1. By: Elaine Wang and Ananya Murali

2. Introduction: Pioneers In a New World
• Transition from water -> land
began in the precambrian
period with cyanobacteria
(green algae)
• Developed into world’s 1st
plants
• Adaptations necessary for
survival on land
- Obtaining and
preserving water
- Reproduction

3. 23.1: Trends In Plant Evolution
• Vascular plants: most diverse plants w/ internal tissue systems that conduct water
and solutes through roots, stems and leaves
• Seedless vascular plants: whisk ferns, lycophytes, horsetails, ferns
• Gymnosperms: seed-bearing vascular plants
– Cycads, ginkgos, gnetophytes, conifers
• Angiosperms: vascular plants w/ flowers and seeds
– Magnoliids, eudicots, monocots
• Bryophytes: nonvascular plants
– Liverworts, hornworts, mosses
• Root systems: underground absorptive structures of a cumulatively large surface
area
– Rapidly take up soil water and mineral ions
– Anchor for plants
• Shoot systems: stems and leaves absorb energy from sun, CO2 from the air
– Developed taller/branched stems after developing the capacity to
synthesize/deposit lignin in cell walls
• Xylem: vascular tissue that distributes water and dissolved ions in plants
• Phloem: vascular tissue that distributes dissolved sugars and other photosynthetic
products

4. 23.1: Trends In Plant Evolution
• Cuticle: protective waxy coat that helps conserve water on hot, dry days
• Stomata (stoma): tiny openings across surfaces of leaves and some stems to
control CO2 absorption and restrict evaporative water loss
• Gametophytes: gamete-producing bodies that dominate the haploid phase of algal
life cycles
– mostly aquatic plants
• Sporophyte: multicelled diploid plant body
• After a diploid zygote undergoes mitosis->Forms spores: haploid resting cells
– fertilization could be timed with suitable environmental conditions
– Diploid dominance is an adaptation to land
• Heterospory: plants that produce 2 types of spores (both seedless an seed-
bearing)
• Homospory: plants that produce one type of spore
• Pollen grains: cellular structures that become mature, sperm-bearing male
gametophytes
– Microspores that reach eggs via air currents, insects, and birds
– Contributed to radiation of seed-bearing plants to high/dry habitats
• Seed: an embryo sporophyte, nutritious tissues, and outer coat; Developed from
female gametophytes

5. 23.2: The Bryophytes
• Species of mosses, liverworts, hornworts
– Adapted to moist habitats
– Mosses, however, can be found in deserts as well
• Sensitive to air pollution
• Most common
• Nonvascular: leaf/stem/root parts lack a xylem or phloem
– Instead, have rhizoids: elongated cells/threadlike absorptive structures that attach the gametophytes
to the soil, and absorb water and minerals
• Show three features that were adaptive during the transition to land
– 1. Cuticle: stomata to prevent water loss
– 2. Cellular jacket around parts that produce sperm/eggs: holds in moisture
– 3. Embryo sporophyte: sporophytes that begin life inside a female gametophyte
• Sporophytes remain attached to the gamete-producing body for nutrition (do not disperse)
• Mosses (most common)
– Gametophytes grow in clusters to form cushiony mounds, or grow in branched patterns on tree
trunks (humid conditions)
– Eggs and sperm develop in gametangia at shoot tips of familiar moss plants
– After fertilization, the zygote develops into a mature sporophyte
• Develop a sporangium: stalk and jacketed structure where spores develop
• o Examples
• Peat mosses: used to soak up water (5x more than cotton), used as antiseptic, and also burned
for electricity
• peat bogs: moist mats of the remains of peat mosses

7. 23.3: Existing Seedless Vascular Plants
• Whisk ferns, lycophytes, horsetails, and ferns
• Different from bryophytes b/c sporophytes that develop independently of gametophytes
– sporophytes that have well-developed vascular tissues
– larger, longer-lived sporophyte phase of its life cycle
• Sporophytes can live on land, while gametophytes cannot
• Lycophytes: small club mosses on the forest floor
– “ground pines”
– sporophytes with true roots, stems, small leaves with vascular tissue
– strobili (strobilius) bear spores that germinate, forming small, free-living gametophytes
• heterosporous
• Whisk ferns: not true ferns; resemble whisk brooms
– have rhizomes: short, branched, mainly horizontal absorptive stems that grow underground
– no leaves, made of scale-like branches
– popular ornamental plants common to tropical/subtropical areas
• Horsetails
– sporophytes have rhizosomes
– scalelike leaves whorl around a hollow, photosynthetic stem
– spores produced inside cone-shaped clusters of leaves at shoot tip
– found in streambank muds and other disrupted habitats
• Ferns
– have rhizosomes and fronds: aerial leaves that coil into what resembles a fiddlehead
– sporangia: clusters of spores on the lower surface of the fronds

