Author

GP Jürgens

Ericaceae

Rhododendron nivale

by GP Jürgens

Hook. f.

BhutanPG2011 525
Bhutan Ludlow-Sherriff-Trail Dem-Tso, 4650m June

Description

Rhododendron nivale is a dwarf, high-alpine rhododendron of the eastern Himalaya and Tibetan ranges, occurring in southern China (notably Xizang), Nepal, northern India, Bhutan and northern Myanmar, with around 1285 GBIF records. As its epithet ("of the snows") implies, it is one of the highest-ascending woody plants in the world, forming low, wind-pruned cushions and mats on open alpine slopes, moraine, rocky turf and near the snowline. The Bhutanese population imaged on the Ludlow-Sherriff Trail at Dem-Tso at 4650 m in June exemplifies its extreme elevational habitat and its early-summer flowering as the snow recedes.

It is a much-branched, prostrate to low-growing evergreen shrublet with twigs densely set with overlapping scales (lepidote). The leaves are very small, elliptic to obovate, leathery, and conspicuously scaly on both surfaces, the lower side often rusty with dense scales. The flowers are borne singly or few together at the branch tips; the corolla is small, broadly funnelform to rotate, and pink, rose-purple to bluish-purple, with the tube hairy within and exserted stamens. The fruit is a small, scaly, dehiscent capsule releasing minute seeds adapted to wind dispersal in the open high mountains.

Rhododendron nivale belongs to subsect. Lapponica (sect. Rhododendron), the lepidote alpine "dwarf" rhododendrons that dominate vast areas of Sino-Himalayan alpine scrub, and several subspecies have been recognised across its range. Its cushion habit, dense leaf scaling and reduced stature are classic adaptations to cold, desiccating, high-irradiation subnival conditions. The species is abundant within its zone and not of conservation concern, but as a snowline specialist it is a sensitive indicator of alpine climatic change.

Author: Hook. f. · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, The Plant Hunters' Rhododendrons of the Himalaya, Cullen's revision of Rhododendron subsect. Lapponica (monograph)

Ericaceae

Rhododendron niveum

by GP Jürgens

Hook. f.

Sikkim2003 473 P655
Sikkim Lachung Valley 3100m August
Sikkim2004 409 P699
Sikkim Lachung Valley 3500m May
Sikkim2004 407 P697
Sikkim Lachung Valley 350

Description

Rhododendron niveum is a narrowly distributed eastern Himalayan species native to the Sikkim region of India, with extensions into adjacent China and Bhutan; its 92 georeferenced records, supplemented by occurrences in cultivation in Britain, Sweden, North America and Canada, reflect both a restricted wild range and its prominence in horticulture. It is a shrub or small tree of subalpine forest, rhododendron thickets and open hillsides near the treeline. The populations documented in the Lachung Valley of northern Sikkim between about 3100 and 3500 m, flowering in May and persisting in August, exemplify its high-montane habitat on cool, moist, acidic slopes.

The plant forms a compact tree or large shrub with stout branches. The leaves are obovate-elliptic, leathery and dark green above, their lower surface coated with a dense, persistent, silvery-white to fawn indumentum, the snowy tomentum that gives the species its epithet niveum. The flowers are grouped in dense, rounded terminal trusses; the campanulate corolla is a distinctive smoky lilac to deep purplish-mauve, a colour unusual among Himalayan rhododendrons, with ten stamens and a smooth, elongate ovary. The fruit is a woody, septicidal capsule releasing numerous minute seeds.

Within the vast genus Rhododendron, R. niveum belongs to subsection Arborea and is prized horticulturally for its striking flower colour and felted foliage, having been introduced by J. D. Hooker. Its restricted distribution and dependence on a narrow subalpine belt render it locally vulnerable to habitat loss, grazing and climatic shifts at the treeline, and it is of conservation interest as an eastern Himalayan near-endemic.

