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Some Cytotaxonomic Problems in the Crassulaceae

Charles H. Uhl
Evolution
Vol. 15, No. 3 (Sep., 1961), pp. 375-377
DOI: 10.2307/2406235
Stable URL: http://www.jstor.org/stable/2406235
Page Count: 3
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Some Cytotaxonomic Problems in the Crassulaceae
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Abstract

Cytological study of over 500 taxa of the Crassulaceae has revealed several general problems. First, intraspecific heteroploidy is rather frequent, with some species, as generally conceived, having as many as five or more chromosome races that differ by polyploidy and/or aneuploidy. Morphological variation within the species is not always closely correlated with the differences in chromosome number. The frequency of such incipient species suggests rapid evolution. Second, some genera are extremely diverse cytologically, with no one basic or ancestral number evident. Other genera are cytologically more homogeneous. This difference in stability of chromosome number must be genetically controlled and apparently reflects different modes of speciation. Third, extremely high chromosome numbers are rather common, with gametic numbers exceeding 150 known in six Mexican and South American species. Chromosomes of these species are very small, but the available evidence suggests they arose as true polyploids and not as a result of fragmentation.

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