Gametophyte Dominance in Hepaticophyta, Anthocerotophyta, and Bryophyta.

The complex Bryophyta traditionally consisted of 3 groups: mosses, liverworts, and hornworts. Recent studies point up the independence of each of these lineages.  With some 16,000 species, this trio of "primitive" plant groups is quite diverse. Mosses and liverworts are moderately diverse, while hornworts are less well represented. While they are most abundant in warm, moist areas such as the tropics and subtropics, bryophytes are also common in arid regions, as well as arctic and alpine areas.

These are the only land plants in which the gametophyte stage is dominant. They also lack true vascular tissues and differentiated leaves, stems, and roots. However,  aerial portions of the gametophytes are flattened as photosynthetic structures analogous to leaves, and some ventral filaments act as anchoring and absorption structures. Gametangia are surrounded by a layer of "sterile cells" which help to prevent desiccation of gametes, but otherwise their reproductive systems are not highly modified.