The range of possible morphologies for any given lineage of plant is constrained by itís phylogenetic history. Mosses are relatively simple plants, with correspondingly few structural elements available to provide the units of different branching architectures. Consequently, phylogenetically diverse moss lineages may have superficially similar growth forms, such as dendroid, pendulous, or weft forming. For example, dendroid growth forms, with an upright "stipe" and spreading branches, appear to have developed independantly in at least the Climaciaceae, Hypnodendraceae, Pilotrichaceae, Pterobryaceae and Thamnobryaceae. In this study, representatives of different lineages were dissected out, and the branching architecture analysed. Relatively few structural elements were found to interact in different combinations to result in the observed growth forms. In the case of dendroid mosses the growth form results from the interaction of characters relating to termination and origin of the primary module, "stipe" orientation (where a stipe may be a primary or secondary module), origin, density and plane of secondary modules, formation of a stolon, and reiteration. The distribution of the states of these characters was examined on a phylogenetic tree derived from molecular and morphological data. Although the states of some of these characters were found in several different lineages that are not closely related (based on this tree), others were restricted to monophyletic lineages. In the pleurocarpous mosses, release from morphological constraints through innovations in orientation, branching and modularity have permitted the development of a wide range of different growth forms.

Key words: branching architecture, mosses, phylogeny, pleurocarps