants, and thereforecactus spines are homologous to leaves as well.Convergence Main article: Convergent evolutionPlant anatomy, From Wikipedia, the free encyclopedia 5
  6. 6. When structures in different species are believed to exist and develop as a result ofcommon adaptive responses to environmental pressure, those structures are termedconvergent. For example, the fronds of Bryopsis plumosa and stems of Asparagussetaceus both have the same feathery branching appearance, even though one is an algaand one is a flowering plant. The similarity in overall structure occurs independently as aresult of convergence. The growth form of many cacti and species of Euphorbia is verysimilar, even though they belong to widely distant families. The similarity results fromcommon solutions to the problem of surviving in a hot, dry environment.Euphorbia obesa, a spurgeAstrophytum asterias, a cactus.Vegetative and reproductive charactersPlant morphology treats both the vegetative structures of plants, as well as thereproductive structures.The vegetative (somatic) structures of vascular plants include two major organ systems:(1) a shoot system, composed of stems and leaves, and (2) a root system. These twosystems are common to nearly all vascular plants, and provide a unifying theme for thestudy of plant morphology.By contrast, the reproductive structures are varied, and are usually specific to aparticular group of plants. Structures such as flowers and fruits are only found in theangiosperms; sori are only found in ferns; and seed cones are only found in conifers andother gymnosperms. Reproductive characters are therefore regarded as more useful forthe classification of plants than vegetative characters.Use in identification Main article: Identification keyPlant biologists use morphological characters of plants which can be compared, measuredcounted and described to assess the differences or similarities in plant taxa and use thesecharacters for plant identification, classification and descriptions.When characters are used in descriptions or for identification they are called diagnosticor key characters which can be either qualitative and quantitative. 1. Quantitative characters are morphological features that can be counted or measured for example a plant species has flower petals 10-12 mm wide. 2. Qualitative characters are morphological features such as leaf shape, flower color or pubescence.Both kinds of characters can be very useful for the identification of plants.Alternation of generations Main article: Alternation of generationsThe detailed study of reproductive structures in plants led to the discovery of thealternation of generations, found in all plants and most algae, by the German botanistWilhelm Hofmeister. This discovery is one of the most important made in all of plantPlant anatomy, From Wikipedia, the free encyclopedia 6
  7. 7. morphology, since it provides a common basis for understanding the life cycle of allplants.Plant developmentProgressive sections of a stem, showing internal development and growth.[3]Plant development is the process by which structures originate and mature as a plantgrows. It is a subject studies in plant anatomy and plant physiology as well as plantmorphology.The process of development in plants is fundamentally different from that seen invertebrate animals. When an animal embryo begins to develop, it will very early produceall of the body parts that will ever have in its life. When the animal is born. or hatchesfrom its egg. it has all its body parts and from that point will only grow larger and moremature. By contrast, plants constantly produce new tissues and structures throughout theirlife from meristems located at the tips of organs, or between mature tissues. Thus, aliving plant always has embryonic tissues.The properties of organization seen in a plant are emergent properties which are morethan the sum of the individual parts. "The assembly of these tissues and functions into anintegrated multicellular organism yields not only the characteristics of the separate partsand processes but also quite a new set of characteristics which would not have beenpredictable on the basis of examination of the separate parts."[4] In other words, knowingeverything about the molecules in a plant are not enough to predict characteristics of thecells; and knowing all the properties of the cells will not predict all the properties of aplants structure.Plant growth Further information: Meristem, Cellular differentiation, Morphogenesis, and Plant embryogenesisA vascular plant begins from a single celled zygote, formed by fertilisation of an egg cellby a sperm cell. From that point, it begins to divide to form a plant embryo through theprocess of embryogenesis. As this happens, the resulting cells will organize so that oneend becomes the first root, while the other end forms the tip of the shoot. In seed plants,Plant anatomy, From Wikipedia, the free encyclopedia 7
  8. 8. the embryo will develop one or more "seed leaves" (cotyledons). By the end ofembryogenesis, the young plant will have all the parts necessary to begin in its life.Once the embryo germinates from its seed or parent plant, it begins to produce additionalorgans (leaves, stems, and roots) through the process of organogenesis. New roots growfrom root meristems located at the tip of the root, and new stems and leaves grow fromshoot meristems located at the tip of the shoot. Branching occurs when small clumps ofcells left behind by the meristem, and which have not yet undergone cellulardifferentiation to form a specialized tissue, begin to grow as the tip of a new root orshoot. Growth from any such meristem at the tip of a root or shoot is termed primarygrowth and results in the lengthening of that root or shoot. Secondary growth results inwidening of a root or shoot from divisions of cells in a cambium.In addition to growth by cell division, a plant may grow through cell elongation. Thisoccurs when individual cells or groups of cells grow longer. Not all plant cells will growto the same length. When cells on one side of a stem grow longer and faster than cells onthe other side, the stem will bend to the side of the slower growing cells as a result.Morphological variationPlants exhibit natural variation in their form and structure. While all organisms vary fromindividual to individual, plants exhibit an additional type of variation. Within a singleindividual, parts are repeated which may differ in form and structure from other similarparts. This variation is most easily seen in the leaves of a plant, though other organs suchas stems and flowers may show similar variation. There are three primary causes of thisvariation: positional effects, environmental effects, and juvenility.Positional effectsVariation in leaves from the giant ragweed illustrating positional effects. The lobedleaves come from the base of the plant, while the unlobed leaves come from the top of theplant.Although plants produce numerous copies of the same organ during their lives, not allcopies of a particular organ will be identical. There is variation among the parts of amature plant resulting from the relative position where the organ is produced. Forexample, along a new branch the leaves may vary in a consistent pattern along thebranch. The form of leaves produced near the base of the branch will differ from leavesproduced at the tip of the plant, and this difference is consistent from branch to branch ona given plant and in a given species. This difference persists after the leaves at both endsof the branch have matured, and is not the result of some leaves being younger thanothers.Environmental effectsThe way in which new structures mature as they are produced may be affected by thepoint in the plants life when they begin to develop, as well as by the environment towhich the structures are exposed. This can be seen in aquatic plants and emergent plants.Plant anatomy, From Wikipedia, the free encyclopedia 8
  9. 9. JuvenilityJuvenility in a seedling of European beech. Notice the difference in shape between thefirst dark green "seed leaves and the lighter second pair of leaves.The organs and tissues produced by a young plant, such as a seedling, are often differentfrom those that produced by the same plant when it is older. This phenomenon is knownas juvenility. For example, young trees will produce longer, leaner branches that growupwards more than the branches they will produce as a fully grown tree. In addition,leaves produced during early growth tend to be larger, thinner, and more irregular thanleaves on the adult plant. Species of juvenile plants may look so completely differentfrom the adult leaves that egg-laying insects do not recognize the plant as food for theiryoung.See also • List of plant morphology terms • Plant anatomy • Plant physiology • Plant evolutionary developmental biologyReferences 1. ^ Raven, P. H., R. F. Evert, & S. E. Eichhorn. Biology of Plants, 7th ed., page 9. (New York: W. H. Freeman, 2005). ISBN 0-7167-1007-2. 2. ^ Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. Morphology of Plants and Fungi, 5th ed., page 3. (New York: Harper-Collins, 1987). ISBN 0-06-040838-1. 3. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1] 4. ^ Leopold, A. C. Plant Growth and Development, page 183. (New York: McGraw-Hill, 1964).External links • Botanical Visual GlossaryPlant anatomy, From Wikipedia, the free encyclopedia 9
