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The chlorophytes and charophytes are not the only green algal clades
- Green Algae-
- Characteristics
- · Chlorophylls a and b
- · Starch storage
- · Cellulose in cell walls
- The closest relatives to land plants
- Key common characteristics with land plants:
- · Egg retention in the parental organism
- · Plasmodesmata join the cytoplasm of adjacent cells
- · Growth is apical (from the tip) and branching
- · Similar peroxisome content, mechanics of cell division, and chloroplast structure
- Charophytes live at the margin of marshes and ponds and probably gave rise to the early land plants 400 to 500 million years ago
- Adaptations to Land
- Water is difficult to obtain and retain on land
- Adaptations to land:
- · Cuticle: hydrophobic, waxy covering that retards water loss
- · Protected reproductive structures
- Land plant life cycle—alternation of generation
- Gametophyte: haploid stage which produces gametes by mitosis
- Sporophyte: diploid stage which produces spores by meiosis
- Spores: unicellular dispersal units with thick walls that resist dessication and decay (haploid)
- Adaptations to life on land distinguish land plants from green algae
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Land plants have been divided into 10 major clades
A major division of the clades is based on whether or not the plants have tracheids—special fluid conducting cells
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They are photosynthetic
- Thought to be similar to the earliest land plants
- Liverwort : 9,000 species (Marchantia sp.)
- Moss: 15,000 species (Polytrichum sp.)
- Hornwort: 100 species (Anthoceros sp.)
- Short plants – water moves by diffusion
- Most are terrestrial, growing in dense mats in moist habitats
- Gametophyte is the dominant generation
- The sporophyte is dependent on the gametophyte
- Gametophyte:
- · Dominant
- · “nutritionally” independent
- · Produces haploid gametes by mitosis
- Fertilization: requires water for sperm movement to eggs
- Sporophyte:
- · Protected by the gametophyte
- - Remains attached
- - Not “nutritionally” independent
- · Produces haploid spores by meiosis
- Spores:
- · Dispersal unit
- · Germinate to form a protonema
- · Protonema grow into a gametophyte
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- What are the differences among clades?
- Liverworts don’t have stomata
- Used for gas exchange (and saving water)
- Another adaptation to life on land!
- Mosses don’t have a persistently green sporophyte
- Hornworts do- similar to higher land plants
- Applications?
- Nonvasculars are more interesting than economically important
- Exception: Sphagnum sp. Moss
- · Dense mats get compressed into peat
- · Used for fuel
- · Also very absorbent; used for gardening, field dressing of wounds, and diapers
- Peat bogs are interesting ecosystems
- · Acidic
- · Low oxygen
- · Slow decomposition
- · Cover approximately 1% of Earth’s land surface (about half the size of the U.S.)
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Seed-less Vascular Plants
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Produce vascular tissues, but not seeds
- Vascular tissues (xylem and phloem) facilitate transport
- Lignified xylem cells (tracheids) provide rigid structural support
- Allow for vertical growth!
- So what?
- · Compete for sunlight
- · Disperse spores
- Another major adaptation of life!
- Club Mosses – Lycopodium sp. (1,200 species)
- Horsetails – Equisetum sp (15 species)
- Whisk Ferns- Psilotum sp. ( 15 species)
- Ferns – Dryopterus sp. (12,000 species)
- More vertical and branching growth form
- More photosynthetic area and spores than un-branched forms
- Sporophyte is the dominant generation
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- The sporophyte and gametophyte are both independent
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- Notes for 9-23-10
- Sporophyte:
- · Dominant
- · Potentially long-lived
- · Produces sporangia which produce spores by meiosis
- · Spores may disperse great distances before germination to form a gametophyte
- Gametophyte:
- · Much less noticeable
- · Short-lived
- · Produces haploid gametes by mitosis
- Fertilization:
- Requires water for sperm movement to eggs
- Notice that the embryo is still protected as it develops into a sporophyte
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- What are the differences among the seed-less vasculars?
- Club mosses have microphylls (simple scale-likes leaves)
- Horsetails have reduced megaphylls that form whorls
- Whisk ferns have reduced or no megaphylls
- Ferns have large megaphylls with branching vascular strands
- Leptosporangiate: lepton = “thin”, referring to sporangia with walls only one cell thick
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