Rapicactus mandragora

Name and accepted circumscription

POWO accepts Rapicactus mandragora as a species native to Durango, Coahuila and Nuevo León. The name in Rapicactus was published in 1942, based on the earlier Echinocactus mandragora of 1929. The literature also contains combinations in the genera Gymnocactus, Neolloydia, Pediocactus and Lodia. Turbinicarpus mandragora remains an important historical name for scientific material. [2-WWW]

Two subspecies are accepted, subsp. mandragora and subsp. pailanus. The species circumscription is therefore broader than the single classical population used in earlier comparisons. The 2019 phylogenetic analysis included material identified as R. mandragora, but subsp. pailanus was not sampled. The placement of this material on the tree applies to the sample studied. [2-WWW] [Vázquez-Sánchez et al. 2019, POWO. Vázquez-Sánchez et al., Table 1]

Root and above-ground body

Hinton compared R. mandragora with R. booleanus and R. subterraneus in his 1996 description of the new species. R. mandragora had a tuberously thickened root and a neck similar to the shorter connection in R. booleanus. Its body was globose and above ground. The position of the body relative to the ground distinguished it from the plant with about two thirds remaining in the substrate. [Hinton 1996, p. 64]

In this comparison, the central spines had brown tips and projected approximately perpendicular to the stem surface. There were eight to fourteen radial spines. The flowers were described as white. These data concern the R. mandragora material compared by the author, associated with the classical site in Coahuila. They do not provide a measurement-based characterisation of all populations of the subsequently accepted subspecies. [Hinton 1996, p. 64]

Epidermis and stem interior

In the anatomical study, epidermal cells had an elongated polygonal outline and straight walls separating adjacent cells. The cuticle covering the epidermis was smooth. The microscope images document the surface of the sampled stems, supplementing the characters visible in the external description. [De la Rosa-Tilapa et al. 2019, online version, p. 2, Fig. 1B, 2B]

Concentric druses occurred in the hypodermis. Druses were also recorded in the pith, and the main wood was non-fibrous. Vascular tissues occurred alongside parenchyma in the succulent stem. This combination allows R. mandragora to be compared with other members of the genus at the level of specific layers. Distribution and organ dimensions remain separate morphological characters. [De la Rosa-Tilapa et al. 2019, online version, pp. 2–4]

Seeds in lineage identification

The 2019 analysis of the genus combined plastid DNA with root, fruit, seed and stem characters. It described a tuberculate seed-coat microsculpture and separate positions of the hilum and micropyle for Rapicactus. The hilum is the scar at the seed's attachment point, and the micropyle is the remnant of the opening in the ovule integuments. These small structures helped distinguish the Rapicactus lineage from externally similar turbinicarpuses. [Vázquez-Sánchez et al. 2019, pp. 409, 416–417]

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