''Rapicactus'' is a genus of cactus in the tribe

Cacteae Cacteae is a tribe of plants of the family Cactaceae found mainly in North America especially Mexico. , the internal classification of the family Cactaceae remained uncertain and subject to change. A classification incorporating many of the insi ...

, subfamily Cactoideae. It has been synonymized with '' Turbinicarpus'' but

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies have supported its monophyly and separation from that genus.

Taxonomy

The genus ''Rapicactus'' was proposed in 1942 by Buxbaum and Oehme. It was characterized by having thick roots with a constriction above forming a neck. However, most subsequent treatments sank the genus into a broadly

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...

genus ''Turbinicarpus''. The circumscription of ''Turbinicarpus'' has been described as "remarkably unstable", with species regularly transferred to other genera. The broad circumscription of ''Turbinicarpus'' was recognized as polyphyletic by Hunt in 2016. A phylogenetic study published in 2019 showed that a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

''Rapicactus'' was sister to ''

Acharagma ''Acharagma'' is a genus of two cactus species from northern Mexico. Description These cacti are usually solitary but sometimes occur in small clusters. The globose stems tend to be about 3–7 cm in diameter. The ribs have tubercles, wit ...

'', separated from a monophyletic ''Turbinicarpus'':

Species

Plants of the World Online Plants of the World Online (POWO) is an online database published by the Royal Botanic Gardens, Kew. It was launched in March 2017 with the ultimate aim being "to enable users to access information on all the world's known seed-bearing plants by ...

accepted four species:

References

Cactoideae Cactoideae genera {{Cactus-stub