Synonyms

Cactus placentiformis*, Discocactus alteolens, Discocactus placentiformis ssp. alteolens, Discocactus crystallophilus, Discocactus insignis, Discocactus insignis sensu Buining, Discocactus latispinus, Discocactus multicolorispinus, Discocactus placentiformis ssp. multicolorispinus, Discocactus pseudoinsignis, Discocactus pseudolatispinus, Discocactus latispinus ssp. pseudolatispinus, Discocactus pugionacanthus, Discocactus placentiformis ssp. pugionacanthus, Discocactus pulvinicapitatus, Discocactus latispinus ssp. pulvinicapitatus, Discocactus tricornis
* Basionym

Distribution

Brazil (Minas Gerais)

Conservation status

(4)   Vulnerable, VU B2ab(iii,v)

Comments

Karl Schumann presented Echinocactus placentiformis K. Schumann in Flora Brasiliensis (1890, 4 (2): 246-247) and he considered Discocactus insignis Pfeiffer as a synonym of this. In the original Lehmann’s description of Cactus placentiformis Lehmann (1826), and in the first Pfeiffer publication of D. insignis (1837, 5: 241) clear indications of its location were not provided. In his monographic work on Discocactus Pfeiffer, A. Buining (1980, 71; 89) believes that Schumann made an error in considering the two to be conspecific, and he has no doubt that the plants he found at the foot of the mountains near Grão Mogol between 1972 and 1974 correspond to Pfeiffer’s Discocactus insignis; since this plant is so visible on the sides of the road leading to the town, it could well have already been discovered in 1837. Summarizing their position on the subject (Taylor 1981, 43: 40; Taylor & Zappi 1991, 9: 86), in Cacti of Eastern Brazil (2004, 449-450) Taylor & Zappi argue that Buining wrongly identified the plants found with D. insignis Pfeiffer, and that whilst the latter is correctly regarded as a synonym of Discocactus placentiformis (Lehmann) K. Schumann, the first is rather another taxon namely  Discocactus pseudoinsignis N. P. Taylor & Zappi, which they have already published in Bradleya instead of D. insignis sensu Buining, now a synonym of D. placentiformis. This is because in his description Pfeiffer speaks of a plant with 10 ribs, while D. pseudoinsignis usually has 12-13, and also the illustration of the type subsequently published by Pfeiffer (1839, 19 (1): pl. 15) shows dark pink bract-scales on the floral tube and outer perianth segments, which is characteristic of some forms of D. placentiformis, while D. pseudoinsignis has pale brownish-olivegreen outer segments. It is noteworthy that the same illustration (taken for granted before the 1837 publication) is indicated by the authors as lectotype of D. insignis Pfeiffer among the synonyms of D. placentiformis. We would have some doubt that individuals with 10 ribs could not exist among the populations of Discocactus currently living within the P. E. de Grão Mogol, and especially that the plant illustrated by Pfeiffer (whith at least 12 ribs) could not be considered a possible sample of those that live at Grão Mogol. Moreover, the colors shown by Buining for outer perianth segments of its D. insignis (see below), clearly belong to Pfeiffer‘s illustration. However what interests us has nothing to do with the choice between D. insignis Pfeiffer or D. pseudoinsignis Taylor & Zappi, because it is our opinion that they are synonyms of D. placentiformis, since, in nature, they do not show any significant difference, and that Schumann’s publication of 1890 was already correct. Both, Buining (1980, 89) and Taylor & Zappi (2004, 449-450), speaking of D. insignis or D. pseudoinsignis, cannot help but notice how this is similar and included in the habitat of the variable D. placentiformis; therefore, they must specify the differences between them which, however, can all be denied by the observation in habitat and the literature. Indeed, at the end of his description of D. insignis Buining generically says that the differences with D. placentiformis relate to body and flower of the plant, where the major difference is the size of the seed; while Taylor & Zappi say that D. pseudoinsignis differs from the other taxon by the ribs without tubercles (usually 12-13 ribs), the color of the flowerbuds and of the outer segments of the perianth, the apex of the fruit and finally the size of the seed. Let us see how the features of the Discocactus of Grão Mogol are really distinct from those of other populations of D. placentiformis. The photographic material relating to D. insignis / D. pseudoinsignis (photos 32-47) comes from the P. E. de Grão Mogol.


Ribs.
There is no evidence that the ribs of D. insignis / D. pseudoinsignis cannot be tuberculated. Several mature plants, and not only the oldest, as already noted by Buining (1980, 82), carry well-marked tubercles (photos 36, 45-46). The almost straight and regular ribs, reported by Taylor & Zappi (2004, 449), are rather found in individuals of small and medium-small size, while medium and large plants usually have large, rounded, sometimes wavy ribs (photos 33, 36). About the fact that D. insignis / D. pseudoinsignis has usually 12-13 ribs (Taylor & Zappi 2004, 449-450), we would say that on average it has 12 to 15 (see photos). Furthermore, the picture that illustrates D. pseudoinsignis in Cacti of Eastern Brazil (2004, 416, pl. 73.1) shows a plant with 15 ribs; the same picture shows the taxon in The New Cactus Lexicon (Hunt et al. 2006, Atlas: 290, 290.2). In any case, 12-13 ribs (or even 12-15) cannot be considered a distinctive feature of D. insignis / D. pseudoinsignis; in almost all populations of D. placentiformis the most mature plants carry that number of ribs (see photos of the others population), with the exception of plants found near Bocaiúva, which have a larger number.

Genus

Discocactus

Other species

boliviensis
ferricola
hartmannii
horstii
placentiformis