Crepis is generally recognized by the rosettes of coarse, often pinnately lobed leaves, erect heads, epaleate receptacles, calyculate involucres, yellow corollas, subcylindric or fusiform, ribbed cypselae, and pappi of barbellulate bristles. The taxonomy and evolutionary relationships of Crepis were studied by E. B. Babcock (1947) and his associates. Their work was thorough and important because of the effort to incorporate cytogenetic information in the evolutionary analysis. Extensive survey of chromosome number and karyotype indicated two major ploidy groups in Crepis, corresponding to New World and Old World species complexes. Of the 12 species of Crepis native to North America, 10 are polyploids with x = 11. The core diploid populations commonly occupy discrete ecologic zones and are thought to be entirely distinct from one another, yet they are interconnected by a continuous complex series of intergrading polyploid forms that are partly or completely apomictic (Babcock). The polyploids are of two forms, autopolyploids that are similar to the diploids, and allopolyploids that combine the characteristics of two or more diploid species. The allopolyploid forms of hybrid origin may exhibit the characteristics of multiple parental species and therefore are difficult to classify. Some of the heterogeneous apomictic populations, or groups of populations, have been grouped together and recognized as subspecies; those taxa are often difficult to identify and further study is clearly needed. Despite these difficulties, the subspecific taxa of Babcock were tentatively included in the present study. The Old World species are mostly diploid (n = 3, 4, 5, or 6). Babcock concluded that there was a progressive decrease in the chromosome numbers, from n = 6 to n = 3. Along with the decrease is a corresponding increase in chromosome asymmetry and reduction in chromosome length.