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The phylogeny of land plants. The likely ancestor are charophycean algae Chloroplast DNA and ribosomal RNA indicate charophycean algae and land plants had common ancestor Membranes of land plants and charophyceans have rosette-shaped arrays of proteins that make the cell walls
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The phylogeny of land plants • The likely ancestor are charophycean algae • Chloroplast DNA and ribosomal RNA indicate charophycean algae and land plants had common ancestor • Membranes of land plants and charophyceans have rosette-shaped arrays of proteins that make the cell walls • Other algae have linear arrays • Land plants and charophyceans have anti-photorespiration enzymes packaged into organelles called peroxisomes • Peroxisomes not found in other algae • Similarity of sperm of land plants and charophycean algae
Land plant life cycle Gametophyte (1N) Spores (1N) Eggs or sperm Sporophyte (2N)
Major evolutionary events in land plant evolution • 1) Invasion of land
Bryophyta • Lack true roots, stems and leaves • Instead have rhizoids, caulalia and phyllodes • Require moisture for fertilization • Without vascular tissue; rely on diffusion • Dispersal by spores • Gametophyte is dominant stage • Lack cuticle
Major evolutionary events in land plant evolution • 2) The evolution of vascular tissue • Xylem for conduction of water • Phloem for conduction of carbohydrates from leaves or fronds to other parts of plant body • 3) Sporophyte is dominant phase of life cycle • 4) Cutin lines external surfaces
Vascular plants • Roots, stems and leaves present • Presence of vascular tissue
Lycophyta - club mosses • Do not produce seeds • Spores borne on strobili
Pteridophyta - ferns • Do not produce seeds • Spores produced in sori on the underside of fertile fronds
Major evolutionary events in land plant evolution • 5) evolution of seeds • A seed is a structure that encloses and protects a developing embryo • 6) evolution of pollination
Seed plants • Gametophyte much reduced and dependent on sporophyte • Seed consists of sporophyte embryo packaged along with a food supply within a protective coat • Adapted for terrestrial existence • Pollination replaces swimming as the mechanism for delivering sperm to the egg
Gymnosperms • Naked seeds • Lack the enclosed chambers (ovaries) in which angiosperm ovules and seeds develop • Rather, gymnosperm ovules and seeds develop on the surfaces of specialized leaves called sporophylls • Wind pollination • Water not needed for pollination • All are woody plants (no herbaceous species) • Date from 350 mybp
Ginkgophyta • Only one species • Tree with fan-shaped leaves • Ovules develop into yellow, cherry-like seeds
Cycadophyta • Stem unbranched with terminal palm-like leaves • Cone-like sporophylls
Gnetophyta • Flower-like cones • Xylem composed of tracheids and vessel elements
Figure 28.4a Tracheids Pits
Figure 28.4b Vessels Perforated end walls
Gnetophyta (Ephedra or Mormon Tea) • Shrub of American deserts
Welwitschia • Found in the Nabib Desert • Two enormous leaves,the longest lived of any plant • Grow about five inches a year • Each leaf can reach several hundred square feet in size
Coniferophyta • Sporophylls modified into cones • Wind-pollinated • Xylem with tracheids but no vessels
Major evolutionary events in land plant evolution • 7) Evolution of flowers and fruits
Anthophyta - flowering plants • Reproductive organs within a flower • Gametophytes greatly reduced • Ovules embedded within sporophyte tissue (ovary) • Seeds within a fruit • Appeared in early Cretaceous • Most pollination by insects and birds
The origin of the angiosperms • Darwin wrote about “the abominable mystery” of what the first flowering plant looked like • Angiosperms appear suddenly in the fossil record with no obvious ancestors for a period of 80-90 million years before their appearance • Two hypotheses • Magnolia hypothesis • First angiosperm was a tree with complex flowers • Paleoherb hypothesis • First angionsperm was a non-woody plant with simple flowers
Amborella • Analysis of DNA reveals this genus is the most primitive flowering plant • Flowers with moderate number of petals • Flowers are imperfect (separate male and female gametophytes) • Found only on island of New Caledonia in the South Pacific
Diversity of various phyla of land plants • Bryophyta - 18,600 species • Lycophyta - 1,000 species • Pterophyta - 12,000 species • Ginkophyta - 1 species • Cycadophyta - 100 species • Gnetophyta - 70 species • Coniferophyta - 550 species • Anthophyta - 250,000 species!!
