Karyotypes of metaphase chromosomes in diploid populations of Dendranthema zawadskii and related species (Asteraceae) from Korea: diversity and evolutionary implications.

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Although the Dendranthema zawadskii complex has been known to comprise a series of polyploids (4x, 6x, 8x), we found diploid individuals (with 2 n=18) to occur in four populations of D. zawadskii var. latilobum in the southern region of Korea. Karyotypes of metaphase chromosomes were diverse because numbers of metacentric, submetacentric, and acrocentric chromosomes differ even within a population. A total of 17 karyotypes were found in 31 diploid individuals collected from the four populations. The karyotypes were also diverse in the presence or absence of chromosomes with a secondary constriction on a short or long arm and, if present, in the number of such chromosomes. They were further diverse in the presence or absence of non-homologous chromosome(s), the presence or absence of a chromosome with a satellite, and, if present, how many and where satellites are present. Almost the same pattern of diversity was found in diploid individuals (with 2 n=18) of D. boreale and D. indicum as well, irrespective of whether they occur together with D. zawadskii var. latilobum or not. Structural features of chromosomes in the variously different karyotypes suggest that reciprocal translocation and the hybridization between individuals with different karyotypes had repeatedly occurred not only in D. zawadskii var. latilobum, but also in D. boreale and D. indicum. Morphologically intermediate individuals between D. zawadskii var. latilobum and D. indicum suggests that the hybridization occur with different species as well.