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First published as Digitostigma in Cact. Suc. Mex. 47(4): 79 (2002)HUNT, D. Cactaceae Systematic Initiatives,
15(4):1-2; 5-6, 2003 Astrophytum subg. Stigmatodactylus D. Hunt nom. Nov. Astrophytum caput-medusae (Velazco & Nevárez) D. Hunt comb. nov.

"The authors of Digitostigma caput-medusae are to be congratulated on a truely remarkable discovery, but the feeling of our group is that its peculiar habit is not sufficient in itself to justifiy excluding it from Astrophytum, with which it shares unusual and significant features in common, i.e. the floccose indumentum and eccentric (hat-shaped) seeds, as well as having very similar flowers. Although the possibility is not ignored that it could be an ancient intergeneric hybrid, as has been suggested for the origin of Geohintonia, there is no evidence for this at present, and subgeneric rank within Astrophytum seems more appropriate:
Astrophytum subg. Stigmatodactylus D. Hunt nom. nov. Replaced synonym: Digitostigma Velazco & Nevárez, Cact. Suc. Mex. 47(4): 79 (2002).
Type: Digitostigma caput-medusae Velazco & Nevárez l.c. 81-82.

'Digitostigma' not only contraverses Linnaean canons for the formation of generic names but implies that the plant is notable for its finger-shaped stigmas rather than its spotted tubercles, contrary to the authors explicit intention. For this reason the opportunity afforded by the change of rank has been taken to provide an unambiguous name formed according to classical usage.

Astrophytum caput-medusae (Velazco & Nevárez) D. Hunt comb. nov. B:

Digitostigma caput-medusae Velazco & Nevarez l.c. 81-82. Type: Mexico, edo. Nuevo León, [locality withheld], matorral espinoso tamaulipeco, 100-200 m, 28 Aug 2001, Nevárez & Velazco s.n. (UNL 023704, holo.; UNL 023705 iso.)."

Abstract

"We describe a new genus for the cactus family (Cactaceae) that is located in the state of Nuevo Leon, Mexico. We include the description of the new genus and species (Digitostigma caput-medusae) and compare the new genus with the genera Obregonia, Leuchtenbergia and Ariocarpus as well as a morphological comparison with the subtribes Echinocactinae and Thelocactinae in the tribe Cacteae.
A preliminary survey was made to quantify population size and qualitatively assess status in order to determine current threats to the populations of Digitostigma caput-medusae.
A total of 127 individuals were identified in three isolated populations having a left skewed size distribution. We found fruits and flowers and the effect of livestock grazing could be a threat to the populations. The distribution of one population was limited by land conversion. Due to the limited amount of individuals and restricted distribution, this species should be considered as endangered in both national and international
endangered species lists. Further studies are needed to accurately assess the current status of the population and find possible solutions for its conservation."

Copy of the first description can be seen here: http://www.astrobase.de/Stigmatodactylus/Erstbes/Beschreibungen.html