ABSTRACT
In this chapter, the authors present a discussion of several of the critical questions. Can peristomial features resolve the relationships of the arthrodontous peristome types? What contribution can be made by molecular data to resolving the higher relationships within mosses? Can a 'next generation' classification at the ordinal rank be developed in major floristic treatments? A 'next generation' classification of the mosses recognizes clades with orders in four subclasses of Arthrodontous mosses. The authors argue that three peristome types independently evolved from a Funaria-type peristome which is characterized by a 4:2:4 cell pattern, a thin OPL, no cilia, an IPL with all symmetric divisions, the presence of an exostome and an opposite arrangement of segments. Crosby proposed that the haplolepideous peristome may in fact be derived from the diplolepideous type, and suggested that in classifications of mosses, the haplolepideous groups should come second, rather than first, indicating their more advanced nature.