  10. 10. List of plant morphology termsJump to: navigation, search It has been suggested that Glossary of botanical terms be merged into this article or section. (Discuss)Biologists that study plant morphology use a number of different terms to describe plantorgans and parts that can be observed with the human eye using no more than a hand heldmagnifying lens. These terms are used to identify and classify plants.Contents1 General plant terms o 1.1 Plant habit o 1.2 Duration • 2 Vegetative morphology o 2.1 Roots o 2.2 Stems o 2.3 Buds o 2.4 Leaves • 3 Epidermis and periderm texture • 4 Floral morphology o 4.1 Basic flower parts o 4.2 Inflorescences o 4.3 Insertion of floral parts • 5 Specialized terms o 5.1 Union of flower parts o 5.2 Flower sexuality and presence of floral parts o 5.3 Flower symmetry • 6 Pollination and fertilization o 6.1 Embryo development • 7 Fruits and seeds o 7.1 Terms for fruits o 7.2 Fruit types • 8 Seedless reproduction o 8.1 Pteridophyte sporangium terms o 8.2 Bryophyte gametangium terms o 8.3 Bryophyte sporangium terms • 9 See also • 10 ReferencesGeneral plant terms • Abaxial - located on the side away from the axis. • Wing - any flat surfaced structure emerging from the side or summit of an organ; seeds, stems.Plant habit • Acaulescent - the leaves and inflorescence rise from the ground, appearing to have no stem.Plant anatomy, From Wikipedia, the free encyclopedia 10
  11. 11. • Acid plant - plants with acid saps, normally due to the production of ammonium salts (malic and oxalic acid) • Acme - the period when the plant or population is at its maximum vigor. • Actinomorphic - parts of plants that are radially symmetrical in arrangement. • Arborescent - growing into a tree-like habit, normally with a single woody stem. • Ascending - growing uprightly, in an upward direction, heading in the direction of the top. • Assurgent - growth ascending. • Branching - dividing into multiple smaller segments. • Caducous - falling away early. • Caulescent - with a well developed stem above ground. • Cespitose - forming dense tufts, normally applied to small plants typically growing into mats, tufts or clumps. • Creeping - growing along the ground and producing roots at intervals along surface. • Deciduous - falling away after its function is completed. • Decumbent - growth starts off prostrate and the ends become upright. • Deflexed - bending downward. • Determinate growth - Growing for a limited time, floral formation and leaves. • Dimorphic - of two different forms. • Ecad - a plant assumed to be adapted to a specific habitat. • Ecotone - the boundary that separates two plant communities, generally of major rank - trees in woods and grasses in savanna for example. • Ectogenesis - variation in plants due to conditions out side of the plants. • Ectoparasite - a parasitic plant that has most of its mass outside of the host, the body and reproductive organs of the plant lives outside of the host. • Epigeal - living on the surface of the ground. See also terms for seeds. o Epigean - occurring on the ground. o Epigeic - plants with stolons on the surface of the ground. o Epigeous - on the ground. Used for leaf fungus that live on the surface of the leaf. • Epilithic - growing on the surface of rocks. • Epiphloedal - growing on the bark of trees. o Epiphloedic - an organism that grows on the bark of trees. • Epiphyllous - growing on the leaves. For example, Helwingia japonica has epiphyllous flowers (ones that form on the leaves).[1] • Epiphyte - growing on another organism but not parasitic. Not growing on the ground. o Epiphytic - having the nature of an epiphyte. • Equinoctial - a plants that has flowers that open and close at definite times during the day. • Erect - having an essentially upright vertical habit or position. • Escape - plant originally under cultivation that has become wild, garden plant growing in natural areas. • Evergreen - remaining green in the winter or during the normal dormancy period for other plants.Plant anatomy, From Wikipedia, the free encyclopedia 11
  12. 12. • Eupotamous - living in rivers and streams. • Euryhaline - normally living in salt water but tolerant of variable salinity rates. • Eurythermous - tolerant of a wide range of temperature. • Exclusive species - confined to specific location. • Exotic - not native to the area or region. • Exsiccatus - a dried plant, most often used for specimens in a herbarium. • Lax - non upright, growth not strictly upright or hangs down from the point of origin. • Parasitic - using another plant as a source of nourishment. • Precocious - flowering before the leaves emerge. • Procumbent - growing prostrate or trailing but not rooting at the nodes. • Prostrate - laying flat on the ground, stems or even flowers in some species. • Repent - creeping. • Rosette - cluster of leaves with very short internodes that are crowded together, normally on the soil surface but sometimes higher on the stem. o Rostellate - like a rosette. o Rosulate - arranged into a rosette. • Runner - an elongated, slender branch that roots at the nodes or tip. • Stolon - A branch that forms near the base of the plant and grows horizontally and roots and produces new plants at the nodes or apex. o Stoloniferous - plants produce stolons. • Semi-erect - • Suffrutescent - somewhat shrubby, or shrubby at the base. • Upright - • Virgate - wand-like, slender erect growing stem with many leaves or very short branches. • Woody - forming secondary growth laterally around the plant so as to form wood.DurationDuration of individual plant lives are described using these terms: • Annual - plants that live, reproduce and die in one growing season. • Biennial - plants that need two growing seasons to complete their life cycle, normally vegetative growth the first year and flowering the second year. • Herbs - see herbaceous. • Herbaceous - plants with shoot systems that die back to ground each year- both annual and non-woody perennial plants. • Herbaceous perennial - non-woody plants that live for more than two years and the shoot system dies back to the soil level each year. • Woody perennial - true shrubs and trees or some vines with shoot systems that remain alive above the soil surface from one year to the next. • Monocarpic - plants that live for a number of years then after flowering and seed set die.Vegetative morphology • Vernation - the arrangement of leaves, petals or sepals in an unopened bud.Plant anatomy, From Wikipedia, the free encyclopedia 12
  13. 13. RootsRoots generally do not offer many characters used in plant identification andclassification but are important in determining plant duration though in some groups theyvery important for proper identification including the grasses. • Adventitious - roots that form from other than the hypocotyl or from another roots. Roots forming on the stem are adventitious. • Aerial - roots growing in the air. • Crown - the place where the roots and stem meet, which may or may not be clearly visible.[2] • Fibrous - roots are thread-like and normally tough. • Fleshy - roots are relatively thick and soft, normally made up of storage tissue. Roots are typical long and thick but not thickly rounded in shape. • Haustorial - specialized roots that invade other plants and absorb nutrients from those plants. • Lignotuber - root tissue that allows plants to regenerate after fire or other damage. • Primary - roots that develops from the radically of the embryo, normally the first root to emerge from the seed as it germinates. • Root Hairs - very small, often one cell wide, roots that do most of the water and nutrient absorption. • Secondary - roots forming off of the primary root, often called branch roots. • Tap - a primary root that more or less enlarges and grows downward into the soil. • Tuberous - roots that are thick and soft, with storage tissue. Typically thick round in shape.Stems • Accessory buds - • Acrocarpous - produced at the end of a branch. • Acutangular - a stem that has several longitudinally running ridges with sharp edges. • Adventitious buds - • Alternate - buds are staggered on opposite sides of the branch • Accessory buds - • Bark - the outer layers of woody plants; cork, phloem, and vascular cambium. • Branches - • Bud - an immature stem tip, typically an embryonic shoot, ether producing a stem, leaves or flowers. • Bulb - an underground stem normally with a short basal surface and with thick fleshy leaves. • Bundle scar - • Caudex - the hard base produced by herbaceous perennials used to overwinter the plant. • Caulescent - with a distinctive stem. • Cladode - • Cladophyll - a flattened stem that is leaf-like and green- used for photosynthesis, normally plants have no or greatly reduced leaves. • Climbing - typically long stems, that cling to other objects.Plant anatomy, From Wikipedia, the free encyclopedia 13
