PHYLOGENETICS AND DIVERSIFICATION OF COTYLEDON (CRASSULACEAE) INFERRED FROM NUCLEAR AND CHLOROPLAST DNA SEQUENCE DATA Botanical Garden staff for providing plant materials and Jenny Archibald for field assistance

Abstract

Crassulaceae includes approximately 35 genera and 1500 species of leaf and stem succulent flowering plants. The family is nearly cosmopolitan in distribution, but is particularly diverse in southern Africa, where five genera comprising approximately 325 species are found. One of these genera, Cotyledon, includes 10 species that are largely confined to South Africa, where they are commonly found on rocky hillsides, coastal flats, and cliff faces. Species of Cotyledon are characterized by five-parted, pendulous, sympetalous flowers, but the genus is highly diverse in growth form, flower color and size, and leaf morphology. One particularly variable species, C. orbiculata, has been divided into five varieties based on leaf morphology and biogeography; however, the monophyly of this species as well as the relationships among the varieties have not previously been investigated. Parsimony analyses of a combined data set of DNA sequences from chloroplast and nuclear genome provided the first estimate of phylogeny for Cotyledon, and resulted in two minimum-length trees and a fully resolved phylogeny for the genus. Results indicate that C. orbiculata is not monophyletic and suggest the need for additional studies and a revised classification within the genus. The flowering plant family Crassulaceae includes approxi-mately 1500 species of leaf and stem succulent herbs and small shrubs within 35 genera. Most members of the family possess five-parted, apopetalous, actinomorphic flowers with 10 sta-mens in two whorls; however, this general floral pattern varies, with some genera having partially to completely fused petals and one genus, Crassula, having only five stamens (i.e., hap-lostemonous). The family is widespread and nearly cosmo-politan in distribution, but centers of taxonomic diversity are found in Macaronesia, Mexico, and southern Africa. Several recent phylogenetic studies on Crassulaceae using chloroplast DNA RFLPs (Ham and 't Hart, 1998), matK sequences (Mort et al., 2001), and sequences of the nrDNA internal transcribed spacers (Mort, 2002) and slightly different taxonomic sam-pling have resulted in topologies that are largely congruent. For example, each study strongly supports the monophyly and basal position of the Crassula clade and places this clade as sister to two major clades. The first clade comprises four gen-era from southern Africa and Madagascar: Adromischus, Cot-yledon, Kalanchoe (including Bryophyllum), and Tylecodon (i.e., the Kalanchoe clade of Ham and 't Hart, 1998). The second clade comprises the remainder of the species in the family, including many familiar horticultural plants such as Echeveria, Sempervivum, and Sedum.