Chemnick et al. (1997) state: "Dioon tomasellii was treated by De Luca et al. 1984 as two varieties; var. tomasellii and var. sonorense. To quote from the description, 'Both the vegetative and reproductive characters show in general continuous variation patterns that do not support specific segregation within the range of D. tomasellii but the variation in the populations of Sonora and northern Sinaloa is such to warrant segregating them as a distinct variety.' Apparently the reference to a continuous gradient of patterns was based on conjecture and not observations in the field, as we have examined both living plants and/or herbarium vouchers of nearly all known populations and have found no pattern of continuous variation. Our studies show that the two varieties of D. tomasellii merit recognition at the species level based on: a host of distinct morphological characters that are maintained even in cultivation; the lack of continuous variation between the two varieties; different habitat preferences; and an RFLP analysis by Moretti et al. 1993. A nomenclatural recombination (Dioon sonorense) is proposed."
Jeffrey Chemnick, Timothy J. Gregory and Morales S. Salas. 1997. A revision of Dioon tomaselli (Zamiaceae) from western Mexico, a range extension of D. merolae, and clarification of D. purpusii. Phytologia 83: 1-6.
Last Modified 2017-12-29