Astrophytum myriostigma Lem is an endemic Mexican cactus showing polymorphism that has led previus authors to assign taxonomic classifications based just on external morphological variation or vernacular synonyms. In 2009 we studied a population of A. myriostigma in Sierra El Sarnoso, Durango, Mexico to establish morphotypes and to determine if they are related to differences in elevation, slope, mountain orientation and number of nurses. We tested whether or not the environment modifies the external form of this cactus. We established three morphotypes: cupuliform, conical, and depressed. We examined the relationship between morphotypes and the four environmental variables by discriminant analysis. There was significant difference between morphotypes perimeter means. Also we obtained significant correlations between morphotypes and environmental variables, mainly with slope and slope orientation.