Philadelphus subcanus Koehne

This species is very closely allied to P. incanus and was first separated from it in 1904. It differs in having the calyx and the underside of the leaves more sparsely hairy; also the disk and the lower part of the style are downy (glabrous in P. incanus). Native of W. Szechwan. Wilson may have introduced it while collecting for Messrs Veitch, but it is mainly and perhaps wholly represented in cultivation by Wilson’s introduction during his first expedition for the Arnold Arboretum. The plants (sometimes labelled P. wilsonii) flower earlier than P. incanus, in late June or early July.At Wakehurst Place in Sussex there are plants of unknown origin, the largest 15 ft high and as much wide, which agree with P. subcanus except that the style and disk is glabrous, as in P. incanus. The best is very free flowering, with racemes of up to eleven flowers, usually the lower two pairs in the axils of normal leaves.

From the Supplement (Vol V):

Plants at Wakehurst Place, Sussex, grown under Philadelphus subcanus differ from the species as defined by Hu in having the style and disk glabrous. It is interesting that plants raised from Lancaster 498 and 524, collected in western Szechwan on Mount Omei in 1980, also differ from P. subcanus in this respect and would actually run down to P. sericanthus in Hu’s key to the series Sericanthi (Journ. Arn. Arb., Vol. 36, p. 337). However, they disagree in other respects, and there is the further consideration that P. sericanthus has not been reported from western Szechwan, while several specimens collected on Mount Omei are referred by Hu to P. subcanus. Plants from the new introduction grow vigorously and first bore flowers in 1985. They have a strong, distinct fragrance.