Phylogenetics and Evolution of Crassula (Crassulaceae)

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The jade plants (Crassula, Crassulaceae) are a group of approximately 200 species of flowering plants that are largely confined to South Africa. These plants, while best known for their highly fleshy leaves, display a great diversity of growth forms, ranging from annuals to long-lived shrubs and trees. Species in this group also display a spectacular diversity of flowers; some species possess tiny star-shaped flowers while others have large tubular flowers. Also noteworthy is the high diversity of chromosome numbers that have been reported for some species of jade plants; however, the significance of this variation has yet to be investigated comprehensively. In South Africa, jade plants occur in many different habitats, with many found on moist cliff faces, whereas others are confined to coastal sand dune habitats. In certain areas of the country (e.g. the Succulent Karoo Desert) these species form a major ecological component of the vegetation. Despite their ecological importance and high level of morphological diversity, the taxonomy of these plants has yet to be studied comprehensively. The proposed research by Dr. Mark Mort of the University of Kansas, with colleagues in South Africa, focuses on this attractive and complex group of plants and has several major goals: 1) Evolutionary relationships among species of jade plants will be determined through comparison of DNA sequences from multiple gene regions. This study will result in a necessary framework for examining the diversity in growth form, flowers, and chromosome numbers. In combination, this will permit an assessment of the boundaries of species within this group of plants and ultimately will assist in determining how many species should be recognized. 2) Floral diversity will be assessed via detailed measurements of approximately 17 morphological traits from field-collected flowers. This will provide important insights into floral change in this genus. 3) The extent of chromosome diversity in jade plants will be documented by conducting extensive chromosome counting. Examination of chromosome diversity in conjunction with the estimate of species relationships will permit an assessment of the importance of chromosome changes in creating the species diversity present in jade plants. South Africa, despite its relatively small size, contains a diversity of plants that is comparable to the more widely publicized tropics. Despite its uniqueness, much of the botanical diversity of this region has yet to be examined. Considering the current and ongoing threat to global biodiversity, areas of concentrated diversity, such as South Africa, require special attention. This work will contribute to graduate education at the University of Kansas and is being conducted in collaboration with botanical researchers in South Africa; the results will be communicated to educators and the general public through informal lectures in the U.S. and in South Africa.