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Deciduous shrub or small tree, to 4(-8) m; vegetative shoots arising from buds in the axils of the previous year’s leaves; young twigs glabrous or sparsely covered with eglandular and gland-tipped hairs. Leaves turning red in autumn, arranged in pseudowhorls of 5(-7) at the apices of the branches, 2.1-6.3 x 1.1-3.8 cm, elliptic to obovate, apex acuminate to acute, base cuneate, lower surface glabrous to very sparsely unicellular-pubescent towards base, veins and midrib sometimes covered with straight or crisped eglandular or glandular hairs. Pedicels glabrous or covered with gland-tipped hairs. Flowers fragrant, appearing before or with the leaves, 1-2, in a contracted raceme; calyx 0.5-5 mm; corolla pink to deep rose, usually with red-brown flecks on upper three lobes, rotate-campanulate, the short tube gradually expanding into the longer limb, 15-35 mm. Capsule glabrous. Flowering March-April. Royal Horticultural Society (1997)
Distribution Japan Honshu, Shikoku, Kyushu
Habitat 500-1,700 m
RHS Hardiness Rating H4
Awards AM 1942 (Lord Aberconway, Bodnant); flowers Rose Bengal, paler with age.
Conservation status Least concern (LC)
Taxonomic note This species is most closely allied to R. quinquefolium (q.v.).Royal Horticultural Society (1997)
A deciduous, sometimes tree-like azalea up to 20 ft high; young shoots often in tiers, thinly hairy when young, red-brown, becoming grey the second season. Leaves produced in a whorl of five at the end of the shoot, oval to oval-lanceolate, pointed, wedge-shaped at the base, 11⁄4 to 21⁄2 in. long, half as much wide, midrib downy on both surfaces, margins toothed and ciliate; stalk 1⁄8 to 1⁄3 in. long, thinly glandular-hairy. Flowers terminal, opening in April or May, solitary or in pairs; flower-stalk 1⁄2 in. long, varying from densely glandular to quite glabrous. Calyx with five triangular teeth 1⁄5 in. or less long. Corolla bright rose-pink, not spotted, 2 in. wide, with five spreading, rounded, often notched lobes. Stamens ten, of unequal length, downy at the base; anthers yellow; ovary and style glabrous. (s. Azalea ss. Canadense)
Native of central and southern Japan, where it grows in woodland, and is fond of partial shade. Wilson, who saw it wild in the Nikko region, wrote highly of its beauty both in bloom and in autumn, when the leaves change to rich orange and crimson.
In its foliage it resembles R. quinquefolium, but that species has white flowers, and produces its flowers and leafy shoots from the same bud, whereas in R. pentaphyllum they come from separate buds. It is rather slow to flower and prefers a sheltered place in moist leafy soil.
R. pentaphyllum received an Award of Merit on April 14, 1942, when shown by Lord Aberconway, Bodnant.