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

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36 Pocket guide to Rhododendrons R. arboreum ssp. zeylanicum (Booth) Tagg R. zeylanicum Booth Shrub or tree 1.8–11 m (6–35 ft) high or more, branchlets moderately or densely tomentose, glandular. Leaves ovate, ovate-elliptic, elliptic or oblong-elliptic; lamina coriaceous, 5.6–17.5 cm long, 2.5–8 cm broad; upper surface dark green, convex, markedly bullate, glabrous; margin recurved; underside matt or shiny, with a thick somewhat woolly or thin-plastered, continuous, bistrate indumentum of hairs, midrib often glandular. Primary veins often sparsely glandular. Petiole tomentose, glandular. Inflorescence very compact trusses of 12–20 flowers. Pedicel tomentose, glandular. Corolla tubular-campanulate, 3.2–4.1 cm long, crimson or pink, 5 nectar pouches. Sri Lanka, Manipur, Assam. 900–2,750 m (3,000–9,000 ft). Epithet: From Ceylon. Hardiness 1–3. June–July. Recent observations by S. Hootman indicate that R. arboreum ssp. zeylanicum is variable in the wild, extreme forms having flatter leaves or a whitish indumentum. A recent introduction by T. Hudson is much earlier (April) flowering. The two relict populations of R. nilagiricum and R. zeylanicum are properly distinguished by R. zeylanicum being a glandular expression of R. nilagiricum. R. lanigerum Tagg Shrub or tree 2.4–6 m (8–20 ft) high, branchlets densely fawn or whitish tomentose, eglandular. Leaves oblong, oblong-lanceolate or oblanceolate; lamina 10–25 cm long, 3–7.5 cm broad; upper surface dark green, glabrous (in young leaves densely tomentose with a thick creamy or creamy-white tomentum); underside with a thick woolly, continuous, bistrate indumentum of brown or fawn hairs. Petiole densely or moderately tomentose. Inflorescence in very compact trusses of 16–35 or sometimes up to 50 flowers; flower-bud ovate or nearly orbicular, large, 3–3.4 cm long, densely tomentose. Corolla tubular-campanulate, 3–5 cm long, rose-purple, 5 nectar pouches. Assam. 3,000–3,350 m (10,000–11,000 ft). AM 1949 (Trengwainton), AM 1961 (Stonehurst) ‘Stonehurst’, AM 1961 and FCC 1967 (Windsor) ‘Chapel Wood’. Epithet: Woolly. Hardiness 3. February–April. The red and crimson forms were known as R. lanigerum var. silvaticum but are now regarded as insufficiently distinct to merit varietal status: AM 1951 (Tower Court) as R. silvaticum (KW6258), AM 1951 (Windsor) as R. silvaticum ‘Round Wood’ (KW6258), AM 1954 (Logan) as R. silvaticum ‘Silvia’. Epithet: Woodland. Hardiness 3. February–April. This species and R. niveum are very similar in leaf and indumentum. They may be distinguished by R. niveum’s near-rounded apex, which contrasts with R. lanigerum’s acute/acuminate apex. The leaves of R. lanigerum are usually larger than those of R. niveum. Branchlets moderately or densely tomentose, glandular. Leaf upper surface convex, markedly bullate. Leaf margin recurved; underside with a thick somewhat woolly or thin-plastered, continuous, bistrate coppery indumentum. Petiole tomentose, glandular. Pedicel glandular. Indumentum, though bistrate, can have a shiny plastered coppery appearance. Corolla usually crimson. Indumentum thick woolly, bistrate, brown or fawn. Flower-bud ovate or nearly orbicular, large, densely tomentose. Corolla pink, rose purple, cherry red, scarlet or crimson. Leaf upper surface in young leaves densely tomentose with a thick creamy or creamy-white tomentum. Inflorescence in very compact trusses of 16–35. R. arboreum ssp. zeylanicum – the T. Hudson introduction — at Botallick, Cornwall (M.L.A. Robinson) R. arboreum ssp. zeylanicum – the T. Hudson introduction — at Botallick, Cornwall (M.L.A. Robinson) R. lanigerum at Inverewe Foliage of R. arboreum ssp. zeylanicum – the T. Hudson introduction — at Botallick, Cornwall Ponticum (Arborea)
232 Pocket guide to Rhododendrons R. sperabiloides Tagg & Forrest Neriiflorum Group Shrub 0.6–1.2 m (2–4 ft) high; branchlets with a whitish tomentum, eglandular. Leaves oblanceolate, lanceolate or oblong-elliptic; lamina 3–7.7 cm long, 1.4–2.6 cm broad; upper surface green, glabrous; underside with a thin, interrupted, whitish or fawn, unistrate indumentum of hairs, covered with waxy papillae. Inflorescence in trusses of 4–11 flowers. Pedicel floccose, eglandular. Corolla tubular-campanulate, 2.5–3.8 cm long, deep to light crimson; 5 nectar pouches. E and SE Tibet. 3,700–4,000 m (12,000–13,000 ft). AM 1933 (Exbury), flowers deep crimson. Epithet: Like R. sperabile. Hardiness 3. April–May. Plants cultivated as R. albertsenianum may often be found to have the waxy papillae, giving a pale appearance to the leaf surface under the indumentum, and are therefore referable to this species. Subgenus Hymenanthes Section Ponticum G.Don Subsection Neriiflora Sleumer Sanguineum Group Ovary impressed, i.e. not tapered into the style. All species have thinner indumentum than in Haematodes Group. Further grouping within Sanguineum may be helpful:- Sanguineum Group (Part A). Moderately thick indumentum, but leaf veins visible. Sanguineum Group (Part B). Indumentum appears continuous and is adpressed and whitish or fawn. Sanguineum Group (Part C). Leaves glabrous or almost glabrous. Leaf shape like R. sperabile. The lower leaf surface is glaucous and waxy under the partial indumentum, which is thick, interrupted, whitish or fawn. Corolla deep to light crimson. R. sperabiloides at Deer Dell. This species is often wrongly labelled R. albertsenianum Leaves of the Sanguineum Group of Subsect. Neriiflora at Deer Dell. Top to bottom (all 2 leaves each): left, R. dichroanthum ssp. septentrionale, R. temenium var. temenium and R. eudoxum var. eudoxum; middle, R. dichroanthum ssp. dichroanthum, R. aperantum and R. dichroanthum ssp. apodectum; right, R. citriniflorum var. citriniflorum, R. parmulatum and R. sanguineum ssp. didymum. Bar = 5 cm Ponticum (Neriiflora/Sanguineum Group)
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