Systematics Section / ASPT
Levsen, Nicholas , Mort, Mark E. .
Phylogenetics and evolution of Cotyledon (Crassulaceae) inferred from nuclear and chloroplast DNA sequence data.
Crassulaceae includes approximately 35 genera and 1500 species of leaf-succulent flowering plants. The family is nearly cosmopolitan in distribution but is particularly diverse in southern Africa and Madagascar. Five genera of Crassulaceae comprising approximately 325 species are found in this geographical region. Included among these genera are Crassula (the jade plants), Kalanchoe, Adromischus. Tylecodon, and Cotyledon. The latter four genera have been shown based on matK sequence data to form a strongly supported clade; however, phylogenetic relationships within this clade have yet to be thoroughly investigated in detail. Here we report the results of a phylogenetic analysis of one member of this clade of Crassulaceae, the small primarily South African genus Cotyledon. This genus includes 10 species of herbs or shrubs commonly found on rocky hillsides and cliff faces. Species of Cotyledon differ from most members of the family by having pendulous, sympetalous often showy flowers; the genus also displays a relatively high degree of growth form and leaf diversity. One highly variable member of the genus, C. orbiculata, has been divided into five varieties based primarily on leaf morphology and biogeography, but the monophyly of this species and the relationships among the varieties has yet to be investigated. We employed DNA sequences from the nuclear and chloroplast genome to provide the first estimate of phylogeny for Cotyledon. Our parsimony analyses result in a well-resolved phylogeny and further place the varieties of C. orbiculata in three separate lineages within the genus. These data suggest the need for substantial future investigation on the evolution of Cotyledon and a revision of the classification of the genus.
1 - University of Kansas, Dept. Ecol. & Evol. Biol. and Natural History Museum, 1200 Sunnyside Ave., Lawrence, Kansas, 66045-7534, USA
Presentation Type: Paper
Location: Cottonwood C (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 4:15 PM