Overview of plant classification

Overview of plant classification

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  Overview of Plant Classification Dr.Anil V. Dusane Associate Professor, Sir Parashurambhau College, Pune anildusane@gmail.com
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  What is classification? It is an ancient activity of every culture.  It is the grouping of organisms according to their characteristics.  It is the hierarchical organization.  Each level of hierarchy (grouping) is called taxa.  Science of classifying organisms is known as taxonomy. (taxis- arrangement, nomos-rule). Taxonomy is a science of differentiating, grouping and giving names (nomenclature) to living things.
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  Important Steps inTaxonomy  Identification  Description  Nomenclature  Phylogeny(evolution)  Classification
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  Analogy with Libraryclassification system
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  Taxonomic categories King Phillip  Came  Over  For  Good  Soup KingdomPhylum Class Order Family Genus Species Military Organization Biological Organization Brigade (two or more regiments) Kingdom (one or more phyla) Regiment (two or more battalions) Phylum/Division (one or more classes) Battalion (two or more companies) Class (one or more orders) Company (two or more platoons) Order (one or more families) Platoon (two or more squads) Family (one or more genera) Squad (a group of 12 soldiers) Genus (one or more species) Soldier (a distinct kind or unit) Species (a distinct kind or unit)
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  Taxon  Mainly thereare seven levels of ranks of classification.  Hierarchal arrangement  Kingdom > Phylum/Division > Class > Order > Family > Genus > Species >Variety  Kingdom  Phylum/Division  Class  Order  Family  Genus  Species (smallest unit)
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  Herbarium  It isa collection of preserved plants that are stored, catalogued, and arranged systematically for study.
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  Taxon … Rank HumanPea Kingdom Animalia Plantae Phylum or Division Chordata Magnoliophyta Class Mammalia Magnoliopsida Order Primates Fabales Family Hominidae Fabaceae Genus Homo Pisum Species H. sapiens P. sativum
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  Importance of classification It is a primary way to organize and store the basic information (typically of species).  It would be impossible to deal with enormous plant diversity (350,000 species of plants) without proper classification.  It helps to keep the track of information for the purpose of conservation management, inventories, commerce, etc.  It provides information about relationships among various groups.
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  Importance of classification All the species in the same genus share common biochemical, ecological and biological properties.  It throws a light on evolutionary relationships, ancestry and relatedness.  Cladograms reflect ancestry and relatedness of individual taxa (evolutionary diagram).  Classification has a predictive value.  Importance in Biodiversity (existence of different forms of a species).
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  Problems in plantclassification  Some changes in scientific name.  Scientific names are frequently misspelled.  Many organisms yet to be classified. Vinca roseus Catharanthus roseus
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  Landmarks of classification Aristotle-Grouped the animals   John Ray- Defined “Species” Linnaeus- Father of taxonomy Concept of Binomial nomenclature
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  Nomenclature  Binomial nomenclaturehas been developed by Linnaeus.  It has Binomial nomenclature i.e. Genus and species.  It is Latinized, unique and universal.  Genus- It is Capitalized, Italicized.  Species- Written in lower case, italicized.  E.g. Binomial nomenclature of Mango is Mangifera indica
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  Concept of species Itis a group of actually or potentially interbreeding natural populations which are reproductively isolated from other groups.
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  Taxonomical aids  Herbarium Botanical gardens  Museums  National Parks  Institutes-Botanical Survey of India (BSI)  Monographs  Diagnostic Keys  Scientific journals
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  Benefits of Herbarium It acts a source of information to determine, what the plants look like, where it is found, what environmental niche it occupy, what morphological and chemical variation occurs and, when it flower or produce seed.  Specimens can be used to provide samples of DNA to study relationships and evolutionary processes.  It acts as vouchers to validate scientific observations.  It is used to identify species.  It is important in discovery of new species.
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  Kew Herbarium https://www.kew.org/science/collections-and-resources/collections/herbarium • TheHerbarium at the Royal Botanic Gardens Kew houses approximately 7 million specimens, collected from all around the world. Specimens are either pressed and dried or preserved. • Kew herbarium collection is one of the largest in the world. • It represents global vascular plant diversity, containing around 95% of vascular plant genera and 330,000 type specimens, which act as standards for identifying the correct name for a plant.