  14. 14. • Corm - a compact, upright orientated stem that is bulb-like with hard or fleshy texture and normally covered with papery, thin dry leaves. Most often produced under the soil surface. • Cuticle - a waxy membrane covering some leaves and roots that is water-tight. • Decumbent - stems that lay on the ground but have the ends turning upward. • Dormant - a state of no growth or reduced growth • Early wood - • Epidermis - a layer of cells that cover all primary tissue separating them from the outside environment. • Erect - growing upright. • Flower bud - • Fruticose - woody stemmed with a shrub-like habit. Branching near the soil with woody based stems. • Guard cell - • Herbaceous - non-woody and dying to the ground at the end of the growing season. Annual plants die, while perennials regrow from from parts on the soil surface or below ground the next growing season. • Heartwood - • Latent buds - • Lenticel - • Internode - spaces between the nodes. • Late wood - • Lateral bud - • Leaf axils - the space created between a leaf and its branch. This is especially pronounced on monocots like bromeliads. • Leaf bud - • Leaf scar - the mark left on a branch from the previous location of a bud or leaf. • Lenticels - lens-shaped or warty patches of parenchymatous tissue on the surface of the stem. • Node - were leaves and buds are attached to the stem. • Pith - the spongy tissue at the center of a stem. o Chambered pith - o Continuous pith - o Diaphragmed pith - • Spine - an adapted leaf that is usually hard and sharp and is used for protection, and occasionally shading of the plant • Prickle - an extension of the cortex and epidermis that ends with a sharp point. • Prostrate - growing flat on the soil surface. • Rhizome - A horizontally orientated, prostrate stem with reduced scale-like leaves, normally growing under ground but also at the soil surface. Also produced by some species that grow in trees or water. • Rootstock - the underground part of a plant normally referring to a caudex or rhizome. • Runner - an above ground stem usually rooting and producing new plants at the nodes. • Scandent - a stem that climbs.Plant anatomy, From Wikipedia, the free encyclopedia 14
  15. 15. • Stolon - a horizontally growing stem similar to a rhizome, but growing above or along the ground. • Tendril - a thigmotropic organ which attached a climbing plant to a support o Leaf - the photosynthetic organ of a plant o Stem - vascular tissue that provides support for the plant • Terminal - • Terminal scale bud scar - • Thorn - • Tiller - • Tuber - • Twigs - • Opposite - buds are arranged in pairs on opposite sides of the branch • Pith - • Pore - • Rhizome - • Sapwood - • Stoma - • Vascular bundles - • Verticil - a whorl of leaves or flowers. o Verticillate - arranged in whorls. • Whorled - said of a collection of three or more leaves or flowers that arise from the same point.Buds • Accessory - • Adventitious - • Axillary - • Dormant - • Flower bud - • Lateral - • Leaf bud - • Mixed - buds that have both embryonic flowers and leaves. • Naked - • Pseudoterminal - • Reproductive - buds with embryonic flowers. • Scaly - • Terminal - bud at the tip or end of the stem. • Vegetative - buds containing embryonic leaves.LeavesLeaf Parts: - A complete leaf is composed of a blade, petiole and stipules and in manyplants one or more might be lacking or highly modified. • Blade - • Petiole - • Stipules - a pair of outgrowths from the base of the leaf petiole. • Stipuloid - resembling stipules.Duration of leaves: • Deciduous -Plant anatomy, From Wikipedia, the free encyclopedia 15
  16. 16. • Evergreen - • Fugacious - • Marcescent - • Persistent -Venation: • Acrodramous - when the veins run parallel to the leaf edge and fuse at the leaf tip. • Actinodromous - when the main veins of a leaf radiate from the tip of the petiole. • Vein - the externally visible vascular bundles, found on leafs, petals and other parts. • Veinlet - a small vein.Leaf Arrangement or Phyllotaxy: • Whorl - three or more leaves or branches or pedicels arising from the same node.Leaf Type: • Abruptly pinnate - a compound leaf without a terminal leaflet.Leaf Blade Shape: Main article: Leaf shape • Acicular (acicularis): Slender and pointed, needle-like • Acuminate (acuminata): Tapering to a long point • Aristate (aristata): Ending in a stiff, bristle-like point • Bipinnate (bipinnata): Each leaflet also pinnate • Cordate (cordata): Heart-shaped, stem attaches to cleft • Cuneate (cuneata): Triangular, stem attaches to point • Deltoid (deltoidea): Triangular, stem attaches to side • Digitate (digitata): Divided into finger-like lobes • Elliptic (elliptica): Oval, with a short or no point • Falcate (falcata): sickle-shaped • Flabellate (flabellata): Semi-circular, or fan-like • Hastate (hastata): shaped like a spear point, with flaring pointed lobes at the base • Lance-shaped, lanceolate (lanceolata): Long, wider in the middle • Linear (linearis): Long and very narrow • Lobed (lobata): With several points • Obcordate (obcordata): Heart-shaped, stem attaches to tapering point • Oblanceolate (oblanceolata): Top wider than bottom • Oblong (oblongus): Having an elongated form with slightly parallel sides • Obovate (obovata): Teardrop-shaped, stem attaches to tapering point • Obtuse (obtusus): With a blunt tip • Orbicular (orbicularis): Circular • Ovate (ovata): Oval, egg-shaped, with a tapering point • Palmate (palmata): Divided into many lobes • Pedate (pedata): Palmate, with cleft lobes • Peltate (peltata): Rounded, stem underneath • Perfoliate (perfoliata): Stem through the leaves • Pinnate (pinnata): Two rows of leaflets o odd-pinnate : pinnate with a terminal leaflet o paripinnate, even-pinnate : pinnate lacking a terminal leaflet • Pinnatisect (pinnatifida): Cut, but not to the midrib (it would be pinnate then)Plant anatomy, From Wikipedia, the free encyclopedia 16
  17. 17. • Reniform (reniformis): Kidney-shaped • Rhomboid (rhomboidalis): Diamond-shaped • Round (rotundifolia): Circular • Sagittate (sagittata): Arrowhead-shaped • Spatulate, spathulate (spathulata): Spoon-shaped • Spear-shaped (hastata): Pointed, with barbs • Subulate (subulata): Awl-shaped with a tapering point • Sword-shaped (ensiformis): Long, thin, pointed • Trifoliate, ternate (trifoliata): Divided into three leaflets • Tripinnate (tripinnata): Pinnately compound in which each leaflet is itself bipinnate • Truncate (truncata): With a squared off end • Unifoliate (unifoliata): with a single leafLeaf Base Shape: • Semiamplexicaul - the leaf base wraps around the stem, but not completely.Leaf Blade Apex: • Acuminate - narrowing to a point, used for other structures too. • Acute - with a sharp rather abrupt ending point. o Acutifolius - with acute leaves. • Attenuate - tapering gradually to a narrow end.Leaf Blade Margins: • Crenulate - with shallow, small rounded teeth.Leaf Modifications:Epidermis and periderm texture • Acanceous - being prickly. • Acantha - a prickle or spine. • Acanthocarpus - fruits are spiny. • Acanthocladous - the branches are spiny. • Aculeate - having a covering of prickles or needle-like growth. o Aculeolate - having spine-like processes. • Aden - a gland. o Adenoid - gland like. o Adenophore - a stalk that supports a gland. o Adenophyllous - leaves with glands. • Arachnoid - having a cobwebby appearance with entangled hairs. • Bloom - the waxy coating that covers some plants. • Canescent - with gray pubescence. • Ciliate - with a fringe of marginal hairs. • Coriaceouse - with a tough or leathery texture. • Fimbriate - finely cut into fringes, the edge of a frilly petal or leaf. • Floccose - • Glabrate - • Glabrous - smooth without any pubescences at all. • Glandular - • Glandular-punctate - covered across the surface with glands. • Hirsute - with long shaggy hairs, often stiff or bristly to the touch.Plant anatomy, From Wikipedia, the free encyclopedia 17
  18. 18. • Lanate - with woolly hairs. Thick wool like hairs. • Verrucose - with a wart surface, with low rounded bumps. • Villose - covered with fine long hairs that are not matted. o Villosity - villous indument.Floral morphology • Accrescent - Growing larger after anthesis, normally used for the calyx. • Anthesis - the period when the flower is fully open and functional.Basic flower parts • Acephalous - without a head, used for flower styles without a well-developed stigma. • Androecium - the stamens collectively. o Basifixed - attached by the base. o Connective - the part of the stamen joining the anther cells. o Diadelphous - o Didynamous - o Epipetalous - born on the corolla, often used in reference to stamens attached to the corolla. o Exserted - sticking out past the corolla, the stamens protrude past the margin of the corolla lip. o Extrose - opening towards the outside of the flower. o Gynandrium - combined male & female structure o Gynostregium - o Included - o Introrse - opening on the inside of the corolla, the stamens are contained within the margins of the petals. o Monodelphous - stamen filaments united into a tube. o Poricidal - anthers opening by terminal pores. o Staminode - a sterile stamen. Staminodial - flowers with sterile stamen. o Synanthamous - o Syngenesious - the anthers are united into a tube, the filaments are free. o Tetradynamous - o Translator - a structure uniting the pollinia in Asclepiadaceae and Orchidaceae. o Trinucleate - pollen containing three nuclei when shed. o Valvular - anthers opening by valves or small flaps, e.g. Berberis. o Versatile - anthers pivoting freely on the filament. • Anther - The distal end of the stamen where pollen is produced, normally composed of two parts called anther-sacs and pollen-sacs (thecae). • Bract - The leaf-like or scale-like leafy appendages that are located just below a flower, a flower stalk, or an inflorescence; they usually are reduced in size and sometimes showy or brightly colored.Plant anatomy, From Wikipedia, the free encyclopedia 18
