Evolutionary grade
Bryophytes were long considered a natural group, defined as those land plants which lacked vascular systems. Molecular evidence shows that the bryophytes are not monophyletic since mosses, liverworts and hornworts are in fact separate lineages, with mosses closest to vascular plants.  However, the three clades have a similar degree of complexity, and the "bryophyte grade" is a useful benchmark when analysing early plants  it gives information about the status of fossils which cannot always be classified into living groups.