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A deciduous shrub or small tree, with glabrous, slightly zigzag, ultimately dark brown branchlets. Leaves oval or ovate, long-pointed, sharply saw-toothed, 21⁄2 to 3 in. long, about 1 to 11⁄2 in. wide, glabrous and glossy green at maturity; leaf-stalk 1⁄2 to 3⁄4 in. long with a pair of glands towards the top, remaining downy longer than the blade. Flowers white, 5⁄8 in. across, produced during the second week of May in clusters of three or four; petals narrowly obovate; calyx-lobes downy on the inner surface and margins, not toothed; flower-stalk 1⁄3 in. long, glabrous. Fruits round, 1 in. across, nearly black covered with a blue bloom; flesh juicy, palatable.
This plum was described by Koehne in 1893 from a plant growing in Späth’s nursery, Berlin, to which it had been introduced from the Arnold Arboretum. The original seeds were received by that institution in 1880 and according to the records were collected by Dr Engelmann in Texas. It has not been found wild there, and there is some evidence that the seeds really came from Kansas, where similar plants are found wild. These, and the typical P. orthosepala, may be hybrids between P. americana and P. watsoniana. The orchard variety ‘Laire’, cultivated in Kansas, is near to P. orthosepala.
This plum was at one time represented at Kew by a small tree obtained from Späth’s nurseries in 1896.