Classification of Nonvascular Plants

It is not known how closely related mosses, liverworts, and hornworts are. They have many features in common but also differ in significant respects. They are commonly treated as three distinct divisions: mosses, division Bryophyta; liverworts, division Hepatophyta: and hornworts, division Anthocerotophyta (Table). This classification emphasizes their differences and stresses the need to treat each group individually and study each in its own right.

Alternatively, all three may be grouped together in division Bryophyta as three classes mosses, Musci; liverworts, Hepaticae; and hornworts, Anthocerotae. This emphasizes their similarities and the possibility that all three are closely related. Inaccurate generalizations may result, obscuring the fact that we actually know very little about many of them, particularly hornworts and liverworts. Numerous studies have been made of moss physiology, especially water relations and mineral nutrition, but almost nothing is known of liverwort or hornwort metabolism. Conclusions derived from studies of mosses are some­times applied to liverworts and hornworts because all are "bryophytes." To discourage such generalizations and to encourage studies of all groups, the three groups are treated here as divisions, and the generic term "bryophyte" is used only for mosses. All groups together are called "nonvascular plants."