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. |
