BELL, NEIL E.1,2* and ANGELA E. NEWTON1. 1Department of Botany, Natural History Museum, Cromwell Road, London, SW7 5ED, U.K.; 2The Centre for Plant Diversity and Systematics, School of Plant Sciences, The University of Reading, Whiteknights, Reading, RG6 6AS, U.K.. - Phylogenetic studies of the Rhizogoniaceae (Bryales): unravelling the origins of pleurocarpy.
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