..... Click the link for more information. (class Bryopsida), the liverworts liverwort, any plant of the class Marchantiopsida. Mosses and liverworts together comprise the division Bryophyta , primitive green land plants (see moss ; plant ); some of the earliest land plants resembled modern liverworts.
..... Click the link for more information. (Marchantiopsida), and the hornworts (Anthocerotopsida). The liverworts and hornworts are generally inconspicuous plants; common liverworts include species of the genera Porella and Marchantia. Anthoceros is the most familiar temperate-zone hornwort genus. Bryophytes differ from ferns, cone-bearing plants, and flowering plants in that they lack a vascular system for the transportation of water. Since their cells must absorb water directly from the air or the ground, nearly all bryophytes grow in moist places.
Bryophyte Generations
The conspicuous green plant body of a bryophyte is the haploid, or gametophyte gametophyte (gəmē`təfīt'), phase of plant life cycles in which the gametes, i.e., egg and sperm, are produced.
..... Click the link for more information. , generation of the plant life cycle. It consists of a small stem with leaflike projections, as in all mosses and most liverworts, or a leafless, flattened body (thallus), as in some liverworts and all hornworts. The plant is anchored by means of threadlike structures called rhizoids. The leaflike structures and the rhizoids lack the complex internal anatomy found in the leaves and roots of plants with vascular systems. The gametophyte reproduces sexually, giving rise to a diploid, or sporophyte, generation; the sporophyte is a structure that grows directly out of the gametophyte and is at least partly dependent on the gametophyte for nourishment.
In mosses, germinating spores (haploid) produce a green filamentous structure on the surface, called a protonema, the first stage of the gametophyte. Erect branches arise out of the protonema. After the branches produce rhizoids, the protonema dies. Antheridia (or sperm-producing structures) and archegonia (egg-producing structures) are borne in clusters on the tips of the branches of the gametophytes; these structures are usually microscopic. The different sex organs may be in a single cluster, in separate clusters on the same branch, or on separate branches, depending on the species. In the hornworts, antheridia and archegonia are borne either on the same thallus or, in some species, on separate thalli; the antheridia are borne either singly or in small groups, and the archegonia are borne singly. In the liverworts, the gametophyte may be a thallus or may be leafy; the antheridia and archegonia are borne on special branches that arise from the leafy stem.
Fertilization and Reproduction
In all bryophytes fertilization is dependent on water—usually a film of water or the splashing of raindrops—for the transfer of sperm to the egg. Chemical stimuli direct the motile flagellate sperm to the archegonium. The fertilized egg (zygote) grows out of the gametophyte, which is also the source of its nourishment. Typically the sporophyte is a slender stalk from 1 to 2 in. (2.5–5 cm) long, with a capsule at the tip; in some species it may be green and manufacture some of its own food. Cells within the capsule undergo meiosis (reduction division) to produce haploid spores. In many mosses the capsule has a lid, the operculum, which is shed, releasing spores. In other bryophytes the mature capsule ruptures in other ways to release spores.
Classification and Importance
The mosses are generally divided into three orders, with the order Bryales most prominent. It is now believed that the bryophytes descended from green algae by way of now extinct ancestors (the Rhyniophyta Rhyniophyta (rī'nēŏf`ətə), division of plants known only from fossils, of which the genus Rhynia
..... Click the link for more information. ). The bryophytes are important because they are pioneer plants and soil builders on surfaces lacking other vegetation. Sphagnum sphagnum (sfăg`nəm) or peat moss, any species of the large and widely distributed genus Sphagnum,
..... Click the link for more information. moss (order Sphagnales) has been economically important as packing material and as peat peat, soil material consisting of partially decomposed organic matter; found in swamps and bogs in various parts of the temperate zone. It is formed by the slow decay of successive layers of aquatic and semiaquatic plants, e.g., sedges, reeds, rushes, and mosses.
..... Click the link for more information. .
Bryophyta
The gametophytes may consist of leafy stems or flat thalli. They have no roots but are anchored to the substrate by hairlike rhizoids. Vascular tissue is at best poorly differentiated, with no lignification of cells. Growth results from the divisions of single cells (rather than meristematic tissues) located at stem tips or in notches at the margins of thalli. The sex organs are multicellular and have a jacket of sterile cells surrounding either the single egg produced in flask-shaped archegonia or the vast number of sperms produced in globose to cylindric, stalked antheridia. The sperms swim by means of two flagella. The sporophyte commonly consists of a capsule that produces a large number of spores, a stalklike seta, and a swollen foot anchored in the gametophyte. The spores, nearly always single-celled, are dispersed in the air, except in the case of a small number of aquatics. They germinate directly or produce a juvenile stage called a protonema. See Reproduction (plant)
A division that consists of some 23,000 species of small and relatively simple plants commonly known as mosses, granite mosses, peat mosses, liverworts, and hornworts (see illustration). The bryophytes display a distinct alternation of sexual and asexual generations; the sexual gametophyte, with a haploid chromosome number, is the more diversified. The sporebearing, diploid sporophyte is reduced in size and structure, attached to the gametophyte, and partially or almost completely dependent on it.
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The division can be divided into five classes: Sphagnopsida (peat mosses), Andreaeopsida (granite mosses), Bryopsida (true mosses), Hepaticopsida (liverworts), and Anthocerotopsida (hornworts). The mosses have radially organized leafy gametophytes that develop from a protonema and have multicellular rhizoids with slanted crosswalls. The liverworts and hornworts are mostly flat and dorsiventrally organized and have no protonematal stage; the rhizoids are unicellular. Though obviously related, as evidenced by similar sex organs and attachment of a simplified sporophyte to a more complex and independent gametophyte, the classes differ greatly in structural detail. See Plant Kingdom
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