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.

    Of these, 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 Swapping

    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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    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)

    Bryophyte Characters

    Bryophytes
    • lack xylem and phloem
      x(thus, lack true organs)
    • have a very thin waxy cuticle
    • have stomates fixed in open position
    • release flagellated sperm directly into the environment
      x(thus 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 was a tonic for the liver.

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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.
      • Antheridiophores bear antheridia on their upper surface.

    • Females grow archegoniophores.
      • Archegoniophores bear archegonia on their 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 erect portion of the thallus,
    forming the 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, but 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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Selaginella spp.

    Seedless Tracheophytes:
    Lycopodiophyta,
    The Club Mosses

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

    They are not mosses, of course.
    They are vascular plants.
    Their moss-like appearance was the problem.

    There are only two extant genera:
    Lycopodium and Selaginella


Lycopodium spp.

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(click on pic for source)

    The Strobilus

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

    Sporophylls grow in whorled clusters in the spring,
    forming a structure called 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, Whisk Ferns

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

    The most familiar pteridophytes 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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Spermatopsida - The Seed Plants

The seed plants are the dominant eukaryotic life forms on the planet.
There are five extant phyla.

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    Cycadophyta

    The Cycadophyta (cycads, or sago "palms") appear in the fossil record
    in the early Permian (~280 mya).

    Their diversity plummeted after the K-T extinction.

    Cycads are characterized by

    • short, stout trunk
    • slow-growing vascular cambium
    • whorl of tough, pinnately compound leaves
    • dioecy (distinct male and female strobili)
    • long-lived; some known to be 1000 years old

    Superficially resemble ferns and palms, but are not closely related to either.
    There are about ~ 300 extant cycad species.

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(click on pic for source)

    Cycad Toxicity

    All genera of cycads contain two powerful neurotoxins
    • β-methylamino-L-alanine (BMAA),
      possibly produced by symbiotic N-fixing cyanobacteria
    • cycasin

    In some human populations that rely heavily on cycads as a source of flour, an unusually high incidence of ALS-like and other neurodegenerative diseases has been reported, although a definitive link to cycad toxins has yet to be established.

    As some humans have learned, though, there are
    labor-intensive methods that can be used to process
    cycad tissue and extract the edible starch.

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    Ginkgophyta

    Ginkgo biloba, the "maidenhair tree" is the only extant species in this phylum.
    It is known from fossils as old as 270 million years.

    The genus name is believed to be derived from
    the Japanese gin kyo, "silver apricot"

    Native to China, Ginkgo is widely cultivated as a source of

    • food
    • phytochemicals used in traditional medicine

    However, it is nearly extinct in the wild.

    Ginkgos are often planted as ornamentals in cities
    with high levels of traffic, as they are unusually resistant
    to the adverse effects of smog
    .

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(source: Wikimedia Commons)

    Stinky Gingky

    Male trees produce elongate strobili.
    Female trees produce fleshy seeds.

    Although the seed resembles an apricot
    (if you squint), the fleshy part is a seed coat,
    not a fruit.

    The seed coat is permeated with butyric acid,
    which makes it incredibly stinky when ripe or decaying.

    For this reason, male trees are more commonly used as ornamentals.

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(By H. Zell, Wikimedia Commons)

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    Coniferophyta

    Conifers are perhaps the most familiar gymnosperms, including

      • pine
      • spruce
      • fir
      • redwoods
      • cedar
      • cypress
      • juniper
      • larch

      Plants that lose their leaves seasonally are deciduous.

      Most conifers are evergreen, shedding leaves continuously,
      but re-growing them immediately.

      Thus, they can photosynthesize through the short winter days.

      This gives them an adaptive advantage over deciduous trees,
      at least in northern latitudes.

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(click on pic for source)

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(click on pic for source)

    Conifer Leaves are "Needles"

    Conifer leaves are specialized to withstand cold, dry conditions.

    Pine "needles" are specialized leaves with stomates
    recessed in longitudinal grooves to prevent desiccation.

    The cuticle is very thick.
    Thick, internal resins provide herbivore deterrence
    as well as antifreeze properties.