  19. 19. • Calyx -The whorl of sepals at the base of a flower. • Carpel -The ovule-producing reproductive organ of a flower, consisting of the stigma, style and ovary. • Corolla -The whorl of petals of a flower. • Disk - an enlargement or outgrowth from the receptacle of the flower, located at the center of the flower of various plants. The term is also use as the central area of the head in composites were the tubular flowers are attached. • Filament - The stalk of a stamen • Floral axis - • Floral envelope - • Flower - • Fruit - a structure contain all the seeds produced by a single flower. • Gynoecium - The whorl of carpels. May comprise one (syncarpous) or more (apocarpous) pistils. Each pistil consists of an ovary, style and stigma (female reproductive organs of the flower). o Apocarpus - The gynoecium comprises more than one pistil. o Cell - o Compound pistil - o Funicle - the stalk that connects the ovule to the placenta. o Funiculus - o Loculus - the cavities located with in a carpel, ovary or anther. o Locule - o multicarpellate - o Placentra - o Placentation - Axile - Basal - Free-central - Pariental - o Septum - o Simple pistil - o Syncarpous - The gynoecium comprises one pistil. o Unicarpellate - • Hypanthium - • Nectar - a fluid produce by nectaries high in sugar content, used to attract pollinators. • Nectary - a gland that secrets nectar, most often found in flowers but also produced on other parts of plants too. • Nectar disk - when the floral disk contains nectar secreting glands, often modified as its main function in some flowers. • Ovary - • Ovules - • Pedicel - the stem or stalk that holds a single flower in an inflorescence. • Peduncle - The part of a stem that bears the entire inflorescence, normally having no leaves or the leaves are reduce to bracts. When the flower is solitary, it is the stem or stalk holding the flower.Plant anatomy, From Wikipedia, the free encyclopedia 19
  20. 20. o Peduncular - referring to or having a peduncle. o Pedunculate - having a peduncle. • Perianth - o Achlamydeous - without a perianth. • Petal - • Pistil - • Pollen - • Rachis - • Receptacle - the end of the pedicel that joins to the flower were the different parts of the flower are joined together, also called the torus. In Asteraceae the top of the pedicel upon which the flowers are joined. • Seed - • Sepal - • Stamen - • Staminode - • Stigma - • Style - • Tepal -Inflorescences • Capitulum - the flowers are arranged into a head composed of many separate unstalked flowers, the single flowers are called florets and are packed close together. The typical arrangement of flowers in the Asteraceae. • Compound Umbel - is an umbel where each stalk of the main umbel produces another smaller umbel of flowers. • Corymb - a grouping of flowers where all the flowers are at the same level, the flower stalks of different lengths forming a flat-topped flower cluster. • Cyme - is a cluster of flowers were the end of each growing point produces a flower. New growth comes from side shoots and the oldest and first flowers to bloom are at the top. • Single - one flower per stem or the flowers are greatly spread-apart as to appear they do not arise from the same branch. • Spike - when flowers arising from the main stem are without individual flower stalks. The flowers attach directly to the stem. • Solitary - same as single, with one flower per stem. • Raceme - is a flower spike with flowers that have stalks of equal length. The stem tip continues to grow and produce more flowers with the bottom flowers open first and blooming progresses up the stem. • Panicle - is a raceme with branches and each branch having a smaller raceme of flowers. The terminal bud of each branch continues to grow, producing more side shoots and flowers. • Pedicel - stem holding a one flower in an inflorescences. • Peduncle - stem holding an inflorescences, or a single flower. • Umbel - were the flower head has all the flower stalks rising from the same point of the same length, the flower head is rounded like an umbrella or almost circular.Plant anatomy, From Wikipedia, the free encyclopedia 20
  21. 21. • Verticillaster - a whorled collection of flowers around the stem, the flowers produced in rings at intervals up the stem. As the stem tip continues to grow more whorls of flowers are produced. Typical in Lamiaceae. o Verticil - flowers arranged in whorls at the nodes.Insertion of floral parts • Epigynous - • Half-inferior - • Hypogynous - • Inferior - • Insertion - o Stamens - o Ovary - • Perigynous - • Superior -Specialized terms • Wing - term used for the lateral petals of the flowers on species in Fabaceae and Polygalaceae. • Valvate - meeting along the margins but not overlapping.Union of flower parts • Adelphous - the androecium with the stamen filaments partly or completely fused together.Flower sexuality and presence of floral parts • Achlamydeous - flower without a perianth. • Apetalous - a flower without petals. • Accrescent - said of the calyx when it is persistent and enlarges as the fruit grows and ripens, applied to other structure sometimes. • Androgymous - used for the inflorescence of Carex when a spike has both staminate and pistillate flowers - the pistillate flowers are normally at the base of the spike. • Bisexual - • Complete - • Imperfect - • Naked -Flower symmetry • Actinomorphic - having a radial symmetry, as in regular flowers. o Actinomorphy - when the flower parts are arranged with radial symmetry. • Dialypetalae - • Incomplete - • Perfect - • Radial - • Unisexual - • Zygomorphic - one axis of symmetry running down the middle of the flower so the right and left halves reflect each other.Plant anatomy, From Wikipedia, the free encyclopedia 21
  22. 22. o Zygomorphy - the type of symmetry that most irregular flowers have with the upper half of the flower unlike the lower half. the left and right halves tend to be mirror images of each other.Pollination and fertilization • Allogamy – cross pollination, when one plant pollinates another plant • Anemophilous – wind pollinated. • Autogamy – self-pollination, when the flowers of the same plant pollinate flowers on the same plant or themselves. • Cantharophilous – beetle pollinated • Chiropterophilous - bat pollinated. • Cleistogamous – self-pollination of a flower that does not open. • Dichogamy – Flowers that cannot pollinate themselves because pollen is produced at a time when the stigmas are not receptive of pollen. • Entomophilous – insect pollinated. • Hydrophilous – Water pollinated, pollen is moved in water from one flower to the next. • Malacophilous – pollinated by snails and slugs. • Ornithophilous – pollinated by birds. • Pollination – the movement of pollen from the anther to the stigma. • Protandrous – when pollen is produced and shed before the carpels are mature. • Progynous – when the carpels mature before the stamens produce pollen.Embryo development • Antipodal cell - • Chalazal - • Coleoptile - • Coleorhiza - • Cotyledon - • Double ferilization - • Embryo – • Embryo sac - • Endosperm – • Filiform apparatus - • Germination – • Plumule - • Polar nuclei - • Radicle - • Scutellum - • Synergid - • Tegmen - • Testa - • Triploid - • Xenia - • Zygote –Plant anatomy, From Wikipedia, the free encyclopedia 22
  23. 23. Fruits and seedsFruits are the matured ovary of seed bearing plants and they include the contents of theovary, which can be floral parts like the receptacle, involucre, calyx and others that arefused to it. Fruits are often used to identify plant taxa and help to place the species in thecorrect family or differentiate different groups with in the same family.Terms for fruits • Accessory structures - parts of fruits that do not form from the ovary. • Beak - normally the slender elongated end of a fruit, typically a persistent style- base. • Circumscissile - a type of fruit dehiscences were the top of the fruit falls away like a lid or covering. • Dehiscent - the way a fruit openings and releases its contents, normally in a regular and distinctive fashion. • Endocarp - includes the wall of the seed chamber, the inner part of the pericarp. • Exocarp - the pericarps outer part. • Fleshy - soft and juicy. • Indehiscent - fruits that do not have specialized structures for opening and releasing the seeds, they remain closed after the seeds ripen and are opened by animals, weathering, fire or other external means. • Mesocarp - the middle layer of the pericarp. • Pericarp - the body of the fruit from its outside surface to the chamber were the seeds are, including the outside skin of the fruit and the inside lining of the seed chamber. • Suture - the seam along which the fruit opens, normally in most fruits it is were the carpel or carpels are fused together. • Valve - one of the segments of the capsule.Fruit typesFruits are divided into different types depending on how they form, were or how theyopen and what parts they are composed of. • Achaenocarp - see achene. • Achene - dry indehiscent fruit, they have one seed and form from a single carpel, the seed is distinct from the fruit wall. • Drupe - outer fleshy part surrounds a shell with a seed inside. • Utricle - a small inflated fruit with one seed that has thin walls,Seedless reproductionPteridophyte sporangium terms • Acrostichoid sorus - having several fused sori. • Annulus -outer part of sporangium • Elater - • Indusium - • Marginal - • Peltate - • Reniform - • Sporophyll - • Sorus / Sori -Plant anatomy, From Wikipedia, the free encyclopedia 23
