A maximum parsimony analysis of a four-gene cpDNA dataset including 55 exemplar taxa indicates that the Rhizogoniaceae plus Aulacomnium and Calomnion are the sister group or nearsister group to pleurocarpous mosses, which with 6600 species is the most diverse clade of extant mosses. The evidence suggests that the traditional genera of Rhizogoniaceae are a paraphyletic group, consisting of a minimum of 3 clades. Aulacomnium is a monophyletic group, and its sister lineage includes Mesochaete. The pleurocarps are comprised of a relatively small "racopilalean" clade and a large "hypnalean" clade (including Hookeriales, Hypnales and Leucodontales), a fundamental division that is consistent with the conclusions by DeLuna et al. and Newton and DeLuna. These results have implications for our understanding of diversification, adaptation, disparity, development, and genome evolution of the pleurocarps. The rhizogonean mosses ---including Aulacomnium and Calomnion --- have a Gondwanan distribution centered in Oceania, where most rhizogonean species have a substrate preference for tree ferns. Altogether this suggests an origin of pleurocarps within Oceania from an epiphytic ancestor during pre-Cretaceous time. The rhizogonean mosses should be given high conservation priority because of their phylogenetic position and because they have low species richness compared to pleurocarps.

Key words: Aulacomnium, pleurocarpous mosses, Rhizogoniaceae