Author: Hook. f. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, The Rhododendron Handbook (RHS), Cox & Cox's The Encyclopedia of Rhododendron Species

Ericaceae

Rhododendron papillatum

by GP Jürgens

Balf. f. & R.E. Cooper

Bh09 75 P128
Bhutan Jangchulakha, 3700m June

Description

Rhododendron papillatum is a narrowly distributed eastern Himalayan shrub recorded from Bhutan, China, India and Nepal, and is among the rarer species treated here with only about 19 GBIF occurrences. It grows in the upper temperate to subalpine zone, inhabiting open conifer and mixed forest, rhododendron thickets and shrubby slopes generally between roughly 3000 and 4000 m. The photograph from Jangchulakha in Bhutan at 3700 m in June captures it at its early-summer flowering season, when these high ridges carry a dense understorey of evergreen rhododendrons emerging from winter snow.

It is an evergreen shrub or small tree with stout branchlets. The leaves are leathery and elliptic to obovate, dark green and glabrous above, and distinctively papillate beneath, the lower surface bearing a thin papillose covering (the feature giving the epithet) rather than the dense indumentum seen in many relatives. The flowers are borne in a terminal truss; the corolla is broadly campanulate, white flushed pink to pale rose and usually marked with darker spots within, with numerous stamens and a glandular ovary. The fruit is a woody septicidal capsule that splits to release abundant minute seeds.

Within Rhododendron, this species is placed in subgenus Hymenanthes (the elepidote rhododendrons), a group strongly radiated across the Sino-Himalayan ranges where allopatry and elevation partitioning have produced many local endemics. Its restricted range and modest occurrence count make it a species of biogeographic interest and potential conservation concern, dependent on intact high-altitude forest. Pollination is chiefly by bees and other insects attracted to the conspicuous corollas.

Author: Balf. f. & R.E. Cooper · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, The Genus Rhododendron (Edinburgh / Cullen & Chamberlain)

Ericaceae

Rhododendron pendulum

by GP Jürgens

Hook. f.

Bhutan2014 338
Bhutan Tumching-La 3000m, May
Bh2008 236 P373
Bhutan Tumching-La, 3500m April

Description

Rhododendron pendulum is an epiphytic or epilithic dwarf shrub of the humid Eastern Himalaya, with verified occurrences in China, India, Bhutan and Nepal (further GBIF records from Britain and the United States represent cultivated stock). It is most characteristic of cool, mist-laden temperate forest, where it perches on mossy trunks, branches and rock faces, generally between about 2700 and 3700 m. The Bhutanese material illustrated, from the Tumching-La between roughly 3000 and 3500 m in April and May, captures the species in flower at the close of the cold season in its typical cloud-forest setting.

It is a small, straggling shrub with thin, often pendulous branches densely clothed, like the young growth and leaf undersides, in a soft rusty-brown woolly indumentum. The small, elliptic to oblong leaves are leathery, with revolute margins, dark green and somewhat rugose above and thickly tawny-tomentose beneath. The flowers are borne few together at the branch tips; the corolla is broadly campanulate to rotate, white sometimes flushed pink, and comparatively large for so diminutive a plant. The fruit is a small ovoid capsule that splits septicidally to shed numerous minute seeds adapted to dispersal in the canopy.

Rhododendron pendulum belongs to subgenus Rhododendron, section Pogonanthum and its allies, distinguished by its woolly indumentum and epiphytic habit, and was described by J.D. Hooker from his Sikkim explorations. Its dependence on permanently humid, moss-rich forest makes it a sensitive indicator of intact cloud-forest conditions, and although not presently regarded as threatened, it is vulnerable to forest degradation and to disruption of the orographic mist regime on which its epiphytic lifestyle depends.

Author: Hook. f. · Sources: POWO (Kew), GBIF, Flora of Bhutan, The Genus Rhododendron (Royal Botanic Garden Edinburgh), Flora of China

Ericaceae

Rhododendron poluninii

by GP Jürgens

Davidian

Bh2008 230 G365
Bhutan Tumching-La, 3400m April
Bh2008 231 P366
Bhutan Tumching-La, 3800m April

Description

Rhododendron poluninii Davidian is a narrowly distributed eastern Himalayan shrub known principally from Bhutan and the adjacent ranges of the Indo-Tibetan border. It is documented from Tumching-La in Bhutan between 3400 and 3800 m, flowering in April, within the cool temperate to subalpine forest belt. The species grows on humus-rich, acidic slopes among mixed conifer and broadleaved woodland, in rhododendron thickets and along forest margins where ample atmospheric moisture from the monsoon and frequent cloud cover prevail. With a single GBIF record and no aggregated country list, it is among the rarer and most poorly documented members of the genus, reflecting both its localised range and limited botanical collecting in the region.

