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					Biology 204. LAB 7:    ORIGINS & CLASSIFICATION OF BRYOPHYTES
OBJECTIVES: Be able to identify gross and microscopic specimens as mosses and liverworts. Be able
to identify reproductive structures and explain how all parts connect to the processes and phases of the
life cycles. Also be able to compare and contrast the characteristics of mosses and liverworts with those
of their ancestors and with those of the vascular plants.

BACKGROUND INFORMATION
1. MAJOR CHARACTERISTICS OF LAND PLANTS: all land plants, including bryophytes, have
multicellular tissues, alternation of generation life cycles, cellulose cell walls, and store starch for energy.
Except for a very few parasitic angiosperms, all are photosynthetic (autotrophic). They all evolved on land,
but a few ferns and angiosperms have secondarily returned to aquatic or marine habitats. Vascular plants
(Lab 8) have true xylem and phloem and other characteristics biologists consider more advanced. The
bryophytes are smaller and lacking true roots and stems and leaves, but they are more ancient.

2. CLASSIFICATION AND ORIGIN OF BRYOPHYTES.


                                                         The smooth specimens running from the upper right
                                                         of the picture toward the key are liverworts. They
                                                         are wet from dew in this picture. They don't feel
                                                         slimy because this species has a waxy cuticle on its
                                                         epidermis

                                                         The fuzzier specimens in the middle of the picture
                                                         are mosses.

                                                         The brown needles are mostly from pines (conifers,
                                                         gymnosperms to be studied next week), and the leaf
                                                         in the lower right is from an angiosperm.

 The traditional category of bryophyte (Greek for moss-plants) includes relatively primitive, nonvascular land
   plants. Most textbooks or ID manuals use an older classification with one Bryophyta phylum and three
   classes:
        Musci for mosses
        Hepaticae for liverworts
        Anthocerae for hornworts [hornworts look like liverworts except for having horn-shaped
            reproductive structures (in season, only)].

 Most modern systems of classification have three separate divisions or phyla with
          Bryophyta including only mosses http://www.hcs.ohio-state.edu/hcs300/liver2.htm
                  but two separate phyla for
          the liverworts (Hepatophyta            http://www.hcs.ohio-state.edu/hcs300/liver1.htm and
          hornworts (Anthocerotophyta: http://www.ucmp.berkeley.edu/plants/anthocerotophyta.html ).
The three-phylum system reflects the conclusion that these taxa diverged from a common ancestor very long
ago, like nearly half a billion years ago. Bryophytes, especially liverworts, represent a link between the
primitive algae and the advanced vascular plants which now dominate the globe.
   a. The ancestors of bryophytes were probably the Chara-like green algae which were also the ancestors
   of all higher plants. Older books say that land plants evolved from seaweeds, but contemporary opinion
   is that freshwater algae were the ancestors. Land plants theoretically evolved in two directions from the
   original invading populations of advanced green algae:
         [1] The bryophytes are nonvascular and have gametophytic dominance [this means that most of
         their life cycle is spent in the haploid phase].
         [2] The more successful vascular plants [not bryophytes] all have sporophytic dominance.
         Vascular tissue allows plants to grow larger because of the support it provides as well as its
         efficient transport. Tall plants are better in dealing with predators, competitors, and [in some cases]
         pollinators and seed dispersers. Biologists think that sporophytic dominance is advantageous
         because the recessive genes in diploid cells increase genetic variability, which makes a species
         more likely to survive in the long run. Perhaps bryophytes are relatively unimportant and
         unsuccessful because of their haploid [gametophytic] dominance. Their other limitations include
         having no true roots and no true vascular tissue.


   b. The conquest of land was a critical step in the evolution of higher plants [and later in the evolution
   of land animals who had to wait for plants to conquer land before they could have any food on land].
   Land plants developed solutions to the following problems:
        [1] HOW TO KEEP FROM DRYING OUT--
             All land plants HAVE several tissue layers; this reduced the surface/volume ratio, exposing
                only a few cells to air.
             All land plants, except a few bryophytes, have cuticles [waxy coats] and stomata [closeable
                pores] to control water loss.
             All land plants have multicellular sporangia and/or gametangia, providing extra protection
                for the family jewels.
             All land plants retain the zygote and developing embryo within the female parent for
                protection.
        [2] HOW TO GET FERTILIZER AND WATER NOW THAT THE ENTIRE BODY IS NOT
        SOAKING IN A FERTILIZER BATH--
             The first land plants most likely had symbiotic fungi and bacteria which helped them
                absorb and convert fertilizer materials from the soil and air.
             More advanced land plants, but not bryophytes, have roots to absorb water and fertilizer
                and vascular tissue to transport materials to and from the roots. Bryophytes must absorb
                water and fertilizer through the thallus [=undifferentiated plant body] and thus must live in
                damp habitats.
        [3] HOW TO GET SPERM TO OVA WHEN THERE IS NO WATER FOR THEM TO SWIM
        IN--
             Most land plants have flagellated sperm which must swim; thus they have to wait for a very
                  wet season for reproduction. Only the relatively recent seed plants [not bryophytes] have
                  solved this problem by inventing pollen. Bryophyte and fern sex happens only in damp
                  places.

