Populations of Argyrochosma limitanea represent two morphologically distinctive taxa treated here as subspecies. For the most part, these taxa have different geographic ranges, and genetic interaction between them is precluded because both are asexual triploids. Isozyme analyses indicate that the two subspecies have different polyploid origins, but evolutionary relationships (and proper taxonomic treatment) cannot be resolved until sexually reproducing (64-spored) progenitors are found.