At the end of October 2011 in the area of Guaritas-Minas de Camaquã-Santana da Boavista we studied some populations of Gymnocalycium horstii Buining, a species that is increasingly more difficult to observe in habitat. The taxon is morphologically very similar to Gymnocalycium buenekeri Swales but, for us, not so closely related to the previous one as some believe. G. horstii lives mainly on rocks in grassland, usually in the shade of bushes in grazing land. Conditions are similar to those of Gymnocalycium denudatum (Link & Otto) Pfeiffer ex Mittler. According to the testimony of residents and farmers of the zone, it seems that the scarcity of individuals, rather than the soil conversion into agricultural land, may be attributed to theft by collectors, which has persisted over the years. During the recent surveys (following those of 2008), we found two groups of the taxon in the area of Santana da Boavista. The first consists of a few individuals with single heads of modest dimensions in a zone already recognized in the literature; the second, a new small population, composed also of large specimens: <71 cm in width, with the major stem of 8.2 x 15 cm (h x ø) (A&M 797, photos 16-18). Given the scarcity of the populations in habitat, we find it appropriate to update the assessment of the conservation status as follows:

Braun, P. J. & Esteves Pereira, E. (2001): Vulnerable, VU

Hunt et al. (2006): Data Deficient, DD

Anceschi & Magli (2013): Critically Endangered, CR B2ab(ii,iv,v)

(June 2013)