Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Philadelphus schrenkii' from the website Trees and Shrubs Online (treesandshrubsonline.
A vigorous deciduous shrub up to 12 ft high; young shoots brown, slightly hairy; bark peeling the second year. Leaves ovate, sparsely toothed, slender-pointed; 11⁄2 to 41⁄2 in. long and about half as much wide on the virgin shoots, smaller on the flowering ones; slightly downy beneath, less so above. Flowers about 11⁄2 in. wide, in five- or seven-flowered racemes; style usually hairy at the base; calyx-tube and flower-stalks hairy.
Native of the Amur region, Korea, and N. China; introduced in 1874. This vigorous shrub is one of the earlier flowering species of philadelphus. A fine bush 12 ft high in Col. Stern’s garden, near Worthing, flowers in late May and early June. In the summer of 1930 I noticed the ground beneath it was freely sprinkled with seedlings that had sprouted from the seeds of 1929. It is quite an ordinary philadelphus, with no strongly marked qualities or characteristics; but the racemose inflorescence, the peeling bark of the year-old shoots, and the style being hairy at the base are the more distinctive ones.
The plant in the garden of the late Sir Frederick Stern, mentioned above, was raised from seeds collected by Reginald Farrer in Kansu.