Instructions for printer-friendly copy.

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(click on pic for source)

    Land Plant Diversity

    Plants are our life and breath.

    There are 435,000 described species of land plants.

    About 40% are considered very rare, and endangered by climate change and other anthropogenic factors.

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    Embryophyte Diversity

    Embryophytes can be broadly classified as

      I. Non-vascular (Bryophytes)
        A. Liverworts
        B. Hornworts
        C. Mosses

      II. Vascular (Tracheophytes)
        A. Seedless
          1. Lycophytes (Club "Mosses")
          2. Pterophytes (Ferns and their relatives)
        B. Seed-bearing
          1. Gymnosperms (naked seed plants)
          2. Anthophytes (angiosperms/flowering plants)

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    Life Cycle Stage Swap

    In bryophytes
    • The gametophyte is the
      dominant, persistent life cycle stage.

    • The sporophyte is ephemeral,
      lasting only one reproductive season.

    In tracheophytes
    • The sporophyte is the
      dominant, persistent life cycle stage.

    • The gametophyte is ephemeral,
      lasting only one reproductive season.

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    Asexual Reproduction

    Plants can reproduce asexually via cloning:
    • growing from broken-off parts

    • growing new individuals from runners

    • producing asexual plantlets

    Aspen trees form the largest organisms on earth (by mass)
    A clone colony can be 8 km (5 mi) long.

    The largest such colony is Pando,
    in the Fishlake National Forest in Utah.

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    Sexual Reproduction

    Depending on species, a plant
    (either gametophyte or sporophyte) can be

    dioecious

      and reproductive structures are on separate individuals

    monoecious

      and reproductive structures are on a single individual, but on different branches.

    bisexual/
    hermaphroditic

      and components are on a single individual and are combined in a single branch/structure.

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    Multicellular Sex Organs

    A multicellular organ that produces gametes
    is known as a gametangium.
    (Greek: gamete, "gamete" and angion, "box")

    Gametangia are present only in the gametophyte,
    and may be either female or male.

    • A female archegonium produces an ovum.

    • A male antheridium produces sperm.

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    The Bryophytes

    There are three extant phyla of non-vascular plants.

    • Hepatophyta - liverworts

    • Anthocerophyta - hornworts

    • Bryophyta - mosses

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(click on pic for source)

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(click on pic for source)

    Bryophyte Characters

    Bryophytes

    • lack xylem and phloem (no organs)

    • have a very thin waxy cuticle

    • have stomates fixed in open position

    • release flagellated sperm into the environment
      (so require at least a thin film of water for reproduction)

    • are sometimes considered the
      "amphibians of the plant kingdom"

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(click on pic for source)

    Ancestral Threads

    A moss gametophyte begins life as a
    branching, threadlike protonema.
    (Greek proto, "first" and nema, "thread")

    The protonema bears a strong resemblance
    to filamentous green algae, a close relative.

    More complex organisms are the result of more complex ontogenies.

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(Leiomitra lanata; click on pic for source)

    Hepatophyta: The Liverworts

    Liverworts have a flattened thallus anchored
    to the substrate via threadlike rhizoids.

    The rhizoids are not true roots,
    as they lack vascular tissue.


    (click on pic for source)

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    Liver and Wort

    Liverworts' common name is derived from

    • the mammalian organ it supposedly resembles

    • wort, the Anglo-Saxon word for "herb"

    Because of its resemblance to the liver,
    ancient peoples (e.g., Romans) believed that
    liverwort could be used as a tonic liver ailments.

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    The Doctrine of Signatures

    The Doctrine of Signatures (dating from ~ 50AD)
    states that plants resembling a particular body part can be used to treat ailments of that body part.

    Botanist William Coles (1626-1662) wrote that this resemblance was a "message from God",
    telling man how to use these plants.

    Some people still believe the Doctrine of Signatures.


    But would you trust someone
    who can't spell potato, tomato, or scrotum?

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    Gemmae: Asexual Babies in Cups

    The gametophytes reproduce asexually by budding
    tiny plantlets called gemmae in gemmae cups.

    When it rains, gemmae are splashed out of the cups
    and washed away to grow in a new spot.

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(click on pic for source)

    Stalked Sex

    About 80% of liverwort species are dioecious.
    The other 20% are monoecious

    Male and female are easily distinguishable
    when producing gametes.

    • Males grow antheridiophores.
      • These bear antheridia on the upper surface.

    • Females grow archegoniophores.
      • These bear archegonia on the lower surface.

