The Rhizogoniaceae is a predominantly southern hemisphere family of eubryalean mosses with a centre of diversity in Australasia and a distribution pattern suggestive of a late mesozoic Gondwanic origin. Many of the taxa are unusual with respect to character states associated with acrocarpy and pleurocarpy, the normally closely associated suite of secondary pleurocarpous traits being variably present in conjunction with more typically acrocarpous features. Such observations are consistent with recent cladistic analyses which place rhizogoniaceous exemplars in a critical phylogenetic position at the base of the other pleurocarpous groups. In the initial stages of a combined morphological and molecular phylogenetic study of the Rhizogoniaceae, an examination of morphological characters was undertaken within the context of recent redefinitions of pleurocarpy. Observations confirm that the family contains both unambiguously acrocarpous and pleurocarpous taxa according to currently accepted definitions. Preliminary molecular analyses resolve several novel clades, many of which can be supported by morphological synapomorphies, and suggest that the family may represent part of a diverse grade immediately basal to the other pleurocarps. Lack of well supported resolution in the basal nodes of this grade compared with the apical rhizogoniaceous and "true" pleurocarp nodes can be interpreted as evidence for a relatively ancient origin of the former, a differential rate of either molecular evolution or of cladogenesis, or a combination of such factors. Further sampling of both characters and taxa will be required if this level of the phylogeny is to be convincingly resolved.

Key words: molecular evolution, morphology, phylogenetics, pleurocarpy, Rhizogoniaceae