Chromosome Numbers in the Compositae. Iv. North American Species, With Phyletic Interpretations

T urner , B. L., W. L. E llison , and R. M. K ing . (U. Texas, Austin.) Chromosome numbers in the Compositae. IV. North American species, with phyletic interpretations. Amer. Jour. Bot. 48(3): 216–223. Illus. 1961.—Chromosome counts from 116 different plant populations representing 75 taxa (72 species in 39 genera) are reported. These include the first species counts for the following genera: Actinospermum ( x = 19), Baltimora ( x =15), Calea ( x = ca. 17, 18), Calyptocarpus ( x = 12), Hecubaea ( x = 17), Lagascea ( x = 17), Schistocarpha ( x = 8), Melanthera ( x = 15), Pectis ( x = 12), Perymenium ( x = 15), Sanvitalia ( x = 8), and Trigonospermum ( x = 15). Chromosome counts for Chrysopsis trichophylla ( n = 5), Cirsium horridulum ( n = 16), Hidalgoa ternata ( n = 16,) Tridax balbisioides ( n = 10), Tridax trilobata ( n = 10), and Verbesina crocata ( n =18) differ from the reported basic numbers as determined from other species in these genera. Taxa closely related to Tridax procumbens were found to have the diploid number n = 9, thus establishing the polyploid nature ( n = 18) of this widespread polymorphic species. When appropriate, the chromosomal information has been related to systematic problems.