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Analyses of cpDNA matK sequence data place Tillaea (Crassulaceae) within Crassula |
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| Authors: | Mark Eugene Mort Christopher P Randle Priscilla Burgoyne Gideon Smith Ernst Jaarsveld Stephen D Hopper |
| Institution: | 1. Department of Ecology and Evolutionary Biology, The Natural History Museum and Biodiversity Research Center, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS, 66045-7543, USA 2. Department of Biological Sciences, Sam Houston State University, 1900 Avenue I, Huntsville, TX, 77340-2116, USA 3. National Herbarium, South African National Biodiversity Institute, Private Bag X 101, Pretoria, 0001, South Africa 4. Department of Environmental Sciences, College of Agriculture and Environmental Sciences, UNISA, P.O. Box 392, Pretoria, 0003, South Africa 5. Biosystematics Research and Biodiversity Collections, Private Bag X 101, Pretoria, 0001, South Africa 6. H.G.W.J. Schweickerdt Herbarium, Department of Botany, University of Pretoria, Pretoria, 0002, South Africa 7. Kirstenbosch Botanical Garden, Rhodes Avenue, Newlands, Cape Town, South Africa 8. Royal Botanic Gardens, Kew, Richmond Surrey, TW9 3AB, UK |
| Abstract: | Analysis of cpDNA matK sequences for a total of 43 members of the succulent plant family Crassulaceae, including 24 taxa of Crassula, recovered a well-supported clade comprising Crassula species that is sister to the remainder of the family. The resulting topologies do not support the monophyly of the currently recognized subgenera of Crassula, as one member of subgenus Disporocarpa (C. crenulata) is placed as sister to an otherwise monophyletic subgenus Crassula. The major synapomorphy that has been used to recognize the latter subgenus is a base chromosome number of x = 7 versus a base of x = 8 in the other subgenus. We cannot assess the utility of this feature for defining subgenus Crassula because a chromosome count of C. crenulata has yet to be published. The five accessions of the recently resurrected segregate genus Tillaea (of 24 total Crassula species) included here were placed in four separate, well-supported lineages, one of which is greatly removed from the other four accessions. This suggests that this genus is not valid and should not be recognized. An initial examination of the evolution of habit indicates that a perennial habit is ancestral and that the annual habit is a feature that has been derived at least twice in the genus. |
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