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A shrub to about 15 ft high, rarely a small tree; young stems glabrous, purplish by winter and coated with a ‘whitish bloom; winter-buds large, roundish, glabrous. Leaves 21⁄2 to 4 in. long, oblong or narrowly lanceolate, acuminate, glabrous, bright green above, glaucous beneath, remotely toothed or entire; petiole 1⁄8 to 3⁄8 in. long. Catkins dense, almost sessile, appearing before the leaves, 1 in. or slightly more long; scales dark at the tips, obtuse, densely hairy. Stamens with glabrous filaments and reddish anthers. Ovary glabrous, very shortly stalked; style short, with stout, entire or bifid stigmas.
Native of the south-western USA (Colorado, S.E. Arizona and western New Mexico), common along mountain streams; introduced to Kew from the Arnold Arboretum in 1910 (a male clone). With its bloomy stems it is ornamental in winter, though no more so than S. daphnoides, from which it differs in its almost entire, very shortly stalked leaves and smaller catkins. Once established it should be pruned hard each spring. Award of Merit 1967. The specific epithet means ‘dewy’, in allusion to the pruinose stems.
S. lasiolepis Benth. – Closely allied to S. irrorata and described one year earlier. The main difference appears to be that the mature stems are not bloomy (except in some areas where the species overlap) and that they and the leaves are usually downy when young. Its catkins are somewhat longer.
The affinity of these two species is uncertain and controversial. At any rate, S. irrorata, despite its bloomy stems, is in no way related to S. daphnoides. Even in winter it is distinguished by its appressed, beetle-shaped buds, very different from the diverging buds of S. daphnoides and its allies.