Astrophytum coahuilense (Möller) Kayser has had an unsettled taxonomic history since it was originally named as a subspecies of A. myriostigma Lemaire by H Möller in 1927. A review of the systematic and horticultural literature reveals that A. coahuilense has been treated as a variety or synonym of A. myriostigma by botanists in the United States and Mexico but is generally recognized as a distinct species in Germany and other parts of Europe. Recent encyclopedic and regionally significant works treat A. coahuilense as a synonym of A. myriostigma. Previous authors performed hybridization experiments involving the two taxa and reported reproductive isolation between them, but these authors provided little or no quantitative data in support of their observations. The results of my preliminary hybridization experiments are in agreement with these published reports. A. coahuilense and A. myriostigma, when artificially hybridized, failed to set fruit or produced seed that, in most cases, failed to germinate. Furthermore, A. coahuilense and A. myriostigma differ in fruit morphology, mode of fruit dehiscence, and have allopatric geographical distributions of several hundred kilometers. The distinguishing genetic and morphological attributes provide compelling evidence for the recognition of the Coahuila Bishop's Cap as a distinct species.