Croptilon Raf. is a small genus of three annual species native to the southeastern U.S. with a center of diversity in eastern Texas. The genus includes an chromosomal aneuploid series from x=7 to x = 4 (Smith 1966). It has been treated as Haplopappus sect. Isopappus (Hall 1928; Smith 1965 Rhodora 67: 217-238.), but phylogenetically it belongs in subtribe Chrysopsidinae, not subtribe Machaerantherinae. In a cladistic study by Semple and Tebby (1999), Croptilon was closely related to Bradburia and Heterotheca. DNA sequence data also place it close to Heterotheca (Brouillet et al. 2009).
Smith (1981 Sida 9: 59-63) treated the taxa in Croptilon and proposed the following nomenclature:
- C. hookerianum var. graniticum (x = 7)
- C. hookerianum var. hookerianum (x = 6)
- C. hookerianum var. validum (x = 5)
- C. rigidifolium (x = 5)
- C. divaricatum (x = 4)