Philadelphus Linnaeus. Mock-orange.
A genus of 65 (or fewer) species, shrubs, of north temperate areas. The most recent monographer of the genus, Hu (1954-1955) recognizes many species and varieties on the basis of minor differences in pubescence. Many of the recognized taxa are based only on cultivated material. The native distributions of the varieties have little phytogeographic coherence, and several varieties are often reported from the same site, suggesting that they reflect merely variation within a population (if genetically based at all). For instance, Hu recognizes three varieties in P. hirsutus and five in P. inodorus, but these seem to be no more than forms. As Hu writes, "the formerly recognized species, P. grandiflorus Willd., and P. laxus Schrad., are merely different forms of a species with heterogeneous leaf shape, size, and margins. Fostered by growers, propagated and distributed through cuttings, these forms have maintained their distinction in gardens since their discoveries. But when they are projected on the spectrum of variations exhibited by a large number of specimens collected from the homeland of P. inodorus Linn. they appear to be nothing but a few transitional forms. In this paper, these forms are treated as varieties." Hu's "varieties" should be treated as forms or cultivars, if recognized at all. I have taken a conservative approach, though variation in several of our native species could use additional study.
Ref: Hu (1954-1956); Hufford (2004) In Kubitzki et al. (2004); Weakley (2002); Weakley & Henrickson (2016) In Flora of North America Editorial Committee (2016). Show full citations.