Systematics Section / ASPT
Mort, Mark E. .
Molecular phylogenetics of the jade plants (Crassula, Crassulaceae) inferred from chloroplast and nuclear DNA sequences.
The angiosperm family Crassulaceae comprises approximately 1500 species of leaf-succulent herbs and small shrubs. Defining natural (i.e. monophyletic) groups within the family has been notoriously difficult, which is due in part to the high degree of convergence in morphological features often associated with the xerophytic habitats in which these species exist. Broad phylogenetic analyses of Crassulaceae based on cpDNA RFLPs and sequences from both the chloroplast and nuclear genome recover seven major lineages within the family. The basal-most lineage of Crassulaceae comprises the large and diverse genus Crassula (including Tillaea). Crassula comprises approximately 150 species that display a remarkable degree of floral, cytological, anatomical, and growth form diversity. The genus includes species that display an annual, biennial, and perennial habit and members of the genus range from small herbs, to large shrubs and small trees. In part this diversity has contributed to the sordid taxonomic history of Crassula. In fact, this single genus represents a microcosm of the morphological diversity and degree of systematic uncertainty found throughout Crassulaceae. The most recent monograph of Crassula recognized 20 sections placed within two subgenera. However, to date, there has been no comprehensive phylogenetic study of the genus and the monophyly of these sections and subgenera have yet to be tested. To reconstruct phylogeny for Crassula, the trnL-trnF chloroplast spacer region and the nrDNA internal transcribed spacer regions were sequenced for represents of most sections of the genus. Parsimony analyses of these data provide a well-resolved topology and suggest that the two recognized subgenera are monophyletic; however, these analyses also clearly illustrate that many of the sections recognized in Crassula are not monophyletic.
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: 4:00 PM