MCDANIEL, STUART F.* AND JON SHAW. Department of Botany, Duke University, Durham NC, 27708. - Morphological change is decoupled from molecular evolution in disjunct populations of Pyrrhobryum mnioides (Hook.) Manuel.
Many morphologically defined bryophyte species show intercontinental
disjunctions, a pattern rare among vascular plants. Morphologically
similar forms in geographically disparate bryophyte populations may
also be genetically similar, as a result of either limited
evolutionary potential or very effective long-distance dispersal.
Alternatively, disjunct populations of bryophytes may be genetically
differentiated, but morphology may be a poor indicator of molecular
evolution. I employed phylogenetic analyses, in conjunction with
morphological studies, to evaluate these two hypotheses in the case of
Pyrrhobryum mnioides, a moss common in moist temperate forests
in Southeastern Australia, Tasmania, New Zealand, Patagonia and Andean
South America. DNA sequence data from the nuclear (ITS and 26S) and
chloroplast (trnL and rps4) genomes indicate that
Australasian and American populations of P. mnioides are
reciprocally monophyletic. The results show evidence of neither
intercontinental gene flow nor depressed levels of molecular
evolution. The morphological analyses support the assertion of Fife
(1995) that populations from the two continental regions are subtly
different.
Key words: Pyrrhobryum mnioides , biogeography, bryophyte disjunction, infraspecific phylogeny