Montanucci, Richard R., and Klaus-Peter Kleszewski. “Taxonomic History, Comparative Morphology, and Variation in Astrophytum Myriostigma and Its Subspecies Tulense (Cactaceae)”. Journal of the Botanical Research Institute of Texas 15, no. 2 (December 10, 2021): 327–341. Accessed March 29, 2024. https://journals.brit.org/jbrit/article/view/1152.