Species (G-O)

Rh. groenlandicum (Oeder) Kron et Judd

sin. Ledum groenlandicum Oeder

Upright shrub 0,7-2 m high; branchlets rusty tomentose.

Leaves aromatic when bruised, narrowly oblong, 2-6 cm long, 0,5-1,5 cm wide, margins very revolute; upper surface dark green with a few loose hairs; underside tomentose and lepidote, with a thick indumentum, upper layer felty, ferrugineous, obscuring the scales, and a lower layer of short white hairs; densely scaly and with reddish glands.

Petiole short, 1-5 mm.

Inflorescence to 5 cm across, many flowers.

Pedicel slender, downy.

Calyx minute.

Corolla white, rotate, 4-8 mm.

Stamens 7-10.

Ovary glandular.

Style glabrous.

Greenland, Canada, Northern USA. 1,000-1,800 m.

Epithet: From Greenland.

Rh. hirsutum L.

Small shrub 0,3-1 m high; branchlets scaly, often bristly.

Leaves obovate, oblong, oblanceolate or oblong-lanceolate; lamina 0,8-2,6 cm long, 0,4-1,3 cm broad; upper surface dark green, shiny; margin crenulate, bristly; underside pale green, laxly scaly, scales 2-4 times their own diameter apart.

Petiole bristly.

Inflorescence 4-12 flowers.

Calyx 2-5 mm long, margin with long hairs.

Corolla tubular with spreading lobes, 1-2 cm long, rose-pink, scarlet or crimson, outside scaly, inside pubescent, margin of the lobes hairy.

Central European Alps, Austrian Alps, NW Yugoslavia.

Epithet: Hairy.

Rh. impeditum Balf. f. et. W.W. Smith

Small very compact, spreading or rounded shrub 10-80 m high; branchlets short, thick, densely scaly.

Leaves elliptic, oblong-oval, oblong or oblong-elliptic; lamina 0,5-1,6 cm long, 3-6 cm broad; upper surface dark green, in both the adult and young leaves, not glaucous, somewhat shiny, scaly; underside densely scaly, scales one-half their own diameter apart.

Inflorescence 1-3 flowers.

Corolla widely funnel-shaped, 0,9-1,6 cm long, pale or deep purple, intense blue-purple, bright violet, lavender or pale or deep rose-purple.

Stamens 10, long-exserted.

Mid-W and NW Yunnan, SW Sichuan. 3,650-4,900 m.

Epithet: Tangled.

Rh. insigne Hemsl. et E.H.Wilson

Shrub 1,6-6 m high; branchlets moderately or densely whitish tomentose, eglandular.

Leaves lanceolate, oblong-lanceolate or oblanceolate; lamina rigid, 6,8-11 cm long, 1,6-5 cm broad, apex acuminate; upper surface dark green, somewhat shiny, glabrous; underside shiny with a thin, plastered, continuous, pale coppery, unistrate indumentum of hairs (in young leaves woolly, white).

Inflorescence in trusses of 6-16 flowers.

Pedicel slender, eglandular.

Corolla campanulate, 2,8-4 cm long, pale or deep pink, red, or white-flushed rose or red down the middle of the lobes, with or without crimson spots.

W Sichuan. 2,150-3,000 m.

Epithet: Remarkable.

Rh. kaempferi Planch.

sin. Rh. obtusum v. kaempferi Wils.

Shrub 30 cm-3 m high; young twigs densely brown-strigose, eglandular.

Leaves evergreen or semi-evergreen, chartaceous, dimorphic; spring leaves lanceolate, elliptic or ovate, 2-5 cm long, 1-2,5 cm broad, mostly deciduous; summer leaves smaller, oblong-obovate, obovate or elliptic, mostly persistent through the winter; in both types, upper surface is glossy green, underside is paler, brown-strigose on both surfaces and on the margin.

Inflorescence 2-4 flowers.

Pedicel densely brown-strigose.

Calyx brown-strigose.

Corolla funnel-shaped, 2,6-3,8 cm long, 2,5-4,3 cm across, salmon-red, brick-red or some shade of red.

