Echinocactus, Verh. Vereins. Beförd. Gartenbaues Königl. Preuss. Staaten 3: 420. 1827 sec. Vargas-Luna & al. 2018
- =Echinofossulocactus in Gard. Mag. & Reg. Rural Domest. Improv. 17: 317. 1841 syn. sec. Vargas-Luna & al. 2018
- =Emorycactus in Succulenta (Netherlands) 75: 270. 1996 syn. sec. Vargas-Luna & al. 2018
- Type: Emorycactus polycephalus
- =Meyerocactus in Succulenta (Netherlands) 75: 271. 1996 syn. sec. Vargas-Luna & al. 2018
Category B. The genus is monophyletic based on phylogenetic studies that support the clade based on a sufficiently dense or even complete sampling, or support a monotypic genus as a distinct lineage, but do not provide a new taxonomic treatment at the species level. In many cases, older classical taxonomic synopses or a monographic treatment exist for these genera providing a reliable assessment of the species included.
Phylogenetics: Echinocactus turns out to be paraphyletic in recent molecular studies (Bárcenas & al. 2011; Hernández-Hernández & al. 2011; Vázquez-Sánchez & al. 2013), with E. grusonii Hildm. resolved in a separate clade from the remaining four species. Vargas-Luna & al. (2018) showed that Echinocactus s.l. was paraphyletic with Astrophytum nested within, and E. grusonii resolved as sister to Ferocactus. They re-circumscribed Echinocactus to reflect this well-supported topology and also showed morphological characters to recognize two genera, Echinocactus s.s., and Homalocephala. It is clear that the monotypic Kroenleinia grusonii is not a member of Echinocactus, however, its distinction from Ferocactus is not entirely clear. See Kroenleinia. A
A. Majure, L.C. 2021: Revisions of Cochemiea, Consolea, Coryphantha, Cylindropuntia, Cumarinia, Grusonia, Kroenleinia, Leptocereus, Melocactus, Micropuntia, Opuntia. – In: Korotkova N. & al., Cactaceae at Caryophyllales.org – a dynamic online species-level taxonomic backbone for the family. – Willdenowia 51: 251-270