Crassulaceae are a diverse and systematically complex angiosperm family comprising 33 genera and approximately 1,500 species. Members of this family are typically herbaceous, leaf succulents with 4 or 5 - parted actinomorphic flowers. Crassulaceae have long been considered a natural group closely related to Saxifragaceae. Recent analyses of several large, DNA sequence data sets (e.g. 18S rDNA, rbcL, and atpB) representing the diversity of seed plants confirm that the family is monophyletic and a member of the Saxifragales. In contrast, defining natural groups within the family has been extremely difficult due, in part, to the recurrent evolution of adaptations to xeric habitats, as well as extensive polyploidy. The most-recent comprehensive classification of Crassulaceae recognized six subfamilies. However, the monophyly of these subfamilies has been debated based upon morphology, cytology, biogeography, and cpDNA restriction site analyses. Likewise, systematic relationships at the generic level are problematic. For example, Sedum, the largest genus of Crassulaceae, has been referred to as a "dust bin taxon", suggesting it is polyphyletic. In addition, the limits of other genera (e.g. Kalanchoe, Cotyledon ) have been difficult to ascertain. Here, we report the results of our initial phylogenetic analyses of matK sequences representing over 100 species from 27 genera of Crassulaceae. Our analyses reveal six major clades and suggest that five of the six subfamilies currently recognized are polyphyletic. In addition, our data indicate that Sedum, the largest genus in the family, is a grossly polyphyletic assemblage of taxa, confirming the results of cytology and recent molecular analyses. The topology also provides insights into the limits of several other disputed genera, such as Tylecodon, Bryophyllum, and Kitchingia.

Key words: Crassulaceae, matK, systematics