The allopolyploid origin of Sedum rupestre subsp. rupestre (Grassulaceae)
't Hart, H., Sandbrink, J. M., Csikos, I., Van Ooyen, A., and Van Brederode, J. (1993). Pl. Syst. Evol. 184: 195-206. [Full text: PDF]
In Sedum rupestre L., a polyploid series (x=16) occurs in which aneuploid chromosome numbers and odd levels of ploidy prevail. The most common and widely distributed cytotype, S. rupestre subsp. rupestre, is 2n=112.
Plants resembling S. rupestre subsp. rupestre can be obtained by hybridizing the tetraploid cytotypes of S. forsterianum Sm. (2n=48) and S. rupestre subsp. erectum 't Hart (2n=64). Comparison of these artificial hybrids with their parents and a large number of plants of S. rupestre subsp. rupestre (2n=112) from nature showed that S. rupestre subsp. rupestre and the artificial hybrids are morphologically indistinguishable and intermediate between S. forsterianum and S. rupestre subsp. erectum. Morphologically, S. rupestre subsp. rupestre is closer to subsp. erectum than to S. forsterianum. Chloroplast DNA restriction patterns of S. rupestre subsp. rupestre, however, resemble S. forsterianum more closely.
The combined results of the hybridization experiments, the analysis of the cpDNA restriction patterns, and the morphological variation indicate the allopolyploid origin of S. rupestre subsp. rupestre.