Pocket Guide to Rhododendron Species - Royal Botanic Gardens ...

470 Pocket guide to Rhododendrons
R. sulfureum Franch. Boothia Gp B
Shrub often epiphytic, 0.3–1.5 m (1–5 ft) high; branchlets scaly.
Leaves obovate, oblong-obovate, elliptic or oval; lamina 2.6–8.6 cm long,
1.3–4.2 cm broad; upper surface bright or dark green; underside glaucous,
densely scaly, scales one-half to their own diameter apart.
Inflorescence 4–8 flowers.
Calyx 3–6 mm long.
Corolla campanulate, 1.3–2 cm long, bright or deep yellow, bright or deep
sulphur-yellow, or greenish-yellow, outside scaly.
Style short, stout and sharply bent.
W and NW Yunnan, NE Upper Burma. 2,150–3,850 m (7,000–12,620 ft).
AM 1937 (Lochinch), as R. commodum, flowers sulphur-yellow.
Epithet: Sulphur-coloured. Hardiness 2–3. March–April.
Large calyx but small flowers.
Subgenus Rhododendron
Section Rhododendron
Subsection Camelliiflora
Camelliiflorum Series
R. camelliiflorum Hook.f.
Shrub 0.6–1.8 m (2–6 ft) high; branchlets rather densely scaly.
Leaves oblong, oblong-lanceolate or oblong-elliptic; lamina 4.8–12.3 cm long,
1.5–3.8 cm broad; upper surface dark green, not scaly; underside densely scaly,
scales contiguous or slightly overlapping or one-half their own diameter apart.
Petiole densely scaly.
Inflorescence terminal, 1–2 flowers.
Pedicel densely scaly.
Calyx 0.5–1.1 cm long.
Corolla campanulate with 5 spreading lobes, 1.5–2.5 cm long, white, white
tinged pink, red or deep wine-red; outside scaly.
Stamens 12–16.
Style short, stout and sharply bent.
Sikkim, Nepal, Bhutan. 2,750–3,650 m (9,000–12,000 ft).
Epithet: With Camellia-like flowers. Hardiness 1–2. May–July.
Rare in cultivation. Flowers often hidden beneath the leaves.
Very variable in
growth habit, but
often straggly.
Leaves obovate,
oblong-obovate,
elliptic or oval.
Leaf underside with
small, brown or dark
brown, scales with
up-turned rims.
Calyx (3–6 mm) and
corolla (1.3–2 cm),
smaller than those
of R. dekatanum.
Leaf underside glaucous.
Inflorescence 4–8
flowers.
Corolla shades of
yellow.
The small flowers
are reminiscent of
Subsection Boothia.
Leaves and growth
habit similar to
those of Subsection
Maddenia.
Distinguished from
most Maddenia
species by the
intensely lepidote
leaves.
Corolla with 5
spreading oval lobes.
Style short, stout
and sharply bent.
Leaf underside with
scales contiguous or
slightly overlapping.
Pedicel densely scaly.
Inflorescence 1–2
flowers.
Corolla white, or pink to
deep wine red.
R. sulfureum F24235 at Brodick Castle
R. camelliiflorum S&L5696 at Benmore
Rhododendron
(Boothia Group B/Camelliiflora)