Geranium naming does seem to be an absolute minefield. When the RHS did a trial a few years ago they commented that quite a few of the cultivars or "species" submitted were wrongly named.
Will you accept G. malviflorum, John?
Interestingly, though The Plant List does say one or two alleged subspecies of this are in fact synonyms for G. tuberosum (whereas it says that all "malvifoliums" are synonyms for tuberosum), the main practical difference between G. malviflorum and G. tuberosum at least in the wild is that malviflorum flowers are supposed to be purple, as opposed to pink for tuberosum. But evidently most of the plants offered by nurserymen as malviflorum seem to have pink flowers!
