As already expressed in Hunt et al. (2006, text: 57), probably Corryocactus brachypetalus (Vaupel) Britton & Rose is probably only a lowland form of Corryocactus brevistylus (K. Schumann) Britton & Rose. To confirm  this hypothesis, we emphasize that the dimensional elements of the first taxon are included in the second (see Anderson 2001, 183-184; Hunt et al. 2006, text: 57), apart from the deep orange flower in C. brachypetalus, versus yellow in C. brevistylus (ibidem). However, we are aware of the fallability of using floral characters to distinguish taxa, even at a specific level (Ritz et al. 2007; Lendel et al. unpubl. data; Nyffeler et al. unpubl. data, Nyffeler & Eggli 2010, Schlumpberger & Renner 2012, Anceschi & Magli 2013a). The character constituted by the fastigiate branches (i.e. having erect and parallel branches), which should identify C. brachypetalus (Hunt et al. 2006, text: 57), is not always present (see the surveys of Atiquipa, A&M 1155, A&M 1159, A&M 1164), and moreover it is also found among the populations of C. brevistylus (see the populations of Cabanaconde, A&M 216). For the comparison of the semaphoronts (Hennig 1966, 6-7, 32-33, 63, 65-67) between the two taxa, see:

a) fastigiate branches - A&M 216, (C. brevistylus), Peru, Arequipa, Cabanaconde, Cañon del Colca (photos 1-2), with A&M 1140 (C. brachypetalus), Peru, Arequipa, north-east of Matarani, 511 m (photos 6-8, 10, 20, 22);

b) detail of the ribs - A&M 216, (C. brevistylus), Peru, Arequipa, Cabanaconde, Cañon del Colca (photo 3), with A&M 1140 (C. brachypetalus), Peru, Arequipa, north-east of Matarani, 511 m ( photo 21).

Furthermore, the difference between the green-yellow fruit of C. brachypetalus versus the olive-green of C. brevistylus highlighted in Hunt et al. (2006, text: 57), is not a distinctive enough diagnostic feature of the two taxa, and in fact C. brachypetalus can bear both green-yellow fruit (A&M 1155, photo 29), and olive-green as C. brevistylus (A&M 1140, photo 09). Based on the above, we believe it is correct to attribute the populations of C. brachypetalus to C. brevistylus. (Quoted from Anceschi & Magli 2021, 46)