Cultivar classification of Philadelphus L. (Hydrangeaceae)

The cultivars of the genus Philadelphus are up till now usually classified in five interspecific hybrids, as proposed by A. Rehder some 70 years ago. This system is not satisfactory any more. Instead a new, more stable classification of four cultivar groups is proposed here. This new classification shows influences of Rehder’s system, but differs quite a lot in its principles. The new classification is based on practical application (culton concept), while the old classification is based on genetic relationships (taxon concept). The definitions of the cultivar groups are simple and clear, cultivars can be classified better and this system is easy to work with, even for non-specialists. The proposed cultivar groups are: Lemoinei group, Purpureo-maculatus Group, Virginalis Group and Burfordensis Group.