the *genus* Sarracenia has 9 species within it..
each of the species are close enough related to belong to the same genus..
But in the case of the genus Dionaea and Darlingtonia, there just isnt that kind of variety..
one genus, with only species within it.
its just a quirk of nature..perhaps there were once more closely related species, that today might have been classified in the same genus..and perhaps there will be again in the future..
but not at this point in time!