bryophyte - Bryophyte classification, Bryophyte sexuality

A spore-bearing, non-vascular plant belonging to the division Bryophyta, which includes some 25 000 species of moss, liverwort, and hornwort. Bryophytes have conducting cells but lack true vascular tissue; they have rhizoids, thread-like outgrowths which anchor the plant and conduct water, but no true roots. Leaves, if present, are simple structures, usually one cell thick, with a slightly thicker central strand. The dominant generation is the gametophyte, consisting of either a thallus or a small, leafy plant. The gametes are produced in antheridia (male) and archegonia (female), borne either directly on the surface of the plant or on erect, fleshy-stalked, and often complex structures called gametangiophores. The sporophyte generation consists simply of a long-stalked spore capsule growing directly from a fertilized archegonium. It is very short-lived, and is so dependent on the gametophyte that it is termed parasitic. Asexual reproduction can also occur by means of gemmae - multicellular dics or filaments produced in special cups, either on leaf tips or on stalks (pseudopodia), and able to grow into new plants in the same way that small bulbs of flowering plants do. Bryophytes are mainly terrestrial plants, often epiphytic, but very vulnerable to desiccation, and require water for the transfer of gametes from antheridium to archegonium; they are mostly restricted to damp or humid habitats. They are increasingly regarded as important indicator plants (eg in pollution studies). (Division: Bryophyta.)

The bryophytes are those embryophyte plants ('land plants') that are non-vascular: they have tissues and enclosed reproductive systems, but they lack vascular tissue that circulates liquids.

Bryophyte classification

The bryophytes do not form a monophyletic group but consist of three groups, the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses). In one of these patterns, the liverworts were the first to diverge, followed by the hornworts, while the mosses are the closest living relatives of the polysporangiates (which include the vascular plants). In the other pattern, the hornworts were the first to diverge, followed by the vascular plants, while the mosses are the closest living relatives of the liverworts.

Bryophyte sexuality

These plants are generally gametophyte-oriented; There are two basic categories of sexuality in bryophytes:

Dioicous bryophytes produce only antheridia (male organs) or archegonia (female organ) on a single plant body. Monoicous bryophytes produce both antheridia and archegonia on the same plant body.

Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte plant bears one or both kinds of gametophyte.