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  Botanical Gardens Botanical gardenis an establishment where plants are grown for scientific study and display to the public.
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  National parks An areaof countryside, or occasionally sea or fresh water, protected by the state for the preservation of wildlife.
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  Monographs  Term "monographia"is derived from the Greek mono ("single") and grapho ("to write"), meaning "writing on a single subject.  It is a comprehensive treatment of a taxon.  Monographs typically review all known species within a group, add any newly discovered species, and collect and synthesize available information on the ecological associations, geographic distributions, and morphological variations within the group.  The first-ever monograph of a plant taxon was Robert Morison’s ‘Plantarum Umbelliferarum Distributio Nova’, a treatment of the Apiaceae.
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  Identification keys  Itis a printed information or a computer software package.  It is dichotomous and not having more than two alternatives.  Language of a key is telegraphic.
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  Example of Keys KEYTO CLASSES OF VASCULAR PLANTS IN NEW SOUTH WALES 1 Plants not reproducing by seeds. 2 Stems prominently jointed: leaves whorled, forming a sheath at stem nodes. CLASS 3 SPHENOPSIDA 2* Stems not jointed; leaves absent or if present, not whorled and forming a sheath at the nodes. 3 Sporangia borne on stems, in the axils of leaves or leaf-like organs, or embedded in the expanded bases of such organs. 4 Sporangia fused to form synangia. CLASS 1 PSILOPSIDA 4* Sporangia not fused into synangia. CLASS 2 LYCOPSIDA 3* Sporangia borne otherwise (on leaves or in nut-like sporocarps). CLASS 4 FILICOPSIDA 1* Plants reproducing by seeds. 5 Ovules not enclosed in a carpel; ovules arranged in cones or solitary on a short fleshy axis (non-flowering seed plants). 6 Leaves pinnate. CLASS 5 CYCADOPSIDA 6* Leaves simple. CLASS 6 CONIFEROPSIDA 5* Ovules enclosed in a carpel; carpels arranged in flowers (flowering plants). CLASS 7 MAGNOLIOPSIDA Curtsey: http://plantnet.rbgsyd.nsw.gov.au/trad_keys.htm
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  Type of Dataused for classification Morphological Pollination Reproductive biology Anatomy Chromosomes Palynology Chemistry Molecular
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  Morphological Data • Morphologicaldata are the features of external form or appearance. • It provides nearly all the characters used for plant identification. • It is useful in phylogenetic studies and other systematic studies. • Morphological data has always and still is the predominant type of data used in plant systematic studies. • It defines the limit of species. • It provides a classification in agreement with evolutionary relationships.
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  Morphological data sources Field samples  Herbarium samples  Qualitative characters  Quantitative characters  Data from vegetative and reproductive parts of the plants. Types of vegetative morphological characters  Duration and habit  Root types/parts  Stem types/parts  Leaf types/parts  Floral morphology
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  Morphological characteristics Characteristics offlower and fruit are used to classify Closely related species of Boerhaavia
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  Anatomical evidences  Anatomyis related to the internal structure. The evidences come from:  (i) Wood cell type, size and shape,  (ii) Wood cell wall sculpture, pattern,  (iii) Stealer pattern,  (iv) Vascular bundle type,  (v) Xylem type, wood type and ray type,  (vi) Ground tissue type,  (vii) Epidermal type,  (viii) Mesophyll type,  (ix) Scleried type,  (x) Stomatal type,  (xi) Trichome type, crystal type,  (xii) Nodal type,  (xiii) Ventation type,  (xiv) Petiole vasculation type,  (xv) Periderm origin,  (xvi) Pholem cell type, and  (xvii) Specialized cell type.
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  Anatomical evidences  Anatomicaldata is used to resolve phylogenetic problems.  Nonporous wood is the characteristic feature of gymnosperms while porous wood is found in angiosperms.  A progressives evolution in angiosperms from small tracheids to long narrow vessels with lignified thickening of various types is evident through anatomical details.  Wood anatomy reveals that Gnetales are not ancestral to angiosperms and Amentiferae and Gnatales constitute a relatively advanced group.  In Gnetales, the vessels arose from tracheids with circular pittings while in angiosperms they evolve from tracheids with scalariform pitting.  Vesselless angiosperms of Winteraeae, Trochodendraceae Tetracentraceae are primitive angiosperms.  Wood anatomy supports the separation of Austrobaileya and Paeonia to separate family as Austrobaileyacae and Paeoniaceae respectively.