8. 23.4: Ancient Carbon Treasures
• Lycophyte trees: giant club mosses that developed during the
Carboniferous era
– strobili that produced 8 billion microspores or hundreds of
megaspores
– 40m tall
• 20m tall horsetails
• Many swamp forests had sediments that compressed undecayed remains
of plants into peat mosses
– Pressure transformed the peat into coal: a renewable fossil fuel

9. 23.5: The Rise Of Seed-Bearing Plants
• Most successful vascular plants because
independent of water for fertilization
– Seed ferns, gymnosperms, angiosperms
• Different than seedless vascular plants because:
– Microspores: develop into pollen grains to carry
sperm to female structures (pollination)
– Megaspores: develop within ovules: female
reproductive structures that, when mature, produce
seed
• § female gametophyte, nutrient rich tissue, jacket of
cell layers (to develop a seed coat)
– Traits to conserve water: Thicker cuticles, stomata
underneath leaves
• Pre-Carboniferous: dominated by seed ferns (simlar
to progymnosperms): earliest seed-producing
plants

10. 23.6: Gymnosperms-Plants With “Naked” Seeds
• Gymnosperm sporophyte stages are conspicuous trees and shrubs; the seeds are rather
unprotected ("naked seeds") perched at the surface of reproductive parts.
• Conifers (Coniferophyta)
– The conifers (cone-bearers) are woody trees with needlelike or scalelike
leaves.
– Most are evergreens, some are deciduous.
– Produce true cones: repro. structures in clusters of papery/wood-like
scales that bear exposed to ovules on upper surface
• Lesser Known Gymnosperms
– Cycads (Cycadophyta)
• These palmlike trees flourished during the Mesozoic era, but only about 100
species still exist--confined to the tropics and subtropics.
• They bear massive cone-shaped strobili that produce either pollen (transferred by
air currents or insects) or ovules.
– Ginkgos (Ginkgophyta)
• From the diversity of this group during the Mesozoic, only one species has survived.
• They are remarkably hardy, showing resistance to insects, disease, and air
pollutants.
– Gnetophytes (Gnetophyta) are the most unusual gymnosperms; they live in tropical and
desert areas.

11. 23.7: A Closer Look At The Conifers
• Pine Life Cycle
– The pine tree produces two kinds of cones:
• Male cones produce sporangia which yield microspores
that develop into pollen grains (male gametophyte).
• Female cones produce ovules that yield megaspores
(female gametophyte).
– Pollination is the arrival of a pollen grain on the
female reproductive parts, after which a pollen tube
grows toward the egg.
– Fertilization, which is delayed for up to a year,
results in a zygote that develops into an embryo
within the conifer seed.
• Deforestation and the Conifers
– Although conifers still dominate in certain climates,
their slow reproductive pace puts them at a
disadvantage compared to angiosperms.
– However, deforestation by clear-cutting for their
commercial value has put them at even greater risk.

13. 23.8: Angiosperms - Flowering,
Seed-Bearing Plants
• Characteristics of Flowering Plants
– Only angiosperms produce specialized reproductive structures called flowers.
• Of all the divisions of plants, angiosperms ("vessel seed") are the most
successful and most diverse.
• Most flowering plants coevolved with pollinators--insects, bats, birds, etc.
– There are three major groups of flowering plants:
• Magnoliids include magnolias, avocados, nutmeg, and black pepper
plants.
• Eudicots include familiar shrubs, trees (except conifers), and herbaceous
plants.
• Monocots include grasses, lilies, and the major food-crop grains.
• Representative Life Cycle--A Monocot
– The diploid sporophyte has extensive root and shoot systems; it also retains
and nourishes the gametophyte.
– Embryos are nourished by the endosperm within the seeds, which are
packaged inside fruits.

14. 23.9: Seed Plants And People
• Artificial selection of plants led to the
development of domesticated grains including
wheat and barley (11,000 yrs ago)
• Different trees have been used for their wood
pliability (paper, furniture, rope)

15. Works Cited
Starr, Cecie and Ralph Taggart. Biology: The
Unity and Diversity of Life. 10th Ed. Belmont:
Brooks/Cole, 2004. Print.