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Shrub, to 3 m; young shoots more or less glandular, later glabrescent. Leaves in whorls of up to three, at the ends of the branches, 2.5-6 x 1.5-5 cm, broadly rhombic-ovate, apex shortly cuspidate, lower surface pale, with adpressed hairs or glabrous except for minute papillate glands and long hairs on midrib; petioles glandular. Pedicels glandular, pilose below. Flowers 1-3 per inflorescence, appearing with the leaves; calyx c.3 mm, lobes purple, ribbon-like; corolla magenta, funnel-campanulate, 25-30 mm; stamens 10; ovary shortly stalked-glandular, with scattered pilose hairs, style glabrous. Flowering April-May. Royal Horticultural Society (1997)
Distribution Japan S Hokkaido, mountains.
Habitat c.175 m
RHS Hardiness Rating H6
Conservation status Least concern (LC)
This species is probably allied to R. decandrum but it is distinguished from it and all the remaining members of the section by the conspicuous calyx. It is isolated from the related species and has a very restricted distribution. Royal Horticultural Society (1997)