Chromosome studies: Mexican Compositae.

Chromosome observations reported here from 70 collections representing 65 species from 40 genera of Compositae (mostly Heliantheae) provide taxonomically useful information. First counts for 28 species, including the first count for Psacaliopsis, may prove to be especially interesting in relation to phyletic and taxonomic alignments of the taxa. Of special interest among first reports is 2n = 5 II for Stevia lita; other stevias have x = 11, 12, or 17. Thirteen of our counts differ from prior reports and may also be of particular interest in phyletic and taxonomic contexts.