A deciduous shrub of bushy, rounded habit, a few feet high, the erect, or nearly erect, biennial stems covered with purplish bloom, but with few or no prickles. Leaves simple, three- or five-lobed, or sometimes scarcely lobed at all, heart-shaped at the base, 11⁄2 to 5 in. long, about the same wide, glabrous and green above, white but not downy beneath, margins sharply toothed; leaf-stalk often as long as the blade. Flowers 3⁄4 in. across, produced usually three together; stalks glabrous, 3⁄4 in. long; petals white, oblong, calyx downy within, the triangular lobes shorter than the petals. Fruits orange red, composed of comparatively few large carpels. Bot. Mag., t. 8264.
Native of Japan; introduced by Späth of Berlin, and originally distributed as “R. morifolius”. It is rather pretty in blossom, the flowers being abundant, and the purple-red anthers contrasting well with the white petals.
R. koehneanus is perhaps only varietally distinct from R. incisus Thunb. (1784), for which a possible earlier name is R. microphyllus L.f. (1781). This is a smaller plant than R. koehneanus, with more numerous prickles, leaves to only 2 in. or so long, and mostly solitary flowers. The plant in commerce as R. microphyllus ‘Variegatus’ is probably referable to R. incisus, but its flowers have not been seen and indeed it may be sterile. The young leaves are red, becoming green with irregular patches of white suffused pink. It is a rather weak grower, its slender stems covered with a whitish bloom and armed with numerous small prickles.