CRAWFORD, DANIEL J.*, DONALD H. LES, ELIAS LANDOLT, REBECCA T. KIMBALL, AND JOHN D. GABEL. Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH 43210-1293; Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269-3043; Geobotanisches Institut ETH Zürichbergstrasse 38, , CH-8044, Zürich, Switzerland. - A phylogenetic study of the genus Wolffiella (Lemnaceae).
The genus Wolffiella (Hegelm.) Hegelmaier, together with the
genus Wolffia Horkel ex Schleid., comprise the subfamily
Wolffioideae of the Lemnaceae (duckweeds). Prior to the treatment of
Landolt in 1986, species had been transferred between the genera, and
several segregate genera were recognized in this subfamily. Problems
with generic delimitation were the result of the few morphological
characters available in these very small and simple flowering plants,
and the relative taxonomic significance assigned features. The most
recent treatment of Wolffiella by Landolt recognized nine
species in three sections, and he described a new species in 1992. The
present phylogenetic study of Wolffiella includes more than
4,600 characters, including flavonoid chemistry, morphology, anatomy,
allozymes, and DNA sequences from two chloroplast genes and three
chloroplast introns. A parsimony analysis of our data provide strong
support for the monophyly of Wolffiella as recognized by
Landolt. The two sections Wolffiella and Stipitatae
likewise enjoy 100% bootstrap support. Landolt recognized two major
lineages within the genus, one consisting of sect. Wolffiella
and another comprised of sect. Stipitatae and the monospecific
sect. Rotundae. There is 100% bootstrap support for these two
groups. Within sect. Wolffiella, the three species W.
gladiata, W. lingulata, and W. olbonga are close
morphologically, have high genetic identities at allozyme loci, and
appear to result from recent speciation. They form a highly derived
clade within the section, which is concordant with recent divergence.
The three species of sect. Stipitatae and sect.
Rotundae, which form one of the two major clades in the genus,
show high similarities at allozyme loci, suggesting relatively recent
speciation in this strictly African lineage. The phylogeny suggests
that the radiation of Wolffiella was from southeastern Africa
into South America, and ultimately to North America.
Key words: duckweeds, Lemnaceae, molecular systematics, phylogeny, Wolffiella