WHEELER, JOHN A. University Herbarium, Jepson Herbarium, and Department of Integrative Biology, University of California, Berkeley, CA 94720-2465. - A phylogenetic analysis of the genus Riccia L. (Marchantiales): volatile morphology
that is not reflected in the underlying genetic history.
Molecular phylogenies of the marchantioid liverwort genus
Riccia were reconstructed using independent nuclear and plastid
data sets in the hope of better understanding relative age,
relationships and character evolution in this taxonomically puzzling
and putatively ancient radiation. Cladistic analyses are based on
three nucleotide sequence alignments: 1) partial nuclear-encoded Large
Subunit rDNA (LSU rDNA), 2) the plastid-encoded trnL-F region and 3) a
data set consisting of combined nuclear and plastid alignments.
Alignment ambiguous regions of each alignment were culled.
Independently-derived strict consensus topologies based on 17-18
species of Riccia representing 5/8 of subgenera and 13/19 of
sections (sensu Schuster 1992) are largely congruent; combining
the data results in a strict consensus tree with even higher overall
bootstrap and decay support. A comparison of the nuclear and plastid
trees reveals that five specific clades are common to both; moreover,
in the combined strict consensus topology, six clades are indicated
with bootstrap support greater than 75%. All analyses (nuclear,
plastid and combined) affirm the biological reality of a monophyletic
Riccia (rooted on outgroups Ricciocarpos and
Oxymitra). Striking morphological divergence within
well-supported terminal clades, suggests a propensity in Riccia
for volatile morphology that is not reflected in the underlying
genetic history; characters emphasized in prior systematic treatments
are apparently unstable and therefore perhaps largely unreliable for
the purpose of discriminating phylogenetically meaningful higher-level
intrageneric taxa.
Key words: character evolution, liverworts, Marchantiales, Riccia, volatile morphology