Datiscaceae Revisited: Monophyly and the Sequence of Breeding System Evolution

Abstract

Previous studies of the small angiosperm family Datiscaceae have drawn contradictory con- clusions regarding its monophyly. Clarification of the relationships among the family components is critical to the interpretation of breeding system evolution within this family. Datisca glomerata is the only androdioe- cious member of the otherwise dioecious family and an initial phylogenetic study suggested that this rare breeding system was derived from dioecy in this family. A subsequent, broader scope phylogenetic analysis of Datiscaceae and related families has since suggested that Datiscaceae are not monophyletic, calling into question earlier conclusions regarding the evolution of androdioecy in Datiscaceae. In the present study, the phylogenetic relationships of Datiscaceae and the sequence of breeding system evolution are reexamined. DNA sequences from three sources including nuclear 18S ribosomal DNA, the internal transcribed spacer (ITS) region of nuclear ribosomal DNA, and the chloroplast-encoded rbcL gene were analyzed phylogeneti- cally using parsimony. Results from analysis of rbcL, 18S, and a combined data set all agree that Datiscaceae do not form a monophyletic assemblage. Datisca appears as a sister group to Begoniaceae in all analyses, but the position of sister taxa Octomeles and Tetrameles relative to Datisca and other members of the Cucurbitales is unresolved. The two species of Datisca form separate monophyletic lineages according to ITS analysis, pro- viding no evidence for a progenitor-derivative relationship for the two species. Phylogenetic trees from analy- ses of rbcL and 18S disagree as to whether dioecy or monoecy is ancestral to Datisca, and thus provide no evi- dence as to which sexual system gave rise to androdioecy in D. glomerata, however, there is no evidence for