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Bryophytanonvascular

plants

Psilopsidavascular

plants

(Gr. bryon: moss; phyton: plant).

BRYOPHYTA

A division of nonvascular plants, mainly terrestrial in habitat containing about 25 000 species. It comprises the three classes *Hepaticae (liverworts), *Musci (mosses), and *Anthocerotae (hornworts). Bryophytes are generally small low-growing plants, in most cases susceptible to desiccation and hence limited to damp or humid environments.  

Their life cycle shows a heter-omorphic alternation of generations with the haploid gametophyte, which may be homo- or heterothallic, the dominant generation. The ephemeral sporophyte is partly or completely parasitic on the gametophyte and consists solely of a stalk bearing the spore capsule.

Certain similarities between mosses and algae, especially between algal filaments and the moss *protonema, suggest that bryophytes evolved from algae, most probably green algae, since these also share similar photosynthetic pigments, food reserves, and cell-wall constituents.

Bryophytes however exhibit considerably greater morphological differentiation than the algae and differ also in producing aerial spores and having enclosed sex organs. Nevertheless they still lack roots and water is needed for the dispersal of antherozoids and for fertilization.

Despite their primitive characteristics, bryophytes are the dominant vegetation in certain areas, notably the bogs of temperate latitudes.

PSILOPSIDA

Psilotum (whisk fern) is a genus of fern-like vascular plants,

A subdivision or class of *vascular plants containing two living genera, Psilotum and Tmesipteris, that together constitute the order Psilotales. The fossil forms, which are known chiefly from rocks of the Devonian period, are placed in the order Psilophytales. These fossils include Psilophyton and, from the Rhynie chert, Rhynia. The living psilopsids are considered the most primitive of the vascular plants. The sporophyte is dichotomously branching and bears rhizoids rather than true roots.

Small leaflike appendages are often present and the vascular tissue consists of tracheids and poorly defined phloem. The spores, which are homosporous, give rise to a subterranean gametophyte. Fertilization of the gametes relies on the presence of a film of water and embryogeny is exoscopic. In some classifications the living and fossil forms are separated into two subdivisions or classes, the Psilotopsida and Psilophytopsida respectively.

http://botanydictionary.org/bryophyta.html