It is a small to medium evergreen shrub with stiff branchlets clothed, like the undersides of the leaves, in a dense indumentum of scales or hairs typical of its alliance. The leaves are coriaceous, elliptic to oblong, dark green and lustrous above and paler or rusty beneath. The flowers are borne in compact terminal trusses, each with a campanulate to funnel-shaped corolla in shades of rose-pink to pale magenta, five-lobed, subtended by deciduous bud scales; the stamens are ten and the ovary surmounted by a slender style. The fruit is a woody, septicidal capsule releasing numerous minute seeds.

Described by the Rhododendron specialist H. H. Davidian, R. poluninii commemorates the collector Oleg Polunin and belongs to the vast genus Rhododendron, the dominant element of Himalayan subalpine vegetation. Its extreme rarity in collections and apparently restricted range suggest it may warrant priority survey and assessment, as such narrow endemics are especially exposed to habitat disturbance, forest clearance and climatic warming of the subalpine zone.

Author: Davidian · Sources: POWO (Kew), GBIF, Flora of Bhutan, The Rhododendron Species (Davidian), Edinburgh Rhododendron monograph (Cullen & Chamberlain)

Ericaceae

Rhododendron pumilum

by GP Jürgens

Hook. f.

BhutanPG2011 549 1
Bhutan Ludlow-Sherriff-Trail Dem-Tso, 4700m July

Description

Rhododendron pumilum is a diminutive alpine shrublet of the eastern Himalaya and adjacent Sino-Himalayan region, recorded from China (Tibet, Yunnan), Nepal, India, Bhutan and Myanmar, with 115 georeferenced occurrences. It inhabits the high alpine zone, growing in damp turf, on mossy rocks, peaty banks and the margins of snow-fed meltwater seeps, typically between about 3500 and 4800 m. The species was photographed on the Ludlow-Sherriff Trail near Dem-Tso, Bhutan, at 4700 m in July, an elevation reflecting its strong association with the uppermost alpine meadows and moist micro-sites close to the limit of vascular plant growth.

It is one of the smallest rhododendrons, a creeping, mat-forming evergreen rarely more than 8 to 15 cm tall, with slender prostrate stems rooting at the nodes and minutely scaly young growth. The tiny leaves are obovate to elliptic, leathery, lepidote beneath with pale scales and often slightly revolute at the margin. The flowers are borne singly or in pairs at the shoot tips on relatively long pedicels and are nodding, broadly campanulate and pink to rose-purple, comparatively large in proportion to the plant; the stamens are typically ten and the style short and stout. The fruit is a small scaly capsule.

The species is placed in Rhododendron subgenus Rhododendron, section Rhododendron (subsection Uniflora), a group of cushion-forming dwarf lepidote species of the high Sino-Himalaya. Its solitary nodding flowers and creeping habit distinguish it from related dwarfs. Ecologically it is a specialist of cold, moist, well-aerated alpine substrates and an associate of cushion-plant communities. Though not assessed as globally threatened, its restriction to narrow high-elevation habitats makes it vulnerable to climate-driven habitat contraction.

