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A deciduous shrub, of bushy habit, 6 to 12 ft high, more in diameter; the branchlets covered with a white or tawny, loose felt. Leaves lanceolate, 2 to 5 in. long, 3⁄4 to 13⁄4 in. wide; slightly heart-shaped or cut nearly square at the base, tapering thence to the point, coarsely and angularly toothed, covered above, and more so below, with a whitish or tawny down; stalk 1⁄4 to 1 in. long. Flowers fragrant, produced in June or later in a terminal panicle 3 in. high and 2 in. wide, formed of axillary whorls. Corolla lilac-coloured; the tube 1⁄3 in. long, downy outside; the four-lobed limb about as much in diameter, white near the orifice of the tube. Calyx with erect, ovate lobes, woolly like the stem. Bot. Mag., t. 4793.
Native of Afghanistan and the Himalaya, where it is occasionally a small tree; a similar but not identical plant is found in W. China. At Kew, a plant raised from seed sent home by Dr Aitchison from Afghanistan in 1879 proved perfectly hardy and grew there for more than thirty years without protection. This plant no longer exists, but later introductions have proved as hardy. It is seen at its best when grown on a wall, where it will flower continuously from June to the first frosts if pruned back in spring. It was given an Award of Merit in 1961. This species appeared in previous editions as B. paniculata Wall., which is probably not in cultivation.
Dr Leeuwenberg widens the scope of this species to include B. caryopteridifolia, B. sterniana, B. farreri and B. tibetica. The amount of additional variation imparted to B. crispa by these inclusions is slight, but it becomes of wider geographical range, to Yunnan and western China. Horticulturally the sinking of these species does pose problems, since the plants grown under the various names differ in hardiness and mode of flowering (though even a single plant may vary in the latter respect). Most of the plants distributed commercially as B. crispa probably derive from a plant in the Aldenham collection (A.M. 1961); those under the names B. caryopteridifolia and B. sterniana from Forrest seed collections (possibly the same one); those identified as B. tibetica derive from an introduction by Lord Wigram from the Lloyd Botanic Garden, Darjeeling. The Farrer introduction from Kansu (B. farreri) is the most distinct, and the varietal name B. crispa var. farreri (Balf. f. & W.W. Sm.) Hand.-Mazz. is available for it.