Stamens 5.

Japan. Sea-level to about 1,600 m.

Epithet: After E. Kaempfer (1651-1716), who wrote about Japanese plants.

Rh. keleticum Balf. f. et Forrest

sin. Rh. calostrotum ssp. keleticum Balf. f. et Forrest

A very compact, rounded spreading shrub, 15-45 cm high; or a semiprostrate shrub 8-15 cm high; branchlets densely scaly, not bristly.

Leaves oblong, oblong-elliptic, lanceolate; lamina 0,7-2,1 cm long, 3-9 mm broad; upper surface dark green, shiny; underside densely scaly, scales overlapping.

Petiole scaly, not bristly.

Inflorescence 1-3 flowers.

Calyx 5-8 mm long, lobes pinkish or crimson.

Corolla widely funnel-shaped, 1,6-3 cm long, deep purplish-crimson or deep purplish-rose, with crimson spots, outside rather densely pubescent,  scaly along the middle of the lobes.

E and SE Tibet, NW Yunnan. 3,950-4,575 m.

Epithet: Charming.

Rh. kiusianum Makino

Shrub, low dense much-branched, often prostrate, sometimes broadly upright,  0,3-1 m high; young shoots densely brown-strigose.

Leaves evergreen or semi-evergreen, chartaceous, dimorphic; spring leaves broadly, ovate or obovate, small, 0,8-2 cm long, 0,5-1 cm broad; summer leaves smaller, obovate, oblanceolate, elliptic or ovate, the uppermost ones are persistent through the winter; in both types upper surface is glossy, dark green, underside paler, brown-strigose on both surfaces and on the margin.

Inflorescence 2-3 flowers.

Corolla funnel-shaped, small, 1,5-2 cm long, 1,3-2,5 cm across, rose-purple, purple, red or pink, sometimes white.

Stamens 5.

Japan. 600-1,600 m.

Epithet: From Kyusu, Japan.

Rh. kotschyi Simonkai

sin. Rh. myrtifolium Schott et Kotschy

Small shrub 30-45 cm high; branchlets scaly, not bristly.

Leaves oblong, oblong-obovate or oblanceolate; lamina 0,9-2,3 cm, long, 5-8 mm broad; upper surface dark green, shiny, not scaly; margin crenulate; underside densely scaly, scales contiguous or slightly overlapping or one-half their own diameter apart.

Petiole scaly, not bristly.

Inflorescence 3-7 flowers.

Pedicel scaly, rather densely or moderately minutely puberulous.

Corolla tubular, tube slender, with spreading lobes, crimson-purple, scarlet-purple, rosy-purple or rarely white, rather densely pubescent on the tube, moderately pubescent on the lobes.

Transylvanian and Carpathian mountains and the mountains of Bulgaria and Yugoslav Macedonia. 1,500-2,400 m.

Epithet: With myrtle-like foliage.

Rh. ledebourii Pojark.

sin. Rh. dauricum var. sempervirens

Altai Mountains, Russia.

Rh. ledebourii v. album

Rh. ledebourii v. roseum

Rh. luteum Sweet

Shrub 0,6-3,6 m high, stoloniferous; young shoots setulose or not setulose, glandular with long-stalked glands.

Leaves deciduous, oblong, oblong-obovate or oblong-lanceolate; lamina chartaceous, 5-11 cm long, 1,3-4 cm broad, upper surface dark green or pale green, strigose-glandular; margin serrulate, strigose; underside strigose-glandular.

Inflorescence 7-12 flowers.

Corolla tubular-funnel-shaped, 3,2-4,5 cm long, yellow with a darker (yellow) blotch, flowers opening before the leaves, very fragrant.

Pedicel glandular, outside glandular, viscid.

Calyx glandular.

Stamens 5.

Caucasus, N Turkey, SW Russia, Georgia, Ukraine. Sea-level to 2,200 m.

Epithet: Yellow.

Rh. makinoi Tagg ex Nakai

Shrub 1-2,4 m high; branchlets densely brown woolly, eglandular; leaf-bud scales persistent..

