Studies on Mexican Cactaceae. VII. Taxonomic Notes on Disocactus heterodoxus

Disocactus heterodoxus is a poorly known species from Guatemala and Mexico. It has been treated in the taxonomic literature as a subspecies of D. speciosus or as a synonym of D. speciosus subsp. cinnabarinus. We present a detailed morphological description of this plant and synthesize the available data on its habitat and geographic distribution. In addition, we discuss its taxonomic affinities with other members of Disocactus. Based upon its unique combination of morphological characters (flat, 2-ribbed stems with few or no spines, and narrowly infundibuliform flowers with colors ranging from white to pink and red) and on published molecular data, we believe that there is sufficient evidence to recognize this plant as a distinct species.