Author: Hook. f. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, The Genus Rhododendron (Cullen & Chamberlain monograph)

Ericaceae

Rhododendron setosum

by GP Jürgens

D. Don

BhutanPG2011 242
Bhutan Tsochenchen 3800m June
BhutanPG2011 550 01 scaled
Bhutan Tsochenchen 3800m June, see also: Cassiope fastigiata
Bh09 6 P8
Bhutan Chele-La 3950m June

Description

Rhododendron setosum is a high-alpine dwarf shrub distributed through the eastern and central Himalaya, recorded from Nepal, India (Sikkim), Bhutan, and southern Tibet (China), with 507 georeferenced occurrences confirming a continuous arc along the main range. It is a characteristic plant of the upper alpine zone, forming low cushions and open mats on exposed ridges, moraines and the margins of dwarf-rhododendron heath, frequently above the treeline between about 3500 and 5000 m. It was photographed at Tsochenchen, Bhutan, at 3800 m in June and on the Chele-La pass at 3950 m, where it grows alongside Cassiope fastigiata in cold, peaty acidic substrates exposed to strong insolation and wind.

It is a much-branched, prostrate to ascending evergreen shrublet rarely exceeding 30 cm, the young shoots densely setose with stiff bristly hairs and gland-tipped trichomes that give the plant a strongly aromatic resinous scent. The small leaves are elliptic to oblong, leathery, glandular-scaly (lepidote) on both surfaces and bristly-margined, crowded toward the branch tips. The flowers, borne in small terminal clusters, are broadly campanulate to funnel-shaped and a vivid pink-purple to magenta, with a setose, glandular calyx and exserted stamens. The fruit is a small ovoid septicidal capsule.

The species belongs to Rhododendron subgenus Rhododendron, section Pogonanthum, a group of aromatic small-leaved lepidote rhododendrons centred on the Sino-Himalaya. Its glandular indumentum and powerful scent are diagnostic within this section. Ecologically it is a pioneer of disturbed alpine ground and a component of dwarf-shrub heath, tolerant of frost and intense radiation. Though locally abundant and not threatened, populations are sensitive to grazing and warming-driven shifts of the treeline.

Author: D. Don · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, The Genus Rhododendron (Cullen & Chamberlain monograph)

Ericaceae

Rhododendron succothii

by GP Jürgens

Davidian

Bh2008 243 P383
Bhutan Tumching-La, 3800m April
Bh2008 250 P395
Bhutan Tumching-La, 3800m April
Bh2008 251 P397 1
Bhutan Tumching-La, 3800m April

Description

Rhododendron succothii is an eastern Himalayan rhododendron with a narrow native range centred on Bhutan and the adjacent Indian Himalaya (Arunachal Pradesh), the roughly sixty-five GBIF records (with cultivated entries from Canada and Britain) reflecting both its restricted distribution and its presence in specialist collections. It grows in temperate rhododendron and conifer forest, on forest margins and open rocky slopes, generally around 3000 to 4000 m. The photographed plant from the Tumching-La in Bhutan at 3800 m, flowering in April, exemplifies its early-spring flowering in the upper temperate forest belt where it forms part of the dense montane rhododendron thickets.

The species is an evergreen shrub or small tree with stout, glabrous branchlets. The leaves are coriaceous, broadly obovate to broadly elliptic with a rounded to retuse and apiculate apex, glabrous and glaucous beneath, the venation impressed above and prominent below. The flowers are borne in compact terminal trusses; the corolla is tubular-campanulate and fleshy, deep crimson to blood-red, with five lobes and dark nectar pouches at the base, and the stamens are typically ten with a glabrous ovary and stout style. The fruit is a woody, cylindrical, curved capsule dehiscing to release numerous small seeds.

Rhododendron succothii is an accepted species placed in subgenus Hymenanthes (the elepidote rhododendrons) within Rhododendron (Ericaceae), allied to the red-flowered Himalayan species. Its glaucous foliage, fleshy crimson corollas and early flowering reflect adaptation to cool, humid temperate forest and bird pollination. Given its narrow eastern Himalayan range and habitat dependence, the species is of conservation interest and merits monitoring against forest disturbance.

Author: Davidian · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, Cullen & Chamberlain revision of genus Rhododendron (Ericaceae monograph)

Ericaceae

Rhododendron thomsonii

by GP Jürgens

Hook. f.