  24. 24. • Strobilus - • Submarginal -Bryophyte gametangium terms • Acrandrous - used for moss species that have antheridia at the top of the stem. • Acrocarpous - In mosses, bearing the sporophyte at the axix of the main shoot • Acrogynous - In liverworts, the female sex organs terminate the main shoot • Anacrogynous - In liverworts, female sex organs are produced by a lateral cell, thus the growth of the main shoot is indeterminate • Androcyte - • Androecium - • Androgynous - Monoicous, and producing both types of sex organs together. • Antheridiophore - A specialised branch that bears the antheridia in the Marchantiales • Antherozoid - • Archegoniophore - A specialised branch that bears the archaegonia in the Marchantiales • Autoicous - Produces male and female sex organs on the same plant but on separate inflorescences • Bract - • Cladautoicous - Male and female inflorescences on separate branches of the same plant • Dioicous - Having two forms of gametophyte, one form bearing antheridia and one form bearing archegonia. • Gonioautoicous - Male is bud-like in the axil of a female branch • Inflorescence - • Involucre - A tube of thallus tissue that protects the archegonia • Monoicous - Having a single form of gametophyte bearing both antheridia and archegonia, either together or on separate branches. • Paraphyses - Sterile hairs surrounding the archegonia and antheridia • Perianth - A protective tube that surrounds the archegonia, characterises the Jungermannialean liverworts • Perichaetium - The cluster of leaves with the enclosed female sex organs • Perigonium - The cluster of leaves with the enclosed male sex organs • Pseudautoicous - Dwarf male plants growing on living leaves of female plants • Pseudomonoicous - • Pseudoperianth - An involucre that resembles a perianth, but is made of thallus tissue, and usually forms after the sporophyte develops • Rhizautoicous - Male inflorescence attached to the female stem by rhizoids • Synoicous - Male and female sex organs on the same gametophyte but are not clusteredBryophyte sporangium terms • Amphithecium - • Anisosporous - • Annulus - in mosses, cells with thick walls along the rim of the sporangium and were the peristome teeth are attached. • Apophysis -Plant anatomy, From Wikipedia, the free encyclopedia 24
  25. 25. • Archesporium - • Arthrodontous - • Articulate - • Astomous - • Basal membrane - • Calyptra - • Capsule - • Cleistocarpous - • Columella - • Dehisce - • Diplolepidous - • Divisural line - • Elater - • Endostome - • Endothecium - • Epiphragm - • Exostome - • Exothecium - • Foot - • Gymnostomous - • Haplolepidous - • Haustorium - • Hypophysis - • Immersed - • Indehiscent - • Inoperculate - • Nematodontous - • Nurse cells - • Operculate - • Operculum - • Oral - • Peristome - • Pseudoelater - • Seta - • Sporangium - • Stegocarpous - • Stoma - • Suboral - • Tapetum - • Trabecula - • Valve -See also • Glossary of botanical termsReferences 1. ^ Comparative morphology 2. ^ "glossary". Fire Effects Information System.Plant anatomy, From Wikipedia, the free encyclopedia 25
  26. 26. Sources • Jones, Samuel B., and Arlene E. Luchsinger. 1979. Plant systematics. McGraw- Hill series in organismic biology. New York: McGraw-Hill. • Usher, George, and George Usher. 1996. The Wordsworth dictionary of botany. Ware, Hertfordshire: Wordsworth Reference.Retrieved from ""Plant evolutionary developmental biologyPlant anatomy, From Wikipedia, the free encyclopedia 26
  27. 27. For a more ecological discussion on the evolution of plant morphology, refer toEvolutionary history of plantsEvolutionary developmental biology (evo-devo) refers to the study of developmentalprograms and patterns from an evolutionary perspective.[1] It seeks to understand thevarious influences shaping the form and nature of life on the planet. Evo-devo arose as aseparate branch of science only in the last decade.[2] Most of the synthesis in evo-devohas been in the field of animal evolution, one reason being the presence of elegant modelsystems like Drosophila, C.elegans, Zebrafish and Xenopus. However, in the past coupleof decades, a wealth of information on plant morphology, coupled with modernmolecular techniques has helped shed light on the conserved and unique developmentalpatterns in the plant kingdom also.Contents • 1 Historical perspective o 1.1 Before 1900 o 1.2 1900 to the present • 2 Organisms, databases and tools • 3 Evolution of plant morphology o 3.1 Overview of plant evolution o 3.2 Evolution of meristems 3.2.1 Diversity in meristem architectures 3.2.2 Role of the KNOX-family genes 3.2.3 Evolution of the meristem architecture o 3.3 Evolution of leaves 3.3.1 Origins of the leaf 3.3.2 Factors influencing leaf architectures 3.3.3 Genetic evidences for leaf evolution o 3.4 Evolution of flowers 3.4.1 Origins of the flower 3.4.2 Evolution of the MADS-box family 3.4.3 Factors influencing floral diversity 3.4.4 Flowering time 3.4.5 Theories of flower evolution o 3.5 Evolution of secondary metabolism • 4 Mechanisms and players in evolution • 5 See also • 6 Suggested readings • 7 ReferencesHistorical perspective Before 1900 Johann Wolfgang von Goethe The origin of the term "morphology" is generally attributed to Johann Wolfgang von Goethe. He was of the opinion that there is an underlying fundamental organisation (Bauplan) in the diversity of flowering plants. In his book titled The Metamorphosis of Plants, he proposed that thePlant anatomy, From Wikipedia, the free encyclopedia 27
  28. 28. Bauplan enabled us to predict the forms of plants that had not yet been discovered.[3]Goethe also was the first to make the perceptive suggestion that flowers consist ofmodified leaves.In the middle centuries, several basic foundations of our current understanding of plantmorphology were laid down. Nehemiah Grew, Marcello Malpighi, Robert Hooke,Antonie van Leeuwenhoek, Wilhelm von Nageli were just some of the people whohelped build knowledge on plant morphology at various levels of organisation. It was thetaxonomical classification of Carolus Linnaeus in the eighteenth century though, thatgenerated a firm base for the knowledge to stand on and expand.[4] The introduction ofthe concept of Darwinism in contemporary scientific discourse also had had an effect onthe thinking on plant forms and their evolution.Wilhelm Hofmeister, one of the most brilliant botanists of his times, was the one todiverge away from the idealist way of pursuing botany. Over the course of his life, hebrought an interdisciplinary outlook into botanical thinking. He came up with biophysicalexplanations on phenomena like phototaxis and geotaxis, and also discovered thealternation of generations in the plant life cycle.[5]1900 to the presentArabidopsis thaliana. This flowering plant has been a model system for most of plantmolecular studiesThe past century witnessed a rapid progress in the study of plant anatomy. The focusshifted from the population level to more reductionist levels. While the first half of thecentury saw expansion in developmental knowledge at the tissue and the organ level, inthe latter half, especially since the 1990s, there has also been a strong impetus on gainingmolecular information.Edward Charles Jeffrey was one of the early evo devo researchers of the 20th century. Heperformed a comparative analyses of the vasculatures of living and fossil Gymnospermsand came to the conclusion that the storage parenchyma has been derived fromtracheids.[6] His research[7] focussed primarily on plant anatomy in the context ofphylogeny. This tradition of evolutionary analyses of plant architectures was furtheradvanced by Katherine Esau, best known for her book The Plant Anatomy. Her workfocussed on the origin and development of various tissues in different plants. Workingwith Cheadle, she also explained the evolutionary specialization of the phloem tissuewith respect to its function.Plant anatomy, From Wikipedia, the free encyclopedia 28
  29. 29. In the meantime, by the beginning of the latter half of 1900s, Arabidopsis thaliana hadbegun to be used in some developmental studies. The first collection of Arabidopsisthaliana mutants were made around 1945.[8] However it formally became established as amodel organism only in 1998.[9]Wikispecies has information related to:ArabidopsisThe recent spurt in information on various plant-related processes has largely been aresult of the revolution in molecular biology. Powerful techniques like mutagenesis andcomplementation were made possible in Arabidopsis via generation of T-DNAcontaining mutant lines, recombinant plasmids, techniques like Transposon Tagging etc.Availability of complete physical and genetic maps,[10] RNAi vectors, rapidtransformation protocols are some of the technologies that have significantly altered thescope of the field.[11] Recently, there has also been a massive increase in the genome andEST sequences[12] of various non-model species, which, coupled with the Bioinformaticstools existing today, generate interesting opportunities in the field of plant evo devoresearch.Organisms, databases and toolsThe sampling of the Floral Genome ProjectThe most important model systems in plant development have been Arabidopsis andMaize. Maize has traditionally been the favorite of plant geneticists, while extensiveresources in almost every area of plant physiology and development are available forArabidopsis. Apart from these, Rice, Antirrhinum, Brassica, Tomato are also being usedin a variety of studies. The genomes of Arabidopsis and Rice have been completelyPlant anatomy, From Wikipedia, the free encyclopedia 29
