The current trend among professional botanists is to lump things, as Jim said. Nevertheless the population genetics literature often reveals considerable genetic differentiation between subpopulations of conspecific plants. Current trends in conservation genetics favor the preservation of such genetic variation, in order to ensure the long-term viability of the species.
Giving each form a name at a subpecific level is the first step to preserving this kind of intra-specific variation in nature or ex situ. It may strike modern botanists as old-fashioned to give names to every little variation (and indeed this process often can go overboard), but it does little harm, and is quite helpful in conserving the diversity of a population.
Lou Jost