      Sperm swim from the antheridia to the archegonia
      when there is sufficient moisture in the environment.

      You know the rest.

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(click on pic for source)

    Liverworts: The Sporophyte

    Like all embryophytes, liverworts grow their sporophytes
    ' within the archegonium.

    After they release their yellow spores,
    the sporophytes and archegoniophore will wither.

    But the thallus will remain and do it again next year.

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(click on pic for source)

    Anthocerophyta: The Hornworts

    Hornworts are named for the elongated, horn-like sporophyte
    that sprouts seasonally from the gametophyte.

    Hornworts have a worldwide distribution, though they will grow only
    in localities with sufficient humidity.

    They may grow in soil or as epiphytes .

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(click on pic for source)


(click on pic for source)

    Bryophyta: The Mosses

    The mosses are the most derived
    and most diverse bryophytes.

    Some species contain a thin strand
    of conducting tissue
    running through
    the center of the upright thallus.

    These are primordia of true stems and leaves.

    Mosses are important both ecologically and economically.

    • retain soil in rainy habitats
    • produce peat, used as fuel

    Various species of mosses may be either

    • monoecious
    • dioecious

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    The Tracheophytes

    Most of the plants you see around you
    are the sporophytes of vascular plants.

    The gametophyte is tiny and ephemeral.

    Tracheophyte synapomorphies make them well-suited
    for a fully terrestrial existence.

    • xylem and phloem

    • highly lignified
      • structural support
      • allows high turgor pressure in xylem

    • thick waxy cuticle

    • stomates open and close with turgor pressure

    • highly differentiated tissues and organs

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(click on pic for source)

    Tracheophytes:
    Seedless and Seed-bearing

    All plants produce spores.
    Only some plants enclose the spore in a seed.

    Tracheophytes can be broadly categorized as

    • Seedless
      • Lycophytes (Club "mosses")
      • Pterophytes (Ferns, horsetails, whisk ferns)

    • Seed-bearing
      • Gymnosperms (naked-seed plants)
      • Angiosperms (flowering plants)

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Lycopodium spp.

    Seedless Tracheophytes:
    Lycopodiophyta,
    The Club Mosses

    The most primitive seedless vascular plants are the club "mosses",

    They are not mosses.
    They are vascular plants.
    (They only look sort of mossy.)

    There are only two extant genera:
    Lycopodium and Selaginella


Selaginella spp.

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(click on pic for source)

    The Strobilus

    Club mosses were the first plants
    to produce sporophylls,
    leaves specialized to bear sporangia.

    Sporophylls grow in whorled clusters,
    forming a strobilus, or cone.

    Club moss species may be

    • dioecious (heterosporous)
      • microspores --> male gametophytes
      • megaspores --> female gametophytes

    • monoecious (homosporous)
    • spores --> bisexual gametophytes

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    Seedless Tracheophytes:
    Pteriodiophyta:
    Ferns, Horsetails,
    and Whisk Ferns

    This large group comprises more than 11,000 species, and are second only to the flowering plants in diversity.

    The most familiar are the ferns.

    <--- The Adder's Tongue Fern, Ophioglossum reticulatum, has more chromosomes--1260--than any other living organism. And yet how tiny!

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(photo by Kimi Palmer, Star Tribune, UK)

    Fiddleheads

    Young leaves in most species emerge
    as coiled structures known as fiddleheads,
    (for obvious reasons).

    Although some fiddleheads are edible,
    others contain toxins! Know your species.


    (photo by Katy Enka, Getty Images)

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(photo by Rror, Wikimedia Commons)

    Horsetails

    Horsetails are close cousins of the "true" ferns.

    • Horsetails are also called "scouring rushes"
      because they were used by early Americans
      to scrub cooking vessels.

    • The hollow stems are impregnated with silica
      that deters herbivores, but also
      makes them good for scrubbing.

    • The stems also are used to shape the reeds of
      instruments such as clarinets, bassoons, and oboes.

    In spring, they form strobili of whorled sporophylls.


(photo by Anne Elliott, Flickr)

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(click on pic for source)

    Whisk Ferns

    Whisk Ferns (Psilotum spp.) were once thought to be
    the most primitive tracheophytes because of their
    strong resemblance to the earliest fossil tracheophytes.
    • no roots
    • no leaves
    • simple sporangia borne on stems

    Molecular analysis revealed that they are actually derived, atavistic ferns.

    Leaflike scales lack vascular tissue,
    and are called enations.

    You can see them growing as epiphytes around
    Coral Gables and other areas in southern Florida.

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