  30. 30. sequenced, while the others are in process.[13]. It must be emphasized here that theinformation from these "model" organisms form the basis of our developmentalknowledge. While Brassica has been used primarily because of its convenient location inthe phylogenetic tree in the mustard family, Antirrhinum is a convenient system forstudying leaf architecture. Rice has been traditionally used for studying responses tohormones like abscissic acid and gibberelin as well as responses to stress. However,recently, not just the domesticated rice strain, but also the wild strains have been studiedfor their underlying genetic architectures.[14]Some people have objected against extending the results of model organisms to the plantworld. One argument is that the effect of gene knockouts in lab conditions wouldnt trulyreflect even the same plants response in the natural world. Also, these supposedly crucialgenes might not be responsible for the evolutionary origin of that character. For thesereasons, a comparative study of plant traits has been proposed as the way to go now.[15]Since the past few years, researchers have indeed begun looking at non-model, "non-conventional" organisms using modern genetic tools. One example of this is the FloralGenome Project, which envisages to study the evolution of the current patterns in thegenetic architecture of the flower through comparative genetic analyses.[16] Like the FGP,there are several such ongoing projects that aim to find out conserved and diversepatterns in evolution of the plant shape. Expressed sequence tag (EST) sequences of quitea few non-model plants like Sugarcane, Apple, Lotus, Barley, Cycas, Coffee, to name afew, are available freely online. The Cycad Genomics Project,[17] for example, aims tounderstand the differences in structure and function of genes between gymnosperms andangiosperms through sampling in the order Cycadales. In the process, it intends to makeavailable information for the study of evolution of structures like seeds, cones andevolution of life cycle patterns. Presently the most important sequenced genomes from anevo-devo point of view include those of A.thaliana (a flowering plant), Poplar (a woodyplant), Physcomitrella patens (a bryophyte), Maize (extensive genetic information), andChlamydomonas reinhardtii (a green alga). The impact of such a vast amount ofinformation on understanding common underlying developmental mechanisms can easilybe realised.Apart from EST and genome sequences, several other tools like PCR, Yeast two hybridsystem, microarrays, RNA Interference, SAGE, QTL mapping etc. permit the rapid studyof plant developmental patterns. Recently, cross-species hybridization has begun to beemployed on microarray chips, to study the conservation and divergence in mRNAexpression patterns between closely related species.[18] Techniques for analyzing this kindof data have also progressed over the past decade. We now have better models formolecular evolution, more refined analysis algorithms and better computing power as aresult of advances in computer sciences.Evolution of plant morphologyOverview of plant evolution Main article: Evolutionary history of plantsEvidence suggests that an algal scum formed on the land 1,200 million years ago, but itwas not until the Ordovician period, around 500 million years ago, that land plantsappeared. These begun to diversify in the late Silurian period, around 420 million yearsago, and the fruits of their diversification are displayed in remarkable detail in an earlyDevonian fossil assemblage known as the Rhynie chert. This chert preserved early plantsPlant anatomy, From Wikipedia, the free encyclopedia 30
  31. 31. in cellular detail, petrified in volcanic springs. By the middle of the Devonian periodmost of the features recognised in plants today are present, including roots, leaves andseeds. By the late Devonian, plants had reached a degree of sophistication that allowedthem to form forests of tall trees. Evolutionary innovation continued after the Devonianperiod. Most plant groups were relatively unscathed by the Permo-Triassic extinctionevent, although the structures of communities changed. This may have set the scene forthe evolution of flowering plants in the Triassic (~200 million years ago), whichexploded the Cretaceous and Tertiary. The latest major group of plants to evolve were thegrasses, which became important in the mid Tertiary, from around 40 million years ago.The grasses, as well as many other groups, evolved new mechanisms of metabolism tosurvive the low CO2 and warm, dry conditions of the tropics over the last 10million years.Evolution of meristemsThe meristematic cells give rise to various organs of the plant, and keep the plantgrowing. The Shoot Apical Meristem (SAM) gives rise to organs like the leaves andflowers. The cells of the apical meristems - SAM and RAM (Root Apical Meristem)-divide rapidly and are considered to be indeterminate, in that they do not possess anydefined end fate. In that sense, the meristematic cells are frequently compared to the stemcells in animals, that have an analogous behavior and function.Diversity in meristem architecturesIs the mechanism of being indeterminate conserved in the SAMs of the plant world? TheSAM contains a population of stem cells that also produce the lateral meristems while thestem elongates. It turns out that the mechanism of regulation of the stem cell numbermight indeed be evolutionarily conserved. The CLAVATA gene CLV2 responsible formaintaining the stem cell population in Arabidopsis is very closely related to the Maizegene FASCIATED EAR 2(FEA2) also involved in the same function.[19] Similarly, inRice, the FON1-FON2 system seems to bear a close relationship with the CLV signalingsystem in Arabidopsis.[20] These studies suggest that the regulation of stem cell number,identity and differentiation might be an evolutionarily conserved mechanism inmonocots, if not in angiosperms. Rice also contains another genetic system distinct fromFON1-FON2, that is involved in regulating stem cell number.[21] This example underlinesthe innovation that goes about in the living world all the time.Role of the KNOX-family genesNote the long spur of the above flower. Spurs attract pollinators and confer pollinatorspecificity. (Flower:Linaria dalmatica)Plant anatomy, From Wikipedia, the free encyclopedia 31
  32. 32. Complex leaves of C.hirsuta are a result of KNOX gene expressionGenetics screens have identified genes belonging to the KNOX family in this function.These genes essentially maintain the stem cells in an undifferentiated state. The KNOXfamily has undergone quite a bit of evolutionary diversification, while keeping the overallmechanism more or less similar. Members of the KNOX family have been found inplants as diverse as Arabidopsis, rice, barley and tomato. KNOX-like genes are alsopresent in some algae, mosses, ferns and gymnosperms. Misexpression of these genesleads to formation of interesting morphological features. For example, among membersof Antirrhinae, only the species of genus Antirrhinum lack a structure called spur in thefloral region. A spur is considered an evolutionary innovation because it definespollinator specificity and attraction. Researchers carried out transposon mutagenesis inAntirrhinum, and saw that some insertions led to formation of spurs that were verysimilar to the other members of Antirrhinae[22], indicating that the loss of spur in wildAntirrhinum populations could probably be an evolutionary innovation.The KNOX family has also been implicated in leaf shape evolution (See below for amore detailed discussion). One study looked at the pattern of KNOX gene expression inA.thaliana, that has simple leaves and Cardamine hirsuta, a plant having complex leaves.In A.thaliana, the KNOX genes are completely turned off in leaves, but in C.hirsuta, theexpression continued, generating complex leaves.[23] Also, it has been proposed that themechanism of KNOX gene action is conserved across all vascular plants, because there isa tight correlation between KNOX expression and a complex leaf morphology.[24]Evolution of the meristem architectureThe meristem architectures do differ between angiosperms, gymnosperms andpteridophytes. The gymnosperm vegetative meristem lacks organization into distincttunica and corpus layers. They possess large cells called Central Mother Cells in themeristem. In angiosperms, the outermost layer of cells divides anticlinally to generate thenew cells, while in gymnosperms, the plane of division in the meristem differs fordifferent cells. However, the apical cells do contain organelles like large vacuoles andstarch grains, like the angiosperm meristematic cells.Plant anatomy, From Wikipedia, the free encyclopedia 32
  33. 33. Pteridophytes, like fern, on the other hand, do not possess a multicellular apicalmeristem. They possess a tetrahedral apical cell, which goes on to form the plant body.Any somatic mutation in this cell can lead to hereditary transmission of that mutation.[25]The earliest meristem-like organization is seen in an algal organism from group Charalesthat has a single dividing cell at the tip, much like the pteridophytes, yet more simpler.One can thus see a clear pattern in evolution of the meristematic tissue, frompteridophytes to angiosperms. Pteridophytes, with a single meristematic cell;gymnosperms with a multicellular, but less defined organization and finally,angiosperms, with the highest degree of organization. The genetic innovations thatcontributed to this evolution are yet not clearly known.Evolution of leaves For a discussion on Evolution of Photosynthesis, see Photosynthesis.Origins of the leaf Further information: Evolutionary history of plants#leaves and MegaphyllLeaf lamina. The leaf architecture probably arose multiple times in the plant lineageLeaves are the primary photosynthetic organs of a plant. Based on their structure, they areclassified into two types - microphylls, that lack complex venation patterns andmegaphylls, that are large and with a complex venation. It has been proposed that thesestructures arose independently.[26] Megaphylls, according to the Telome hypothesis, haveevolved from plants that showed a three dimensional branching architecture, throughthree transformations - planation, which involved formation of a planar architecture,webbing, or formation of the outgrowths between the planar branches and fusion, wherethese webbed outgrowths fused to form a proper leaf lamina. Studies have revealed thatthese three steps happened multiple times in the evolution of todays leaves.[27]It has been proposed that the before the evolution of leaves, plants had the photosyntheticapparatus on the stems. Todays megaphyll leaves probably became commonplace some360mya, about 40my after the simple leafless plants had colonized the land in the earlyDevonian period. This spread has been linked to the fall in the atmospheric carbondioxide concentrations in the Late Paleozoic era associated with a rise in density ofstomata on leaf surface. This must have allowed for better transpiration rates and gasexchange. Large leaves with less stomata would have gotten heated up in the suns heat,but an increased stomatal density allowed for a better-cooled leaf, thus making its spreadfeasible[28][29].Plant anatomy, From Wikipedia, the free encyclopedia 33