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  Anatomical evidences  Thereare several closely related families which are separated on the basis of stomatal type.  Anomocytic stomata are characteristic of Ranunculaceae while Diacytic stomata in Caryophyllaceae and Paracytic in Rubiacace.  Unicellular or multicellular non- glandular trichomes (epidermal appendages) in Moraceae and Brassicaceae.  Stellate hairs are present in Malvaceae, Peltate hairs in Olea, branched dendroid hairs in Styrax and candelabrum types in Verbascum.  Occurrence of Kranz anatomy in leaf suggests presence of C4 cycle of photosynthesis.
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  Evidences from Palynology Palynology is the science that deals with Pollen grains.  Morphology of Pollen grains is used in classification.  Pollen grains may be vesiculate (with air sacs); saccate or non saccate, fenestrate or non-fenestrate, colpate (furrows or colpi present) or porate (apertures present at the poles).
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  Basic characteristics ofpollens  (i) Pollen unit type,  (ii) Pollen grain polarity,  (iii) Pollen grain shape,  (iv) Pollen grain symmetry,  (v) Pollen grains nuclear state,  (vi) Pollen wall architecture,  (vii) Exine stratification,  (viii) Exine structure,  (ix) Exine sculpture,  (x) Aperture type,  (xi) Aperture number,  (xii) Aperture position,  (xiii) Aperture shape, and  (xiv) Aperture structure.
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  Evidences from Palynology In Magnoliidae, pollens are binucleate while Caryophyllidae has trinucleate pollens.  In Asclepiadaceae pollens present in Pollinia.  Linaceae and Plumbagineae shows greater similarity than that of Plumbagineae and Staliceae based on palynology.  Napenthaceae and Droseraceae (except Drosophyllum) have spinuliferous pollen tetrads. Such type of pollen tetrads are not found in any other plant.  Close relationship between Polygalaceae and Ephedraceae has been established based on similarity between their pollen grains.  On the basis of Palynological characters Fumariaceae is separated from Papaveraceae and Nelumbonaceae from Nymphaeaceae.  Malvacae and Bombacaceae are separated on the basis of palynological studies where Malvaceae shows spinose exine and Bombacacee shows reticulate exine in Pollen grains.
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  Evidences from Embryology Embryology is the study of successive stages of sporogenesis, gametogenesis and the development of embryo.  Basic evidences are obtained using following characteristics:  (i) Anther loculi number, arrangement,  (ii) Anther wall formation and endothecium type,  (iii) Archesporial cell number,  (iv) Aril presence,  (v) Embryo sac development type,  (vi) Embryo and Embryogeny type,  (vii) Endosperm type,  (viii) Integument number and structural type,  (ix) Ovule orientation type and position,  (x) Tapetal type,  (xi) Perisperm presence,  (xii) Nucellus character, and  (xiii) Haustorium formation type.
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  Evidences from Embryology Embryological evidences are important at higher category level e.g., in conjunction with other types of evidences in confirming the systematic position of taxa.  In Asteridae the ovules are unitegmic and tenuinucellate, in Caryophyllidae the ovules are bitegmic.  In Cyperaceae only one microspore per microspore mother cell is formed.  In Onagraceae the embryosac is 4 nucleate, oenothera type as compared to normal 8 nucleated Polygonum type.  Exocarpus was separated from Santalaceae to a new family Exocarpaceae however after studying the embryology of the genus Exocarpus is kept under family Santalaceae.  Paeonia which earlier kept in Ranunculaceae is now separated to distinct family Paeoniaceae on the basis of centrifugal stamens and floral anatomy.
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  Cytological evidences  Cytologyis the study of the morphology and physiology of cells.  Cytological evidences is used for distinguishing taxa; to determine the origin of groups and to understand the evolutionary history of related taxa.  In cases of controversy, cytological studies are used for determining the categories of genus and species.  Chromosome homology studies are used in knowing the degree of genetic relationship. Some evidential characteristics are:  (i) Chromosome number, structure, type,  (ii) Chromosome meiotic behaviour,  (iii) Ploidy level and type, and  (iv) Chromosome aberration.
