A phylum containing some 15 000 known species of simple plants possessing no vascular tissue and rudimentary rootlike organs (rhizoids). They grow in a variety of damp habitats, from fresh water to rock surfaces. Some use other plants for support. Mosses show a marked alternation of generations between gamete-bearing forms (gametophytes) and spore-bearing forms (sporophytes): they possess erect or prostrate leafy stems (the gametophyte generation, which is haploid); these give rise to leafless stalks bearing capsules (the sporophyte generation, which is diploid), the latter being dependent on the former for water and nutrients. Spores formed in the capsules are released and grow to produce new plants.
Formerly, this phylum also included the liverworts and hornworts, now regarded as separate phyla (see hepatophyta; anthocerophyta) and the mosses were classified as a class (Musci) of the Bryophyta. The term ‘bryophytes’ may still be used, erroneously, to refer to members of all three phyla.
http://bryophytes.plant.siu.edu/ A resource devoted to mosses, liverworts, and hornworts from Southern Illinois University Carbondale