Rhamnus purshiana DC.

A deciduous tree up to 40 or 50 ft high in the wild; young shoots conspicuously downy. Leaves oblong or oval, rounded at the base, with a short, bluntish apex, either minutely toothed or entire, 2 to 5 in. long, 1 to 3 in. wide, downy beneath and on the veins above, veins parallel, in ten to fifteen pairs; stalk 1⁄2 to 3⁄4 in. long, downy. Flowers in stalked umbels, opening in July; sepals and petals five, flower-stalks downy. Fruits top-shaped, 1⁄3 in. long, black, usually three-seeded.

Native of western N. America; introduced in 1891. A handsome small tree, although without any beauty of blossom, forming a broad leafy head of erect or spreading branches. It is allied to R. frangula, but has more numerous parallel veins in each leaf that are downy above, and differs in the distinctly stalked flower-clusters, the common-stalk being often 1⁄2 in. or more long. R. purshiana is the source of the well-known drug, cascara sagrada, one of the most popular of aperient medicines. It is obtained from the bark, and so great was the demand that £20,000 worth was sent from the states of Oregon and Washington in 1907. The consequence is that natural supplies are being rapidly used up, and it has been suggested that the cultivation of this tree in the southern and western parts of the British Isles might prove profitable. The bark of trees raised and grown at Kew has been proved to possess the aperient quality as fully as that of wild trees.