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  Cytological evidences  Onthe basis of chromosome morphology, Pandanus and Typha are kept under two different orders viz. Pandanales and Typhales.  Angiosperm, the chromosome number varies greatly e.g., n = 2 in Haplopappus gracilis (Asteraceae) and highest is n = 132 in Poa litloroa (Poaceae).  In Ranunculaceae, it is generally x = 8. Thallictrum and Aquilegia have x = 7.  In Poaceae the subfamily Poideae has x = 7 and Bambusoideae has x =12.  Ploidy level also plays a significant role in taxonomy e.g., Triticum contains diploid (2n = 14), Triploid (2n = 21) and Hexaploid (2n = 42).
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  Cytological evidences  Basedon different nature of karyotype of Butomus from Limnocharis, Hydrocharis, Tenagocharis, it is kept in Butomaceae while others are retained in Alismataceae.  Karyotype(structure of genome) study of members of Agavaceae confirms the shifting of Agave from Amaryllidaceae (inferior ovary) and Yucca from Liliaceae (superior ovary) into Agavaceae.  Cyperaceae and Juncaceae were separated due to the distinct floral structure however, based on the holocentric chromosomes these are considered closely related.  Meiotic behaviour of chromosomes is helpful in comparing the genomes to detect degree of homology e.g., Triticum aestivum is haxaploid (A A B B D D)where ‘A’ is derived from T. monococcum (diploid) and ‘B’ from Aegilops speltoides and D is derived from Aegilops squarrosa (diploid).
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  Evidences from Chemo-taxonomy Thescience of chemical taxonomy is based on classification of Plants on the basis of their chemical constituents related with the molecular characteristics. Following basic chemical characteristics are used  (i) Flavonoids,  (ii) Terpenoids,  (iii) Carotenoids,  (iv) Polysaccharides,  (v) Alkaloids,  (vi) Amino acids,  (vii) Fatty acids,  (viii) Aromatic compounds, and  (ix) C3-C4 photosynthesis
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  Evidences from Chemo-taxonomy Morphologically similar plants possess similar chemicals.  Micro molecules, macromolecules, primary metabolites and secondary metabolites has important role in the classification of plants.  Mentzar (1966) provided biogenetic classification on the basis of natural relationships between various chemical constituents.  Lathyrus martinus has a specific protein which is absent in other species of Lathyrus.  The members of Asteraceae lack unsaturated lipids while the members of Acanthaceae, Annonaceae and Malvaceae are oleic and palmitic rich.  In Pinus every species has different type of terpentine.  In Lichens, chemical methods are largely used for the identification of genera an species.  Chemistry of Betacyanins led to recognition of 10 families containing them (Centrospermae). They do not occur in plants containing anthocyanins.
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  Evidences from Chemo-taxonomy Asteraceae is divided in two tribes Tubiflorae and Liguliflorae on the presence of latex (chemical substances).  Four species of Nyssa and eleven species of Cornus and one species each of Dauidua, Camptotheca etc. are analysed and observed the percentage of Palmitic, Stearic, Linolic acid etc. and found that Nyssa biflora lies intermediate to N. sylvatica and N. aquatica.  Terpenoid and glycosides are present in Apocynaceae and Moraceae.  Sesquiterpene Lactones is a group of bitter tasting compounds. Out of 1400 in Asteraceae 1340 are present.  Cronquist has shown evolution of Asteraceae on this basis i.e., Rubiales → Dipsacales → Asteraceae, rather than through Campanulales where Lactones are altogether absent.  The absence of ellagic acid in monocots and its presence in Nymphaeales does not support the views of Cronquist and Takhtajan who were of the opinion that Nymphaeales have given rise to monocots.
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  Numerical taxonomy (taximetrics) It is a classification system in biological systematics which deals with the grouping by numerical methods of taxonomic units based on their character states.  The concept was first developed by Robert R. Sokal and Peter H. A. Sneath in 1963.  It aims to create a taxonomy using numeric algorithms like cluster analysis rather than using subjective evaluation of their properties.  It has two major components i.e. Phenetics and cladistics. In Phenetics, classifications is based on the patterns of overall similarities and in cladistics, the classifications are based on the branching patterns of the estimated evolutionary history of the taxa.
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  Cladogram A cladogram (fromGreek clados "branch" and gramma "character") is a diagram used in cladistics to show relations among organisms.
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  Thank you Dr. A.V.Dusane anildusane@gmail.com