Bhutan2014 631
Bhutan Phobjika 2800m, May
Bhutan2014 632
Bhutan Phobjika 2800m, May
Bhutan2014 382
Bhutan Tongsa 2000m, May
Sikkim2004 307 P542
Sikkim/India May

Description

Rhododendron thomsonii is an Eastern Himalayan endemic centred on Sikkim, Bhutan, adjacent northeastern India, southern Tibet (China) and easternmost Nepal, with the nearly 479 records also reflecting widespread cultivation in Britain, North America and continental Europe. In its native range it occupies the cool, humid temperate forest zone, the images documenting plants at Phobjika around 2800 m and Tongsa near 2000 m in Bhutan, flowering in May, together with material from Sikkim. It grows in fir and mixed broadleaved forest, on forest margins, in rhododendron thickets and on open rocky slopes between roughly 3000 and 4000 m, often where the monsoon brings high atmospheric humidity.

It is an evergreen shrub or small tree reaching several metres, with smooth, flaking reddish-brown to plum bark. The leaves are broadly obovate to orbicular, glabrous, glaucous beneath, rounded or emarginate at the apex and cordate at the base, borne on short petioles. The inflorescence is a loose terminal truss of few flowers; the corolla is fleshy, broadly campanulate and a deep blood-red to crimson, subtended by a large, cup-shaped, persistent and conspicuously coloured calyx that is diagnostic for the species. Stamens are ten; the ovary and curved style are glabrous, maturing into a woody capsule.

The species was described by J.D. Hooker from his Sikkim Himalayan expeditions and is the type of subsection Thomsonia within Rhododendron subgenus Hymenanthes. Its large fleshy calyx, glaucous foliage and waxy red bells distinguish it from related taxa and have made it a foundation species in horticultural breeding. Though restricted in distribution, it is locally common within suitable montane forest and is buffered by extensive cultivation, so it is not regarded as globally threatened, although habitat pressures affect parts of its native range.

Author: Hook. f. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, The Genus Rhododendron (Royal Botanic Garden Edinburgh)

Ericaceae

Rhododendron trichocladum

by GP Jürgens

Franch.

Sikkim2011 211
Sikkim Yumthang 3500m, June
Sikkim2011 213
Sikkim Yumthang 3500m, June
Sikkim2011 218
Sikkim Yumthang 3500m, June

Description

Rhododendron trichocladum is a deciduous, scaly-leaved shrub of the eastern Himalaya and adjacent Sino-Himalayan ranges, distributed across south-western China (notably Yunnan and south-eastern Tibet), northern Myanmar and the Indian Himalaya, with GBIF records (553 occurrences) confirming a centre of abundance in Sikkim, Yunnan and Upper Myanmar. It occupies open hillsides, forest margins, rhododendron thickets and rocky slopes at roughly 2700-4000 m, frequently in cool, humid, moss-rich montane settings. The photographed plant from the Yumthang valley in north Sikkim at about 3500 m in June typifies its preferred sub-alpine zone, where it flowers as the snow recedes alongside dwarf rhododendrons and primulas.

A much-branched shrub usually 0.5-1.5 m tall, with thin, often bristly young shoots bearing scattered scales and setae. The thin, deciduous leaves are obovate to elliptic, bright green, sparsely scaly above and densely lepidote beneath, with ciliate margins and a short petiole. Flowers are borne in small terminal clusters of one to three, opening with or before the leaves; the widely funnel-campanulate corolla is yellow, often greenish-yellow and sometimes faintly spotted, with five lobes and a scaly outer surface. Stamens ten, declinate; the ovary is densely scaly, tapering into a slender style. The fruit is a small, ovoid, scaly capsule dehiscing septicidally to release minute winged seeds.

The species belongs to Rhododendron subsection Trichoclada (subgenus Rhododendron), a small group of deciduous, yellow-flowered, scaly-leaved shrubs characterised by their bristly indumentum. It is a valuable subject for cool temperate woodland gardens and has contributed to horticultural breeding. Though not globally threatened given its broad Sino-Himalayan range, populations are locally dependent on undisturbed sub-alpine scrub, making them sensitive to grazing pressure, fuelwood collection and habitat shifts driven by warming climates.

Author: Franch. · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, The Genus Rhododendron (Royal Horticultural Society monograph)