Low shrub, 0.3-1 m; young shoots covered with greyish spreading-pilose, sometimes gland-tipped, hairs, also with a few bristles. Leaves of two kinds; spring leaves deciduous, 2.5-7 x 1.5-2.5 cm, ovate-elliptic, apex acute, lower surface with gland-tipped hairs, with a few bristles on the midrib and main veins; summer leaves persistent, 1.2-2 x 0.3-0.6 cm; petioles densely pilose, also with a few flattened setae. Pedicels covered with long spreading pilose, partly gland-tipped hairs. Flowers 2-10 per inflorescence; calyx 15-30 mm, lobes lanceolate to broadly oblong; corolla lilac-pink to rose-purple, with purple flecks on upper lobe, broadly funnel-shaped, 35-50 mm; stamens 5(-7); ovary covered with gland-tipped bristles, style glabrous. Flowering May-June. Royal Horticultural Society (1997)
Distribution Japan Honshu, Shikoku
Habitat 150-400 m
RHS Hardiness Rating H4
Awards AM 1984 (E. de Rothschild, Exbury) as R. macrosepalum 'Linearifolium'; trusses 3-5-flowered, corolla divided almost to base, with segments widely deflexed, red-purple with some darker marking.
Conservation status Least concern (LC)
Taxonomic note (incl. R. macrosepalum Maxim.) Royal Horticultural Society (1997)
This species is closely allied to R. ripense (q.v.). It may hybridize with R. kaempferi in the wild. R. linearifolium Sieb. & Zucc., which is equivalent to the type of R. stenopetalum, is an aberrant plant with very narrow leaves and linear corolla lobes that is only known in cultivation. Plants from the wild correspond to R. macrosepalum and conform to the description given above. Royal Botanic Gardens, Kew (2019)