Leaves lanceolate or narrowly lanceolate; lamina 5-17 cm long, 0,8-2,5 cm broad; upper surface dark green or bright green, glabrous (in young leaves, whitish woolly); margin recurved; underside covered with a thick, woolly, brown, continuous bistrate indumentum.

Petiole densely brown woolly, eglandular.

Inflorescence a candelabroid umbel of 5-8 flowers.

Calyx 1-7 mm long, densely hairy, eglandular.

Corolla funnel-campanulate, 3-4 cm long, pink or rose, with or without crimson spots.

Central Honshu, Japan. 450-550 m.

Epithet: After T. Makino, a Japanese botanist.

Rh. maximum L.

Shrub 1,2-3,7 m or sometimes a tree up to 12 m high; branchlets floccose, moderately or rather densely glandular.

Leaves lanceolate or oblong-obovate; lamina 9-20 cm long, 2,5-7 cm broad; upper surface dark green, glabrous; underside with a thin film of hairs, or covered with a thin, continuous unistrate indumentum of hairs, or glabrous.

Petiole often glandular.

Inflorescence a candelabroid umbel of 12-30 flowers.

Pedicel rather densely glandular.

Calyx glandular.

Corolla campanulate, 2,3-3,1 cm long, white, pink, rose or purplish, with yellowish-green spots;

Ovary densely glandular.

Style glandular throughout to the tip with white or yellowish glands.

Ontario, Quebec, Nova Scotia southward along the Appalachian Mountains to Georgia. From nearly sea level to about 900 m.

Epithet: Maximum.

Rh. micranthum Turcz.

Shrub 0,6-2,5 m high; branchlets thin, scaly, rather densely minutely puberulous.

Leaves oblanceolate or lanceolate; lamina 1,5-3,8 cm long, 0,4-1,5 cm broad; upper surface dark green, shiny; underside densely scaly, scales overlapping or contiguous or 5 times their own diameter apart.

Petiole scaly, minutely puberulous.

Inflorescence racemose, 10-28 flowers, rhachis 1-2,6 cm long.

Corolla campanulate, small, 4-6 mm long, white, outside scaly.

N and central China, Manchuria, Korea. 1,600-3,000 m.

Epithet: Small flowers.

Rh. molle ssp. japonicum (A.Gray) Kron

sin. Rh. japonicum (A.Gray) Suringar

Shrub 0,6-1,8 m high, occasionally stoloniferous; young shoots setulose, eglandular.

Leaves deciduous, elliptic, obovate, oblong-obovate or oblanceolate; lamina chartaceous, 5-11,5 cm long, 1,8-3,5 cm broad, upper surface dark green, strigose, eglandular, margin strigose; underside pale green, not pubescent, not setulose, strigose only on the lateral veins, midrib strigose.

Petiole setulose.

Inflorescence 6-12 flowers, flowers opening before the leaves.

Pedicel setulose.

Calyx margin densely setulose.

Corolla widely funnel-shaped, 4,8-6,2 cm long, orange, yellow. salmon-red or brick-red, with large orange blotch.

Stamens 5.

Japan. Up to 1,000 m.

Epithet: From Japan.

Rh. molle ssp. molle

sin. Rh. molle (Bl.) G.Don

Shrub 0,3-1,2 m high; young shoots villous, eglandular.

Leaves deciduous, oblong, oblanceolate or oblong-lanceolate; lamina 6-15 cm long, 1,8-5,6 cm broad, upper surface often pubescent, eglandular; margin serrulate, strigose; underside often rather densely pubescent, eglandular.

Petiole often setulose, eglandular.

Inflorescence 6-12 flowers, flowers opening before or with the leaves.

Calyx minutely puberulous.

Corolla widely funnel-shaped, 4,3-5,6 cm long, golden-yellow, yellow or orange, with a large greenish blotch separated into dots.

E China, in Hubei, Zhejiang and Jiangsu.

Epithet: With soft hairs.

Rh. morii Hayata

Mora rododendrs

Rh. mucronulatum Turcz.

sin. Rh. dauricum v. mucronulatum Turcz.

