The evolutionary history of plants begins as the story of adaption to land life.
What we can plants, truly land-adapted multicellular photoautotrophs , are descended from a lineage of one of the “green Algae” and thus are in the clade Archaeplastida.
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(1) Evidence supporting that photo-autotrophs plants, are descended from “green Algae”
Chlorophytes, Charophytes & Plantae share:
* multicellularity * cell walls with cellulose * chloroplasts with same pigment (chlorophyll. a & b). Storage molecule is starch.
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(2) Evidence supporting that photo-autotrophs plants, are descended from “green Algae”
Charophytes also share with Plantae:
* Similar flagellated sperm * Cellulose synthesis proteins (rings) * Cytokinesis process (cell plate formation)
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(3) Evidence supporting that photo-autotrophs plants, are descended from “green Algae”
Sporo-pollenin - a durable polymer that protects:
* zygotes in charophytes * spores in seedless plants * pollen grains in seed plants
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How did selection for land life start?
By 470 mya, multicellular green algae expanded from shallow seas into river & lakes. Green algae along lake shores meant more resources; less competition (=drying), subjected to periodic dehydration, and population with land adaptations thrive.
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Advantages of land:
* \[CO2\] higher * light intensity higher * more minerals * no “herbivores” * no competition
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Disadvantages of Land:
* Risk of desiccation (both adult & gametes) * Divided resources (air vs. land) * No “support” in air
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8 Mechanisms explain how plants derived their characteristics:
“Pioneer” species in poor soils. Moss are major 1° producers in cold or high regions. Sphagnum “peat moss” bogs: important wetlands. Also harvested for fuel & gardening.
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What are Bryophytes?
Lack vascular & supportive tissue. Very thin body: depends on diffusion. With rhizoids for attachment (not true roots).
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Bryophyte Characteristics:
Haploid gametophyte is dominant form:
* Dominant = longest lasting or largest * Make eggs & flagellated sperm * Most are small, low growing moist areas
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Diploid sporophyte depends on --- for food and water.
gametophyte
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Phloem
Move sugar & organic products.
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Xylem
Carries water & materials - most vascular plants have tracheids with walls strengthened by tough polymer: lignin.
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Evolution of Vascular Plants
Unbranched sporophyte → branched sporophyte → supportive vascular tissue → Sporophyte photosynthesis increases (no longer need food from gametophyte)
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Roots evolve from --- ---.
underground stems
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Leaves evolved from --- ---.
branched stems
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Megaphylls
Branched veins
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Sporophylls
Sporangia shift to leaves
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How did the success of seedless vascular plants change the Paleozoic world?
Covered the earth, increasing organic C on land (for food); further increases in O2 levels; reduced CO2 levels; all favoring success of land animals.
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Lycophytes: Relict Group
Closest group to ancestral vascular plants. All now very small. Include club moss & spike moss. Little economic/ecological importance today.
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Lycophytes: Whisk ferns (Psilotum)
Dichotomous branching. No true leaves or roots (lost secondarily).
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Lycophytes: Horsetails (Equisetum)
Jointed hollow stem with tiny leaves. Strobili.
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Lycophytes: Ferns
Most widespread & diverse magnoliophytes. Large megaphylls
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Fern Life Cycle
The life cycle of fern is different from other land plants as both the gametophyte and the sporophyte phases are free living.