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Bryophytes: Non-Vascular Plants with Sporic Life Cycle - Prof. Robert E. Reeder, Study notes of Biology

An overview of bryophytes, a group of non-vascular plants that undergo a sporic life cycle. Two phyla: hepaticophyta (liverworts) and bryophyta (mosses). It discusses their structure, reproduction, and ecological significance.

Typology: Study notes

Pre 2010

Uploaded on 08/19/2009

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bio1120_bryophytes 3/17/04
BIOL 1120 REEDER
THE BRYOPHYTES
I. Nonvascular plants: Sporic Life Cycle
A. Phylum Hepaticophyta (the liverworts) simpler than the mosses
1. Structure
a. Gametophyte maybe flat, sometimes branched, ribbon-like structures that lie on the
ground, attached to soil by numerous rhizoids on the thallus underside, and lacking a
stem.
1) Flattened, lobed, leaflike body form is called a thallus
2) Lobes of their thalli: superficially resemble human liver lobes
b. Most species grow upright with a leaflike gametophyte; the leafy liverworts have
gametophytes with structures equivalent to stems, branches, and leaves but lack vascular
tissues (not true stems, roots, nor leaves).
c. The leafy liverworts are epiphytic (nonparasitic plants that grow on other plants, using
the host for support) on trees in tropical rain forests.
d. The recognizable plant is the gametophyte generation
e. As in mosses, the sporophyte grows as a parasite on the gametophyte
f. Are largely restricted to damp environments and are inconspicuous
2. Reproduction
a. Sporic type life cycle; true alternation of generations
1) Archegonia and antheridia are produced on the haploid gametophyte
b. Asexual Gemma cups, containing small, ovoid gemmae, can be found on the upper
surface of some liverwort gametophytes; gemmae may separate and grow into new
gametophytes
3. Asexual reproduction can also occur by thallus branching and growth; the individual thallus
lobes elongate and becomes a separate plant when the older thallus dies
B. Phylum Bryophyta (the mosses)
1. Structure
a. Begins as a filamentous green thread, the protonema, that grows from a spore
b. From the protonema grows an erect, green, stemlike organ to which are attached a spiral
whorl of leaf-like structures (haploid gametophyte generation); no true stems nor leaves
(lacks vascular tissue)
c. From the base of the stem extend many colorless, hairlike rootlets called rhizoids (not
true roots)
d. Size of mosses limited to a height of 15 to 20 cm, due to the absence of true vascular and
supporting tissues and the inefficiency of rhizoids as water absorbers
2. Reproduction
a. Sex organs develop at the top of the gametophyte stem in the middle of the leaf whorl.
b. Some species are dioecious (separate sexes), while others are monoecious (individual
containing sex organs of both sexes).
c. Sperm produced in the antheridium (sausage-shaped) are spirally coiled and swim
utilizing two flagella.
d. A rain or heavy dew triggers the sperm release and allows for a medium on the plant by
which the sperm may swim to the female sex organ, the archegonium (flask-shaped
containing one large egg), either on the same plant or on another one (archegonium
releases a chemical to attract the sperm).
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bio1120_bryophytes 3/17/

BIOL 1120 REEDER

THE BRYOPHYTES

I. Nonvascular plants: Sporic Life Cycle A. Phylum Hepaticophyta (the liverworts) simpler than the mosses

  1. Structure a. Gametophyte maybe flat, sometimes branched, ribbon-like structures that lie on the ground, attached to soil by numerous rhizoids on the thallus underside, and lacking a stem. 1) Flattened, lobed, leaflike body form is called a thallus 2) Lobes of their thalli: superficially resemble human liver lobes b. Most species grow upright with a leaflike gametophyte; the leafy liverworts have gametophytes with structures equivalent to stems, branches, and leaves but lack vascular tissues (not true stems, roots, nor leaves). c. The leafy liverworts are epiphytic (nonparasitic plants that grow on other plants, using the host for support) on trees in tropical rain forests. d. The recognizable plant is the gametophyte generation e. As in mosses, the sporophyte grows as a parasite on the gametophyte f. Are largely restricted to damp environments and are inconspicuous
  2. Reproduction a. Sporic type life cycle; true alternation of generations 1) Archegonia and antheridia are produced on the haploid gametophyte b. Asexual Gemma cups, containing small, ovoid gemmae, can be found on the upper surface of some liverwort gametophytes; gemmae may separate and grow into new gametophytes
  3. Asexual reproduction can also occur by thallus branching and growth; the individual thallus lobes elongate and becomes a separate plant when the older thallus dies

B. Phylum Bryophyta (the mosses)

  1. Structure a. Begins as a filamentous green thread, the protonema, that grows from a spore b. From the protonema grows an erect, green, stemlike organ to which are attached a spiral whorl of leaf-like structures (haploid gametophyte generation); no true stems nor leaves (lacks vascular tissue) c. From the base of the stem extend many colorless, hairlike rootlets called rhizoids (not true roots) d. Size of mosses limited to a height of 15 to 20 cm, due to the absence of true vascular and supporting tissues and the inefficiency of rhizoids as water absorbers
  2. Reproduction a. Sex organs develop at the top of the gametophyte stem in the middle of the leaf whorl. b. Some species are dioecious (separate sexes), while others are monoecious (individual containing sex organs of both sexes). c. Sperm produced in the antheridium (sausage-shaped) are spirally coiled and swim utilizing two flagella. d. A rain or heavy dew triggers the sperm release and allows for a medium on the plant by which the sperm may swim to the female sex organ, the archegonium (flask-shaped containing one large egg), either on the same plant or on another one (archegonium releases a chemical to attract the sperm).

bio1120_bryophytes 3/17/

e. The sperm swims down the archegonium's neck to fertilize the egg producing a zygote (beginning of the diploid sporophyte generation). f. The sporophyte is a leafless, single, spindle-shaped stalk (seta), living in its later life as a parasite on the independent gametophyte (obtains most of its nourishment by means of a foot that grows down into the gametophyte tissue, although the sporophyte is capable of photosynthesis in young plants). g. The capsulated sporangium forms at the upper end of the sporophyte stalk where meiosis occurs to produce haploid spores (beginning of the gametophyte generation) released into the air.

  1. Ecologically, are pioneer organisms (first to colonize very demanding habitats) and act as sponges to hold water in wet ecosystems like bogs, marshes, and swamps as well as preventing erosion.
  2. Sphagnum used as packing material for live plants and in plant landscaping because of water absorbing properties; sphagnum remains form peat, which is used as fuel in many countries.
  3. Phylogenetically, relationship to the filamentous algae because of the protonema's resemblance.

C. Phylum Anthocerotophyta (the hornworts): may or may not be closely related to other bryophytes

  1. Description a. gametophytes superfically resemble the thalloid liverworts b. their cell structure with the presence of a single large chloroplast greatly resembles certain algae, while mosses and liverworts contain many disk-shaped chloroplasts c. the sporophyte generation projects out of the gametophyte tissue, forming a horn-shaped spike after fertilization.

II. Bryophytic Phylogeny A. Fossil Record

  1. Bryophytes may have arisen from ancestral green algae at a different time than did early vascular plants, or mosses may have descended from early vascular plants by becoming simpler and losing their vascular tissue
  2. Bryophyte evolution is still unclear