Shrub 1-4 m high; branchlets slender, scaly.

Leaves deciduous, elliptic, elliptic-lanceolate or lanceolate; lamina thin, 3,2-8 cm long, 1,3-3,6 cm broad; upper surface bright green, scaly; margin crenulate; underside pale green, scaly, scales 2-4 times their own diameter apart.

Petiole scaly, not bristly or sometimes bristly.

Inflorescence terminal, or terminal and axillary, 1-3 flowers.

Corolla widely funnel-shaped, 2,3-2,8 mm long, precocious (flowers appearing before the leaves), rose, rose-purple or reddish-purple, outside not scaly, pubescent.

SE Siberia, Manchuria, N China, Korea, Japan.

Epithet: With a small point.

Rh. x 'Obtusum'

sin. Rh. kiusianum x Rh. kaempferi 

Low shrub up to 1 m high, rarely more, sometimes nearly prostrate, twiggy; branchlets densely brown-strigose.

Leaves partly evergreen, dimorphic; spring leaves (which are formed immediately after the flowers open) are deciduous, chartaceous, lanceolate, elliptic-lanceolate to ovate, bright green above, pale beneath, both surfaces strigose; summer leaves evergreen, fairly coriaceous, smaller, obovate or oblong-obovate, both surfaces strigose.

Inflorescence 1-3 flowers.

Pedicel densely strigose.

Calyx 1-3 mm long.

Corolla funnel-shaped, 2,4-2,8 cm long, bright red, scarlet, crimson, salmon or salmon-red.

Japan.

Epithet: Blunt.

Rh. occidentale (Torr. et Gray) A. Gray

Shrub 0,6-4,5 m high; young shoots glabrous or minutely puberulous.

Leaves deciduous, oblanceolate, lanceolate, oblong-lanceolate, obovate or elliptic; lamina 4-9 cm long, 1,5-3 cm broad, upper surface bright green or dark green, often minutely pubescent; margin rather densely strigose; underside often minutely pubescent, midrib strigose.

Inflorescence 5-12 flowers, flowers opening with or after the leaves, fragrant.

Calyx 1-6 mm long.

Corolla tubular-funnel-shaped, 4,2-5 cm long, white, pink, orange-pink, red or yellow, with or without stripes and spots, usually with yellow or orange blotch, outside villous, glandular.

From S Oregon to S California. Sea level up to 2,750 m.

Epithet: Western.

Rh. orbiculare Decne.

Compact rounded shrub or tree 1,5-3 m high or more; branchlets bright green, glaucous, glabrous, eglandular.

Leaves orbicular or ovate-orbicular; lamina 4-10 cm long, 4-8 cm broad, base deeply cordate, auricled, auricles usually overlapping; upper surface bright green, matt, glabrous; underside glaucous, papillate, glabrous, under magnification punctulate with minute glands.

Inflorescence in trusses of 7-16 flowers.

Pedicel often glandular.

Corolla widely campanulate with a broad base, 3,2-4 cm long, rose, rosy-red, deep red or reddish-purple, lobes 7.

Stamens 14.

W Sichuan. Border between Sichuan and Yunnan. 2,300-4,000 m.

Epithet: Circular, alluding to the leaves.

Rh. oreodoxa Franch.

Shrub or small tree 1,5-5 m high; branchlets often with a thin whitish tomentum.

Leaves oblong or oblong-oval; lamina 5-10,5 cm long, 1,8-4 cm broad; upper surface bright green or olive-green, matt, glabrous; underside pale glaucous papillate, glabrous.

Inflorescence in trusses of 5-12 flowers.

Pedicel densely or sparsely glandular.

Calyx minute, 1 mm long, glandular.

Corolla tubular-campanulate, 2,6-4,8 cm long, pale rose or pink or rarely carmine, with or without purple spots; lobes 7-8.

Stamens 14; glabrous or puberulous at the base.

Ovary glabrous, eglandular.

W Sichuan, Hubei, Gansu. 2,300-3,800 m.

Epithet: Glory of the mountains.