Some of them actually do. In some cases (when morphology fails)
"species" are defined by the type of soil they were found to grow in.
I'm very careful with such differentiation because frequently small
patches of humous (acidic) soil accumulate in places which are otherwise
dominated by calcareous (basic) earth. And one can never exclude the
factors affecting the (present) distribution of certain taxa to be other
than geologic.
As many cps have a reduced root system (i.e. reduced mineral uptake), it
may even be certain plant communities (which in turn may be affected by the
soil) rather than specific properties of the substrate which are preferred
by the cps.
Clearly "calciphilous" elements of the European _Pinguicula_ flora are
_P.longifolia_ (all sspp.) and _P.vallisneriifolia_, growing
exclusively on north facing wet limestone rocks, but the other spp. may
tolerate calcareous soils to a certain degree as well.
Kind regards
Jan