Ralph,

Selenicereus is for the lumplers, Cryptocereus is for the splitters.

From Cactus-art.biz:

' The Taxonomists are biologists who determine the scientific names of organisms and then group organisms into a hierarchy into an orderly system. In taxonomy There are two tendency about how to classify living things: by their differences or by their similarities. Depending on their personal approach to recognizing differences or commonalities between organisms.

A "lumper" is a taxonomist who group by similar traits, assuming that differences are not as important as similarities. And place organisms which share a few major characteristics in the same group. When two named species are discovered to be of the same species, the older species name is usually retained, and the newer species name dropped, a process called synonymization or convivially, as lumping.
A "splitter" is a taxonomist who takes precise definitions, and creates new categories to classify organism on the basis of the smallest known difference, so every small difference is considered sufficient to create a new separate group. Dividing a taxon into multiple, often new, taxa is called splitting.

For example in the family Cactaceae "lumpers" recognize 30-50 genera and about 1000 species, "splitters" judge right to consider 200 genera and over of 2000 species.

In practice what happens is that organism are grouped on the basis of compromise by the splitters and lumpers.'

Ahso...gracias.