The phylogeny of land plants The likely ancestor are charophycean algae Chloroplast DNA and...
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The phylogeny of land plantsThe likely ancestor are charophycean algae
Chloroplast DNA and ribosomal RNA indicate charophycean algae and land plants had common ancestorMembranes 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
Chara
Land plant life cycle
Gametophyte (1N)
Eggs or sperm
Sporophyte (2N)
Spores (1N)
Major evolutionary events in land plant evolution
1) Invasion of land
Bryophyta
Lack true roots, stems and leavesInstead have rhizoids, caulalia and phyllodes
Require moisture for fertilization
Without vascular tissue; rely on diffusion
Dispersal by spores
Gametophyte is dominant stage
Lack cuticle
Bryophyta (moss)
Bryophyta (hornwort)
Bryophyta (liverworts)
Major evolutionary events in land plant evolution
2) The evolution of vascular tissueXylem 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)
Lycophyta - club mosses
Do not produce seeds
Spores borne on strobili
Pterophyta (ferns)
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 seedsA seed is a structure that encloses and protects a developing embryo
6) evolution of pollination
Seed plants
Gametophyte much reduced and dependent on sporophyteSeed consists of sporophyte embryo packaged along with a food supply within a protective coatAdapted for terrestrial existencePollination replaces swimming as the mechanism for delivering sperm to the egg
GymnospermsNaked seedsLack 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 pollinationWater 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
Ginkophyta
Cycadophyta
Stem unbranched with terminal palm-like leaves
Cone-like sporophylls
Cycadophyta (cycads)
Gnetophyta
Flower-like cones
Xylem composed of tracheids and vessel elements
Pits
Figure 28.4a
Tracheids
Perforatedend walls
Figure 28.4b
Vessels
Gnetophyta (Ephedra or Mormon Tea)
Shrub of American deserts
Gnetophyta (Welwitschia)
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
Coniferophyta
Coniferophyta
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 hypothesesMagnolia 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
Amborella
New Caledonia
Amborella
Water lilies
Monocots
Monocots - parallel venation
Dicots
Dicots - reticulate venation
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!!