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One synapomorphy in land plants
development from an embryo protected by tissues from the parent plant; called the embryophytes.
The derived features that the land plants share with green algae (the Chloropohytes and Charophytes) include
Chlorophyll a and b.
Starch as a storage product.
Cellulose in cell walls.
Green plants vs Streptophytes (image)
Green plants vs Streptophytes (Definition)
- Green plants: Streptophytes plus
- ---synapomorphy= chlorophyll b, starch
- •Streptophytes = land plants and closely related green algae (Charophytes),
- ---synapomorphy= all retain egg within the parent body
Coleochaetales (a Charophyte, incl Coleochaete scutata)
shows strong morphological similarities to land plants such as flattened form.
•Charales (group in Charophytes, incl. Chara spp.)
- is mostclosely related to landplants.
- Synapomorphy = branchedapical growth, plasmodesmatajoining cytoplasm of adjacent cells.
Land Plants: Current classification into __ major clades
- Nonvascular plants: Hepatophyta, anthocerophyta, bryophyta
- Vascular plants: 2 non seed, 4 gymnosperms, angiosperms
liverworts, hornworts, and mosses
7 groups which form a clade, all have conducting cells called tracheids
•Nearly 90% of living plant species are Angiosperms (flowering plants).
Plants first appeared on land _________ years ago
7 Characteristics of plant adaptation to life on land
-Cuticle- waxy covering prevents drying.
-Stomata—openings in stems and leaves; regulate gas exchange (except liverworts)
-Gametangia enclosing gametes to prevent desiccation.
-Embryos (young sporophyte) enclosed within protective structure.
-Pigments that protect against UV radiation.
-Thick spore walls (w/ sporopollenin) to prevent drying.
-Mutualistic relationships with a clade of fungi (called glomeromycetes) that allow nutrient uptake from soils.
alternation of generations.
•Includes multicellular diploid (sporophyte) and multicellular haploid (gametophyte) individuals.
•Gametes produced by mitosis unite to form a zygote.
•The transitions between the generations occur at fertilization (to diploid sporophyte) and meiosis (to haploid gametophyte).
female vs male plant
archegonium vs antheridium
__________ is a major theme as plants evolve in complexity
Reduction of the gametophyte generation
For __% of the Earth’s history the land was barren, totally uninhabited by life.
•Land plants probably evolved from______ about _____ during the ___________ of the Paleozoic era.
Charophytes/500 mya/Ordovician period
Primitive vascular plants appear in the fossil record about ____ in the_______.
(in Silurian) were the earliest vascular plants (now extinct) had dichotomous branching, but lacked leaves and roots
They were anchored by rhizomes (horizontal portions of stem) and rhizoids (water-absorbing filaments)
•Lycophytes (club mosses) also appeared in the_____. Monilophytes (ferns and fern allies) appeared in the______.
-These groups had true roots and leaves, and two types of spores.
Clade of monilophytes and seed plants
- Synapomorphy includes overtopping growth
- - new branches grow beyond the others; an advantage in the competition for light.
Two types of leaves:
Microphylls: small, simple leaves, usually one vascular strand. [Club mosses (lycophytes)]
Megaphylls: larger and more complex
Life cycle of the most ancient vascular plants- a single type of spore
•produce one type of gametophyte that has both archegonium and antheridium.
first successful colonizers of land
•Liverworts: 9,000 species.
sporophyte grows from bottom, very short (few mm); no filamentous stage, lie flat.
Some have leafy gametophytes; some have thalloid gametophytes.
A stalk raises the simple sporangium above ground level to allow spores to be dispersed.
Liverworts also reproduce asexually:
By simple fragmentation of the gametophyte;
And by gemmae—lens-shaped clumps of cells in gemmae cups. Gemmae are dispersed by raindrops
•Mosses: 15,000 species.
•Mosses (plus hornworts and vascular plants) have stomata, important in water and gas exchange.
•Mosses are among the most common plants in northern climates (cover ~3% of land surface).
•Some species of bryophytes have water conducting tissues (hydroids, progenitors of tracheids), but they don’t have lignin. Maximum height ~ 50 cm (20 in).
•Moss sporophytes (like vascular plants) grow by apical cell division- a region at the growing tip provides an organized pattern of division, elongation, and differentiation.
•Sphagnum grows in swampy places; upper layers of moss compress lower layers that are beginning to decompose, forming peat; leads to formation of coal.
Hornworts: 100 species.
•Hornworts have simple gametophyte; which are flat plates of cells.
•Two characters distinguish Hornworts from Liverworts AND Mosses:
1. Hornwort cells have a single, large chloroplast.
2. The sporophyte grows from bottom and has no stalk; but has a basal region capable of infinite cell division. Sporophytes can grow up to 20 cm.
•Hornworts have internal cavities filled with nitrogen-fixing cyanobacteria.
The exact evolutionary position of the hornworts is still unclear; sometimes the sister group to the mosses plus the vascular plants (the two groups that express apical cell division)
Seedless Vascular Plants (Nonseed Tracheophytes)
•Must have water for at least one part of the life cycle- for the flagellated, swimming sperm.
-Club mosses (Lycophyta) – primitive leaves (Microphylls).
Pteridophytes (Pteridophyta) – complex leaves (Megaphylls); include ferns (~12,000 living species), horsetails (15 species), whisk ferns (15 species)
the club mosses, spike mosses, and quillworts: 1,200 species.
•Roots and stems have dichotomous branching; leaves are microphylls.
•Some club mosses have sporangia arranged in clusters called strobili.
•Others have sporangia on upper leaf surfaces—sporophylls.
•Lycophytes were dominant during the Carboniferous period.
•One type of coal- cannel coal- is formed almost entirely from the spores of a tree lycophyte Lepidodendron.
- horsetails, whisk ferns, and most ferns, form a clade
- --Horsetails and whisk ferns are monophyletic, ferns are not
•growth is overtopping.
Fifteen species in one genus—Equisetum.
Silica in cell walls—“scouring rushes.”
Have true roots; sporangia are on short stalks called sporangiophore.
Leaves are reduced megaphylls in whorls. Each stem segment grows from the base.
•Whisk ferns: Fifteen species in two genera.
•No roots, but well-developed vascular system.
•Psilotum sp. has scales instead of leaves.
•Whisk ferns were once thought to be descendents of rhyniophytes.
•DNA analysis determined a more modern origin. Evolved from more complex ancestors by reduction or loss of megaphylls and true roots.
12,000 species. Most ferns (97%) belong to this clade.
•Sporangia walls are only one cell thick, borne on a stalk.
•Sporophytes have true roots, stems, and leaves.
•Fern leaf starts development as a coiled “fiddlehead.”
•Independent gametophyte generation restricts habitats available to ferns. Most ferns are in shaded, moist environments because water is required for swimming sperm.
•Tree ferns can reach heights of 20 m.
•DNA research suggests that diversification of modern ferns is fairly recent.
•Ferns may have taken advantage of shady environments created by angiosperm trees.
Fern life cycle
•Spore mother cells in sporangia form haploid spores by meiosis.
•Spores can be blown by wind and develop into gametophyte far from parent plant.
•Fern gametophytes produce antheridia and archegonia, not always at the same time or on the same gametophyte.
•Sperm swim through water to archegonium to fertilize egg.
•Zygote develops into independent sporophyte.
•Sporangia occur on undersides of leaves in clusters called sori.