Rapicactus

(Halda & Panar.) M.H.J.van der Meer

The most widely distributed species in the genus, also occurring high in the mountains of northeastern Mexico. Comparative studies included the nominate subspecies and subsp. hintoniorum. Its habitats range from limestone substrates to cooler sites with humus.

A cactus from the gypsum hills of Nuevo León, with most of its body and its neck hidden underground. Its thickened root, numerous white radial spines and magenta flowers were described in the original 1996 publication as Turbinicarpus booleanus.

A species with a thickened root and globose body, also called Turbinicarpus mandragora in earlier accounts. The species name now includes the nominate subspecies and subsp. pailanus. Its above-ground structure differs from that of the partly buried Rapicactus booleanus.

A cactus with a thickened root joined to the above-ground part by a narrow section. Formerly described as Turbinicarpus subterraneus. Anatomical studies distinguished it by few fibres in the main xylem and xylem surrounded by phloem in cortical bundles.

A species from Nuevo León and Tamaulipas, historically also included within Rapicactus subterraneus. In microscopic studies it was distinguished by a single-layered hypodermis and cork structure different from the alternating layers of the other Rapicactus examined.