[Wikipedia] Taxonomy: The first description as Opuntia echinocarpa by George Engelmann and John Milton Bigelow was published in 1856. Frederik Marcus Knuth placed the species in the genus Cylindropuntia in 1936. Further nomenclature synonyms are Cactus echinocarpus (Engelm. & J.M.Bigelow) Lem. (1868) and Grusonia echinocarpa (Engelm. & J.M.Bigelow) G.D.Rowley (2006). (link added by Mary Ann Machi)
Calflora:
Information on California plants for education, research and conservation,
with data contributed by
public and private institutions and individuals.
[web application]. 2025.The Calflora Database
[a non-profit organization].Available:
https://www.calflora.org/(Accessed: 03/29/2025).