3. Life Cycle. See lecture material or diagrams in folder 7

4. Importance of Bryophytes. Long-dead bryophytes are major components of peat and fossil fuels (coal,
petroleum, natural gas). After the evolution of vascular plants, most bryophytes became extinct because
they could not compete with taller plants for sun. Today, the surviving bryophytes specialize, like lichens,
in niches where vascular plants can’t survive—bare boulders and branches, muddy creek banks and bogs,
and on soils destroyed by fires and volcanoes and bulldozers. The bryophytes and lichens eventually
improve the habitat so much that higher plants colonize and shade out the bryophytes and lichens except if
the habitat is already too shady for higher plants and the bryophytes manage to hang in there. Other than
their role as pioneers in secondary succession, bryophytes are not major players in food chains except in
some bogs. Even there, nothing seems to eat them, and their corpses accumulate as peat, which has
economic value as fuel in remote areas and as a soil additive for affluent gardeners. Native Americans used
dead sphagnum moss as diapers and bandages, and there’s some evidence that sphagnum contains anti-
bacterial compounds. “Wort” is an old Anglo-Saxon word for “plant,” and the names suggest that Europeans
could have used liverworts for liver medicine. Florist suppliers harvest mosses for terrariums and flower
arrangements and maybe for evolutionary biologists who want to analyze their DNA. And, of course,
campers and hikers and bryologists like to rest on mosses, but not on hornworts or liverworts usually.
Hikers who find and recognize liverworts and hornworts become popular with their comrades because of
their interesting chatter about gameophytic dominance, the doctrine of signatures, and the like. Bryologists
and bryological societies, by the way, study not only bryophytes but often lichens, too.

5. Identification. Bryophyte species are easy to identify with amateur or professional manuals, available in
most libraries.


                                                                                 MALE
                                                                                 GAMETOPHYTES

                                                                                 A male moss gametophyte
                                                                                 has
                                                                                 [a] fuzzy vegetative tissue
                                                                                 [b] sperm inside the male
                                                                                 gametangia (antheridia).
                                                                                 [c] the vegetative tissue
                                                                                 below the antheridia rises
                                                                                 above the rest of the fuzzy
                                                                                 thallus (not shown) on a
                                                                                 [d] stalk-like structure.
                                                                                 [e] shows a primitive
                                                                                 layer, almost an epidermis,
                                                                                 which may have a waxy
                                                                                 cuticle in many species
                                                                                      A hornwort's male
                                                                                      gametophyte is similar
                                                                                      except for its shape, which
                                                                                      is almost like an umbrella
                                                                                      and not fuzzy.
                                                                                      [a] labels the sperm, and
                                                                                      [b] is the wall of the
                                                                                      antheridium. Notice that
                                                                                      it's at least one cell layer
                                                                                      thick.

                                                                                      All the cells in all male
                                                                                      gametophytes are always
                                                                                      haploid.




LABORATORY ACTIVITIES.

1. Learn a typical moss life cycle from the hand-out or from another source which uses the same terms. All
other bryophytes have this life cycle with a few modifications in sporophyte shape and gametangium
location. A few species have unisexual gametophytes. Be sure you understand all terms and processes on
the life cycle diagram.

2. Examine each specimen provided by the management and make sure you can identify it as a moss or
liverwort or hornwort (only if the horn is present). If only a vegetative thallus is present, call it a liverwort
unless the thallus is fuzzy—then guess moss. Be able to locate and identify functions for visible structures
like spore capsule and stalk, thallus, gemma cup (asexual clone mechanism, found on liverworts and
hornworts sometimes) or gametangium-containing horns or umbrella-like structures (if present). Be sure
you can tell whether a specimen, or part of a specimen, is a sporophyte or gametophyte and haploid or
diploid.

3. Study slides of gametophytes and sporophytes for mosses and liverworts. Locate and identify functions
and ploidy for spore capsule, sporangium, spores, archegonium, ovum or zygote or embryonic sporophyte,
antheridium, sperm. Review the moss life cycle and make sure you know HOW and WHERE each of these
structures fits into the life cycle.
FEMALE GAMETOPHYTES                                                 In a typical moss female gametophyte, the
                                                                    archegonia point upward, protected somewhat
A mature female haploid gametophyte in a liverwort has              by vegetative strands which make the moss
[a] a "palm tree" structure with a stalk [c] arising from the       look fuzzy. You should be able to find an
photosynthetic thallus (not shown).                                 ovum or zygote in at least some archegonia.
[b] the ova, and later the zygote, are within the female            Also you may be able to see the canal that the
gametangia (archgonia), which hang down .                           sperm swim through to reach the ovum.


4. Checklist:
    a. Be able to define these terms: cellulose, starch, autotrophic, gametangium, sporangium, antheridium,
    archegonium [like an oogonium only multicellular], oogamy, alternation of generation, gametophytic
    dominance, thallus, spore, meiosis, mitosis, syngamy, spore mother cell, dioecious, monoecious,
    sporophyte, gametophyte, haploid, diploid.

   b. What advantage did each of these contribute in the evolution of plants?
    i. multicellular gametangia
    ii. multicellular tissue layers
    iii. symbiotic fungi
    iv. Charales
                                                    SPOROPHYTES
                                                    The moss sporophyte at left has
                                                    [a] a capsule lid (diploid) which may be covered
                                                    with the remnants of the archgonium (haploid), from
                                                    with it grew.
                                                    [b] are spores (haploid) within a sporangium
                                                    (diploid).
                                                    [c] is other diploid tissue within the sporophyte
                                                    capsule, and
                                                    [d] is the wall of the capsule
                                                    The lower left slide shows the base of the capsule,
                                                    which has a "foot" embedded in the female
                                                    gametophyte (not shown).

                                                    Below (right) is the sporophyte of a liverwort
                                                    growing down from the "palm tree top" [d] of the
                                                    female gametophyte. See if you can label the other
                                                    parts.




More pictures? http://botit.botany.wisc.edu:16080/images/130/Bryophytes/
More Info? http://campus.queens.edu/faculty/jannr/Botany/slimies.htm#Bryophytes

© 2004 jannr@queens.edu

				
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