We had already expressed our doubt that Frailea horstii F. Ritter was really different from Frailea gracillima (Lemaire) Britton & Rose in the publication on our website in 2010, in the comments about the two taxa, while accepting that the first taxon as a good species. Subsequent surveys on the habitat of F. horstii, conducted in 2011, confirmed those doubts, pointing out that this is only one population of F. gracillima with more ribs: 20-33 vs 14-22, and more spines: 3-6 central and 15-20 radial vs. 2-5 central and 8-13 radial. The distribution of F. horstii, located in the zone of Caçapava do Sul, Rio Grande do Sul (BR), is included in the widespread F. gracillima. For these reasons we will include F. horstii among the synonyms of F. gracillima. (Quoted from: Anceschi & Magli 2013b, 55)