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(source: MacMillan Higher Ed)

    The Conifer Life Cycle

    The conifer life cycle is like that of other gymnosperms.
    • Microsporophylls (2n) grow microsporangia (2n).
    • Microsporangia meiotically produce microspores (n).
    • Each microspore develops into a male gametophyte (n) (pollen (n)) lacking antheridia.
    • Each pollen produces two two sperm (n) .

    • Megasporophylls (2n) grow megasporangia (2n).
    • Megasporangia meiotically produce megaspores (n).
    • One megaspore develops into a female gametophyte (n) (inside the ovule) with two archegonia (n).
    • Each archegonium produces one ovum (n) .

      Boy (n) meets girl (n). Zygote (2n).

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    Conifer Sex

    Most conifers are monoecious.
    • Male gametophytes (pollen) are produced in male strobili.
    • Female gametophytes (in ovules) are produced in female strobili.

    The two cone sexes sometimes grow on separate branches,
    but are found on the same plant.

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    Pine Life Cycle: The Male

    Whorls of microsporophylls form male (staminate) strobili.
    Male strobili are elongate, "papery", and fragile.

    Each microsporophyll bears a microsporangium.
    Inside the microsporangium, meiosis produces microspores.

    Each microspore develops into a male gametophyte that
    • lacks antheridia
    • produces two sperm via mitosis
    • is a pollen grain

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(click on pic for source)

    The Male Gametophyte is Pollen

    Male strobili last only one season, producing copious pollen
    that is distributed by wind.

    Remember:
    Each tiny, yellow grain of pollen is a mature male gametophyte
    containing two sperm.

    Successful pollen will land between the bracts of a female cone
    and grow a tube to deliver sperm to the waiting ovum.

    Pine pollen is sold commercially as a male aphrodisiac.
    (Doctrine of Signatures, anyone?)

    Wind pollinated plants produce huge amounts of pollen.
    <-- Watch the spectacular pine pollen release in the video!

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    Pine Life Cycle: The Female

    <--- In the spring, whorls of megasporophylls form female (pistilate) strobili (cones).

  • Female strobili are fleshy and firm.
    Each megasporophyll bears two megasporangia. --->

  • Inside the megasporangium (2n),
    meiosis produces a megaspore (n).
    It remains enclosed in layers of sporophyte tissue:
    • megasporangium (2n nucellus)
    • outer integuments (2n seed coat)

The sporophyte tissue and megaspore together
comprise the ovule.

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    The Female Gametophyte
    Waits Inside the Ovule

    Surrounded by nutritive nucellus (megasporangium tissue), the megaspore matures into the female gametophyte

    The gametophyte + sporophyte tissue coat still comprise an ovule.

    Each of the female gametophyte's two archegonia produces an ovum.
    Only one of these ova will become the new sporophyte.

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(click on pic for source)

    A Long Wait

    Successful pollen will land between the bracts of a female cone
    and grow a pollen tube to deliver sperm to the waiting ovum.

    Once the ovum and sperm fuse, the ovule is considered a seed.

    In a typical conifer, fertilization occurs a year after pollination.

    Female strobili continue to develop for two years after pollination,
    only then releasing mature seeds.

    (The pine cones gracing your holiday wreath took two years to develop!)

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    Gnetophyta

    Gnetophytes may be the closest gymnosperm relatives of flowering plants, though this is still uncertain.

    There are only three extant genera:

    • Gnetum
    • Welwitschia
    • Ephedra

    Like Anthophytes, Gnetophytes have xylem vessel elements.

    Other vascular plants have only tracheids for water conduction.

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    Anthophyta

    The most diverse and successful phylum of seed plants produces seeds in a whorl of modified leaves comprising a flower.

    Angiosperms/Anthophytes are the most diverse and successful plants, numbering anywhere from 300,000-450,000 species.
    What synapomorphies set angiosperms apart from other plant phyla?

    • flowers
    • fruit
    • double fertilization

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    Remember Monocots and Dicots?

    Anthophytes are sometimes categorized as dicots or monocots,
    based on the number of embryonic leaves (cotyledons) in the seed.

    This distinction is artificial, as only Monocotyledonae is monophyletic.
    Monocotyledonae includes such familiar plants as

    • grasses
    • palms
    • orchids
    • lilies
    • gingers

    All other flowering plants are dicots.

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    Distinguish monocots from eudicots this way:

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