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A shrub varying considerably in height, at its tallest 12 to 15 ft high, more often 6 to 8 ft high, the main stems erect, but producing towards the top slender, arching or pendulous branches growing 3 ft or more long in one season; the young branches ribbed and downy. Leaves 1⁄2 to 1 in. long, 1⁄3 to 5⁄8 in. wide, oval or obovate, usually blunt and toothed at the apex, and always more or less tapering to the very short stalk at the base, dull green and with some down above, grey and more or less thickly downy beneath. Flowers white, or dull creamy white, small, produced during June and July in corymbs 1 to 2 in. across, at the end of short leafy twigs; flower-stalks and calyx grey-downy or even felted.
Native of the Himalaya; introduced in 1837. The chief distinguishing characteristic of this spiraea, and one which gives it a leading place in the genus, is its habit of producing in one season the long, thong-like shoots to which the former popular name “flagelliformis” refers. When, the following year, there springs from every bud a short erect twig, each crowned with its dense cluster of flowers, there are few more strikingly beautiful shrubs, especially at the date when it blossoms. The species is somewhat variable in the shape and size of the leaf, in the amount of down it bears, also to some extent in habit. It has, in consequence, received many names. The small greyish leaves tapering at the base, and the abundant clusters of white flowers set on the upper side of long arching branches, generally distinguish it.
The above account of S. canescens is taken from previous editions. This species has now been largely displaced in gardens by its Chinese allies, notably S. veitchii.