You will notice that just a few species left. How does it come that all those species disappear or at least are lumped under other species ?
I think that it is due to the big gap between the point of view of a collector and a purely scientific point of view.
First of all, let's try to understand what is a species.
This is the definition that D. Hunt gives in his New Cactus Lexicon : "A series of similar intergrading and interfertile populations, recognizably distinct from other such series and reproductively isolated from other such series". (1)
There's a population of Sulcos showing black spines on Hill A. On Hill B another population (fertile with the first population) showing yellow spines. The term intergrading means that we will find between those 2 hills sulcos with black spines, sulcos with yellow spines and sulcos with spines of both colors together (and of course fertile with each other).
Ideally there's on Hill A 100 % of Sulcos with black spines ; on Hill B there's 100 % of Sulcos with yellow spines ; and between both Hills there's a progressive variation from black to yellow.
The idea of this definition of "species" is that there must be interfertility between populations and distinct features not limited to one population, but shared by intermediate populations.
David Hunt also says : "For taxonomists, however, the emphasis is on classification. For them the species is a more elastic concept, since it is supposed to take into account the variability within and between populations, a point often neglected by many collector-authors in the past. For the most part, the cultivated specimens derived from their introductions have either been raised from seed, originally collected from just one or a few wild individuals, or else propagated from offsets etc, and in fact "cloned" from one individual specimen or just a few. What we have in our collections are thus "selections" (what one distinguished taxonomist called "flower pot species"), and that they seem more or less constant, invariable or predictable, and distinct, is not very surprising. But it does't mean they are all different species in the sense defined above." (1)
This was the scientific approach.
And what is the idea of species for the collector ?
David Hunt says : "For anyone growing or collecting living plants, the desire for the names to be precise and constant is paramount. In essence, and justifiably, the approach shoud be that of the nursery-man's catalogue - so as to be able to specify exactly the plant one has, or is looking for, or is talking about. For every item that looks different or behaves differently, a different name, and the simpler the better, is what is needed."
"Enthusiasts who have visited the habitats realise that many species are much more variable out there than is apparent from the plants in their collections and that the best way to specify exactly the plant one is talking about is to relate it to its precise source, via an individual locality-name or a collector's field number." (1)
Indeed, if you refer to David Hunt's classification, you'll have to label your R. caracarensis, R. inflexiseta, R.crispata, R. rauschii et R. pulchra with only one name : R. pulchra. Even if this is scientifically uncorrect, I think that using "older names" in a collection can give some order to it (if no real classification) and the field number indicates exactly the plant one is talking about.
(1) D. HUNT, N. TAYLOR & G. CHARLES, The New Cactus Lexicon, DH Books, 2006, p. 4