Systematics Section / ASPT
Edwards, Erika , Donoghue, Michael J. .
Basal phylogenetic relationships in Cactaceae, and implications for early cactus evolution.
Pereskia (Cactaceae) comprises 17 species of leafy shrubs and trees that have long been thought to approximate the "ancestral cactus". In spite of many previous studies of cactus phylogeny, relationships between Pereskia and other cacti have remained unresolved. Here we present a phylogenetic hypothesis of basal cactus relationships based on DNA sequence data from 4 loci spanning 3 genomes (nuclear phyC, chloroplast rbcL and psbA-trnH IGS, and mitochondrial cox3 intron). These data, particularly phyC, provide strong support for a paraphyletic Pereskia, and successfully resolve the earliest divergence events within Cactaceae. Our data indicate an initial split between a clade of 8 Pereskia species located primarily around the Caribbean basin, and all other members of Cactaceae. The remaining species of Pereskia, with a distribution centered in the central Andes and southeastern South America, are united with the cactoid, opuntiod, and Maihuenia lineages. There is also strong support for a sister relationship between Maihuenia and the Cactoideae. These results suggest that there was an early north-south split in Cactaceae, and that the two major cactus lineages, Cactoideae and Opuntiodeae, both originated in the southern half of South America. A paraphyletic Pereskia also provides a new opportunity to examine early trait evolution within the cacti, and we begin by reconstructing the evolutionary history of several key anatomical features that may have been important in the evolutionary transition to stem-based photosynthesis.
1 - Yale University, Department of Ecology and Evolutionary Biology, P.O. Box 208105, New Haven, Connecticut, 06520-8105, USA
Presentation Type: Paper
Location: Cottonwood C (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 3:15 PM