Turbinicarpus

Turbinicarpus is a genus of very small to medium-sized cacti, which inhabit the north-eastern regions of Mexico, in particular the states of San Luis Potosí, Guanajuato, Nuevo León, Querétaro, Hidalgo, Coahuila, Tamaulipas and Zacatecas.

==Taxonomy== The taxon was first proposed by Curt Backeberg as Strombocactus subgenus Turbinicarpus. It was elevated to a genus in 1937 by Franz Buxbaum and Backeberg. The circumscription of Turbinicarpus has been described as "remarkably unstable", with species regularly transferred to other genera. Its taxonomic history is often mixed with that of other genera like Echinocactus, Echinomastus, Gymnocactus, Mammillaria, Neolloydia, Normanbokea, Pediocactus, Pelecyphora, Strombocactus, Thelocactus and Toumeya, as the results of almost two centuries of constant evolution in the understanding of the affinities and relationships inside the family Cactaceae. A genus revision by Davide Donati in 2003, and again in 2004 with Carlo Zanovello, was based on a wide range of characters. At the end of that study, Rapicactus was considered a distinct genus from Turbinicarpus. The genus Turbinicarpus was subdivided in two subgenera at the light of the results of the DNA analysis, and into many series because of the ontogeny of the spination. The broad circumscription of Turbinicarpus was recognized as polyphyletic by Hunt in 2016. A phylogenetic study published in 2019 showed that both Kadenicarpus and Rapicactus were distinct from a more narrowly circumscribed and so monophyletic Turbinicarpus: