BUTTERWORTH, CHARLES A.* and ROBERT S. WALLACE. Department of Botany, Iowa State University, Ames, Iowa 50011. - Infrageneric relationships in the genus Pereskia (Cactaceae).
Members of the genus Pereskia (17 species) exhibit a number of
plesiomorphic characters for the family Cactaceae such as shrubby
habit, non-succulent or partially succulent leaves, and in some
species, nearly superior ovaries. In addition, the members of this
genus also show a transition from perigynous flowers with
half-inferior ovaries to those species having true receptacular
epigyny (the predominant condition in the Cactaceae). To examine this
and other morphological transitions in the presumably basal cactus
lineages, a well resolved phylogeny was sought to provide the basis
for interpreting anatomical/structural innovations and polarizing
character state changes. Interspecific relationships within Pereskia
were inferred using combined datasets from cpDNA restriction-site
data, together with sequence data from non-coding regions of the
plastid genome, including the psbA-trnH, trnL-trnF and
trnT-trnL intergenic spacers, and the rpl16 intron.
Maximum parsimony analyses netted a well-supported phylogeny for
Pereskia, which identified three major clades, these
corresponding to presumed major migration routes from a central Andean
origin to two centers of diversification: one in central and eastern
Brazil, and the other in southern Central America and the Caribbean.
Phylogenetic evidence for the transition from perigyny in the majority
of Pereskia species to epigyny in P. bleo, P.
portulacifolia, P. ziniiflora and P. quisqueyana was
observed. These taxa constitute a strongly supported monophyletic
clade, suggesting that receptacular epigyny has occurred only once in
the genus. The sister group relationship for the yellow flowered
species of Pereskia (P. aureiflora and P.
guamacho) was also confirmed, despite their widely disjunct
distribution, further suggesting that migration has played an
important role in speciation events within this genus.
Key words: Cactaceae, Pereskia, phylogeny