Guy Nesom published a five-part revision of Heterotheca section Chrysanthe in October 2020 in the journal Phytoneuron. My past experience is that Nesom is usually correct, or at least much less wrong than others. So, since his revision of Heterotheca section Chrysanthe came out, I’ve been meaning to go through it in some detail. I think I’ve more or less got my head around it now and, foolhardy though it may be, I’ve attempted a key to New Mexico Heterotheca based on Nesom’s treatment. There are intermediates between any species that occur together, near as I can tell, so even in the best case there’s a limit to how high a success rate one might expect from keying them. How much worse the success rate is likely to be with my draft key, I prefer not to guess. In any case, it might work and you can download it here.

Of course, after tackling New Mexico, I got carried away. So, here’s a key for Arizona, a key for Colorado, a key for Kansas, one for Nevada, one for Utah, a key for the northern Great Plains, a key for the northwestern United States, and a key for Wyoming.