  34. 34. Factors influencing leaf architecturesSpiny leaves of Aciphylla squarrosa. It is thought that these leaves evolved as anadaptation against the now extinct MoasVarious physical and physiological forces like light intensity, humidity, temperature,wind speeds etc. are thought to have influenced evolution of leaf shape and size. It isobserved that high trees rarely have large leaves, owing to the obstruction they generatefor winds. This obstruction can eventually lead to the tearing of leaves, if they are large.Similarly, trees that grow in temperate or taiga regions have pointed leaves, presumablyto prevent nucleation of ice onto the leaf surface and reduce water loss due totranspiration. Herbivory, not only by large mammals, but also small insects has beenimplicated as a driving force in leaf evolution, an example being plants of the genusAciphylla, that are commonly found in New Zealand. The now extinct Moas fed uponthese plants, and its seen that the leaves have spines on their bodies, which probablyfunctioned to discourage the moas from feeding on them. Other members of Aciphyllathat did not co-exist with the moas, do not have these spines.[30]Genetic evidences for leaf evolution At the genetic level, developmental studies have shown that repression of the KNOX genes is required for initiation of the leaf primordium. This is brought about by ARP genes, which encode transcription factors. Genes of this type have been found in many plants studied till now, and the mechanism i.e. repression of KNOX genes in leaf primordia, seems to be quite conserved. Interestingly, expression of KNOX genes in leaves produces complex leaves. It is speculated that the ARP function arose quite early in vascular plant evolution, because members of the primitive group Lycophytes also have a functionally similar gene. Other players that have a conserved role in defining leaf primordia are the phytohormone auxin, gibberelin and cytokinin. The diversity of leavesPlant anatomy, From Wikipedia, the free encyclopedia 34
  35. 35. One interesting feature of a plant is its phyllotaxy. The arrangement of leaves on the plantbody is such that the plant can maximally harvest light under the given constraints, andhence, one might expect the trait to be genetically robust. However, it may not be so. Inmaize, a mutation in only one gene called abphyl (ABNORMAL PHYLLOTAXY) wasenough to change the phyllotaxy of the leaves. It implies that sometimes, mutationaltweaking of a single locus on the genome is enough to generate diversity. The abphylgene was later on shown to encode a cytokinin response regulator protein.[31]Once the leaf primordial cells are established from the SAM cells, the new axes for leafgrowth are defined, one important (and more studied) among them being the abaxial-adaxial (lower-upper surface) axes. The genes involved in defining this, and the otheraxes seem to be more or less conserved among higher plants. Proteins of the HD-ZIPIIIfamily have been implicated in defining the adaxial identity. These proteins deviate somecells in the leaf primordium from the default abaxial state, and make them adaxial. It isbelieved that in early plants with leaves, the leaves just had one type of surface - theabaxial one. This is the underside of todays leaves. The definition of the adaxial identityoccurred some 200 million years after the abaxial identity was established[32]. One canthus imagine the early leaves as an intermediate stage in evolution of todays leaves,having just arisen from spiny stem-like outgrowths of their leafless ancestors, coveredwith stomata all over, and not optimized as much for light harvesting.How the infinite variety of plant leaves is generated is a subject of intense research. Somecommon themes have emerged. One of the most significant is the involvement of KNOXgenes in generating compound leaves, as in tomato (see above). But this again is notuniversal. For example, pea uses a different mechanism for doing the same thing[33][34].Mutations in genes affecting leaf curvature can also change leaf form, by changing theleaf from flat, to a crinky shape,[35] like the shape of cabbage leaves. There also existdifferent morphogen gradients in a developing leaf which define the leafs axis. Changesin these morphogen gradients may also affect the leaf form. Another very important classof regulators of leaf development are the microRNAs, whose role in this process has justbegun to be documented. The coming years should see a rapid development incomparative studies on leaf development, with many EST sequences involved in theprocess coming online.Evolution of flowersFor a more ecological discussion on the evolution of flowers, go to Flower orEvolutionary history of plantsThe pollen bearing organs of the early flower CrossothecaA flower is, arguably, one of the most beautiful products of evolution. Flower-likestructures first appear in the fossil records some ~130 mya, in the Cretaceous era[36].Plant anatomy, From Wikipedia, the free encyclopedia 35
  36. 36. The flowering plants have long been assumed to have evolved from within thegymnosperms; according to the traditional morphological view, they are closely allied tothe gnetales. However, recent molecular evidence is at odds to this hypothesis,[37][38] andfurther suggests that gnetales are more closely related to some gymnosperm groups thanangiosperms,[39] and that gymnosperms form a distinct clade to the angiosperms,[39][37][38].Molecular clock analysis predicts the divergence of flowering plants (anthophytes) andgymnosperms to ~300 mya[40]Phylogeny of anthophytes and gymnosperms, from [41] Cycads Angiosperms Ginkgo Cycads Bennettitale Conifers s Anthophytes Bennettitales Ginkgo Gnetales Conifers Angiosperm Gnetale s s Traditional view Modern viewThe main function of a flower is reproduction, which, before the evolution of the flowerand angiosperms, was the job of microsporophylls and megasporophylls. A flower can beconsidered a powerful evolutionary innovation, because its presence allowed the plantworld to access new means and mechanisms for reproduction.Origins of the flowerAmborella trichopoda : Amborellaceae is considered the sister family of all floweringplants (magnified image)The family Amborellaceae is regarded as the sister family of all living flowering plants.That means members of this family were most likely the first flowering plants.It seems that on the level of the organ, the leaf may be the ancestor of the flower, or atleast some floral organs. When we mutate some crucial genes involved in flowerdevelopment, we end up with a cluster of leaf-like structures. Thus, sometime in history,the developmental program leading to formation of a leaf must have been altered togenerate a flower. There probably also exists an overall robust framework within whichPlant anatomy, From Wikipedia, the free encyclopedia 36
  37. 37. the floral diversity has been generated. A example of that is a gene called LEAFY (LFY),which is involved in flower development in Arabidopsis. The homologs of this gene arefound in angiosperms as diverse as tomato, snapdragon, pea, maize and evengymnosperms. Interestingly, expression of Arabidopsis LFY in distant plants like poplarand citrus also results in flower-production in these plants. The LFY gene regulates theexpression of some gene belonging to the MADS-box family. These genes, in turn, act asdirect controllers of flower development.Evolution of the MADS-box familyThe members of the MADS-box family of transcription factors play a very important andevolutionarily conserved role in flower development. According to the ABC Model offlower development, three zones - A,B and C - are generated within the developingflower primordium, by the action of some transcription factors, that are members of theMADS-box family. Among these, the functions of the B and C domain genes have beenevolutionarily more conserved than the A domain gene. Many of these genes have arisenthrough gene duplications of ancestral members of this family. Quite a few of them showredundant functions.The evolution of the MADS-box family has been extensively studied. These genes arepresent even in pteridophytes, but the spread and diversity is many times higher inangiosperms[42]. There appears to be quite a bit of pattern into how this family hasevolved. Consider the evolution of the C-region gene AGAMOUS (AG). It is expressed intodays flowers in the stamens, and the carpel, which are reproductive organs. Itsancestor in gymnosperms also has the same expression pattern. Here, it is expressed inthe strobili, an organ that produces pollens or ovules[43]. Similarly, the B-genes (AP3 andPI) ancestors are expressed only in the male organs in gymnosperms. Their descendantsin the modern angiosperms also are expressed only in the stamens, the male reproductiveorgan. Thus, the same, then-existing components were used by the plants in a novelmanner to generate the first flower. This is a recurring pattern in evolution.Factors influencing floral diversityWikiversity has bloom time data for Linaria vulgaris on the Bloom ClockThe various shapes and colors of flowersHow is the enormous diversity in the shape, color and sizes of flowers established? Thereis enormous variation in the developmental program in different plants. For example,monocots possess structures like lodicules and palea, that were believed to be analogousto the dicot petals and carpels respectively.It turns out that this is true, and the variation isdue to slight changes in the MADS-box genes and their expression pattern in themonocots. Another example is that of a plant called Linaria vulgaris, which has twoPlant anatomy, From Wikipedia, the free encyclopedia 37
