Abstract
The morphology and chromosome number of nine species of Cirsium of eastern North America are considered. Chromosome counts are presented for the first time for C. iowense, 2n = 18; C. lecontei, 2n = 32; C. nuttallii, 2n = 24, 28; C. repandum, 2n = 30; C. smallii, 2n = 34; C. engelmannii, 2n = 20; C. texanum, 2n = 22, 24; C. virginianum, 2n = 28. Additional chromosomes, possibly to be considered as accessories, were found in C. nuttallii, C. engelmannii, and C. texanum. These chromosomes render uncertain the number characteristic of these species. A key to the 26 native and introduced species found in Canada and the United States east of 100° west latitude is presented. The interrelationships of the eastern species and of the species of the western series Undulata are discussed.
Published Version
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