Content area
Abstract
Cytological investigation of the Cirsium species of Nebraska revealed chromosome numbers that correlated with morphological circumscription of the taxa. The chromosome numbers of these species were generally in agreement with those reported in the literature. Most of the variability within the taxa was probably due to an interplay of genetical and environmental influences and not to differences in chromosome numbers. The occasional presence of extra chromosomes in a few taxa may also contribute towards phenotypic variations. Morphological complexity within a few taxa is compounded by hybridization. One instance, involving Cirsium undulatum and Cirsium flodmanii, is the first report of its kind anywhere. Another instance, involving Cirsium altissimum and Cirsium discolor, represents a first report for Nebraska.