  38. 38. kinds of flower symmetries-radial and bilateral. These symmetries are due to epigeneticchanges in just one gene called CYCLOIDEA.[44]Large number of petals in roses has probably been a result of human selectionArabidopsis has a gene called AGAMOUS that plays an important role in defining howmany petals and sepals and other organs are generated. Mutations in this gene give rise tothe floral meristem obtaining an indeterminate fate, and many floral organs keep ongetting produced. We have flowers like roses, carnations and morning glory, for example,that have very dense floral organs. These flowers have been selected by horticulturistssince long for increased number of petals. Researchers have found that the morphology ofthese flowers is because of strong mutations in the AGAMOUS homolog in these plants,which leads to them making a large number of petals and sepals.[45] Several studies ondiverse plants like petunia, tomato, Impatiens, maize etc have suggested that theenormous diversity of flowers is a result of small changes in genes controlling theirdevelopment[46].Some of these changes also cause changes in expression patterns of the developmentalgenes, resulting in different phenotypes. The Floral Genome Project looked at the ESTdata from various tissues of many flowering plants. The researchers confirmed that theABC Model of flower development is not conserved across all angiosperms. Sometimesexpression domains change, as in the case of many monocots, and also in some basalangiosperms like Amborella. Different models of flower development like the The fadingboundaries model, or the Overlapping-boundaries model which propose non-rigiddomains of expression, may explain these architectures.[47] There is a possibility that fromthe basal to the modern angiosperms, the domains of floral architecture have gotten moreand more fixed through evolution.Flowering timeAnother floral feature that has been a subject of natural selection is flowering time. Someplants flower early in their life cycle, others require a period of vernalization beforeflowering. This decision is based on factors like temperature, light intensity, presence ofpollinators and other environmental signals. We know that genes like CONSTANS (CO),FLC and FRIGIDA regulate integration of environmental signals into the pathway forflower development. Variations in these loci have been associated with flowering timevariations between plants. For example, Arabidopsis thaliana ecotypes that grow in thecold, temperate regions require prolonged vernalization before they flower, while thetropical varieties, and the most common lab strains, dont. We now know that thisvariation is due to mutations in the FLC and FRIGIDA genes, rendering them non-functional.[48]Quite a few players in this process are conserved across all the plants studied. Sometimesthough, despite genetic conservation, the mechanism of action turns out to be different.Plant anatomy, From Wikipedia, the free encyclopedia 38
  39. 39. For example, rice is a short-day plant, while Arabidopsis is a long-day plant. Now, inboth plants, the proteins CO and FLOWERING LOCUS T (FT) are present. But inArabidopsis, CO enhances FT production, while in rice, the CO homolog represses FTproduction, resulting in completely opposite downstream effects[49].Theories of flower evolution Main article: Evolutionary history of plants#flowersThere are many theories that propose how flowers evolved. Some of them are describedbelow.The Anthophyte Theory was based upon the observation that a gymnospermic groupGnetales has a flower-like ovule. It has partially developed vessels as found in theangiosperms, and the megasporangium is covered by three envelopes, like the ovarystructure of angiosperm flowers. However, many other lines of evidence show thatGnetales is not related to angiosperms.[41] Further information: anthophytaThe Mostly Male Theory has a more genetic basis. Proponents of this theory point outthat the gymnosperms have two very similar copies of the gene LFY while angiospermsjust one. Molecular clock analysis has shown that the other LFY paralog was lost inangiosperms around the same time as flower fossils become abundant, suggesting thatthis event might have led to floral evolution.[50] According to this theory, loss of one ofthe LFY paralog led to flowers that were more male, with the ovules being expressedectopically. These ovules initially performed the function of attracting pollinators, butsometime later, may have been integrated into the core flower.One theory also suggests that humans have been one of the reasons for the diversity offlowers. This theory suggests that since the early settlers found flowers beautiful, theymay have started selecting for them artificially.[51] The flowers may have evolved toexploit the ecological niche being opened because of humans finding them attractive. Thevalidity of this theory, however, is debatable, not least because flowers starteddiversifying long before they came into contact with humans.Evolution of secondary metabolismStructure of Azadirachtin, a terpenoid produced by the Neem plant, which helps ward offmicrobes and insects. Many secondary metabolites have complex structuresAlthough we know a lot of secondary metabolites produced by plants, the extent of thesame is still unfathomable. Secondary metabolites are essentially low molecular weightPlant anatomy, From Wikipedia, the free encyclopedia 39
  40. 40. compounds, sometimes having complex structures. They function in processes as diverseas immunity, anti-herbivory, pollinator attraction, communication between plants,maintaining symbiotic associations with soil flora, enhancing the rate of fertilization etc,and hence are significant from the evo-devo perspective. The structural and functionaldiversity of these secondary metabolites across the plant kingdom is so huge that it isestimated that hundreds of thousands of enzymes might be involved in this process in theentire of the plant kingdom, with about 15-25% of the coding genome coding for theseenzymes. Despite this, every species has its unique arsenal of secondary metabolites.[52]Many of these metabolites are of enormous medical significance to humans.What is the purpose of having so many secondary metabolites being produced, with asignificant chunk of the metabolome devoted to this activity? It is hypothesized that mostof these chemicals help in generating immunity, and in consequence, the diversity ofthese metabolites is a result of a constant war between plants and their parasites. There isevidence that this may be true in many cases. The big question here is the reproductivecost involved in maintaining such an impressive inventory. Various models have beensuggested that probe into this aspect of the question, but a consensus on the extent of thecost is lacking.[53] We still cannot predict whether a plant with more secondarymetabolites would be better-off than other plants in its vicinity.Secondary metabolite production seems to have arose quite early during evolution. Evenbacteria possess the ability to make these compounds. But they assume more significantroles in life from fungi onwards to plants. In plants they seem to have spread out usingdifferent mechanisms like gene duplications, evolution of novel genes etc. Furthermore,studies have shown that diversity in some of these compounds may be positively selectedfor.Although the role of novel gene evolution in the evolution of secondary metabolismcannot be denied, there are several examples where new metabolites have been formed bysmall changes in the reaction. For example, cyanogen glycosides have been proposed tohave evolved multiple times in different plant lineages. There are several such instancesof convergent evolution. For example, we now know that enzymes for synthesis oflimonene - a terpene - are more similar between angiosperms and gymnosperms than totheir own terpene synthesis enzymes. This suggests independent evolution of thelimonene biosynthetic pathway in these two lineages.[54]Mechanisms and players in evolutionThe stem-loop secondary structure of a pre-microRNA from Brassica oleraceaWhile environmental factors are significantly responsible for evolutionary change, theyact merely as agents for natural selection. Change is inherently brought about viaphenomena at the genetic level - mutations, chromosomal rearrangements and epigeneticchanges. While the general types of mutations hold true across the living world, in plants,some other mechanisms have been implicated as highly significant.Plant anatomy, From Wikipedia, the free encyclopedia 40