Acanthocalycium, Kaktus-ABC: 224, 412. 1936 ["1935"] sec. Schlumpberger 2021
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.
Excluded from Echinopsis by Schlumpberger & Renner (2012); cf. Hunt (2016), CITES Cactaceae Checklist 3rd edition; see also note under Echinopsis.A