Ericaceae

Ericaceae

Cassiope fastigiata

Ericaceae

Rhododendron dalhousieae

Ericaceae

Rhododendron arboreum subst. cinnamomeum

Ericaceae

Rhododendron pendulum

Ericaceae

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 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)

Ericaceae

Rhododendron triflorum

by GP Jürgens

Hook. f.

Bhutan2014 357
Bhutan Tumching-La 3100m, May
Bhutan2014 402
Bhutan Yatong-La 2900m, May
Bhutan2014 403
Bhutan Yatong-La 2900m, May

Description

Rhododendron triflorum is an eastern Himalayan rhododendron distributed across China, Bhutan, India, Nepal and Myanmar, with about 484 GBIF occurrences (additional records abroad reflecting its popularity in cultivation). It grows in temperate forest, forest margins, rhododendron and conifer thickets and open shrubby slopes, generally between roughly 2700 and 3700 m. The plants photographed at Tumching-La (about 3100 m) and Yatong-La (about 2900 m) in Bhutan, both in May, exemplify its mid-montane forest habitat, where it flowers in late spring among mixed broad-leaved and coniferous woodland.

The species is an erect shrub or small tree with smooth, attractive coppery to reddish-brown, peeling bark. The leaves are evergreen, ovate to elliptic, glabrous above and conspicuously scaly (lepidote) beneath, the scales characteristic of the lepidote rhododendrons. The flowers are borne in small terminal clusters, typically in threes as the epithet triflorum indicates; the broadly funnel-campanulate corolla is pale yellow, often flushed or spotted with green, and densely scaly outside. There are ten stamens and a scaly ovary, and the fruit is a small dry capsule splitting to release numerous minute seeds.

Rhododendron triflorum belongs to subgenus Rhododendron (the lepidote, scaly-leaved rhododendrons), section Triflora, a group of slender-flowered species centred on the Sino-Himalaya. The lepidote indumentum and small capsular fruits with abundant wind-dispersed seed are characteristic of this clade. With a wide eastern Himalayan distribution the species is of least concern, and its handsome bark and yellow flowers have made it a valued ornamental; like its congeners it is an important component of the rhododendron-dominated temperate forests of the eastern Himalaya.

Author: Hook. f. · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, Annotated Checklist of the Flowering Plants of Nepal, Cullen revision of lepidote Rhododendron

Ericaceae

Rhododendron tsariense

by GP Jürgens

Cowan

Bh2008 223 G352
Bhutan Tumching-La, 3800m April
Bh2008 224 P355
Bhutan Tumching-La, 3800m April
Bh09 339 G553
Bhutan Jakar 3700m April

Description

Rhododendron tsariense is a shrub of the eastern Himalaya, restricted to China (south-eastern Tibet), north-eastern India and Bhutan, with a small number of records (66 occurrences in GBIF) reflecting its limited range. It inhabits high subalpine and alpine zones, growing in open coniferous and Rhododendron scrub, on rocky slopes, ridges and the margins of fir forest, characteristically between about 3000 and 4300 m. The photographed plants come from Bhutan, at Tumching-La (3800 m) and near Jakar (3700 m), flowering in April as the high passes emerge from winter, an elevation typical of the species' montane habitat.

It is a compact, much-branched evergreen shrub, the young shoots and undersides of the leaves clothed in a dense, felted, fawn to rusty-brown indumentum that is one of its most diagnostic features. The leaves are small, leathery, elliptic to obovate, dark green and somewhat rugose above. The flowers are borne in small terminal trusses; the corolla is campanulate (bell-shaped), creamy white to pale pink, often flushed rose and spotted within. The fruit is a woody dehiscent capsule, the persistent style and calyx remaining at the apex.

The species belongs to subsection Lanata (subgenus Hymenanthes), a group of indumented eastern Himalayan rhododendrons characterised by their conspicuously hairy leaf undersurfaces. Named for the Tsari region, it is a narrow-range endemic of conservation interest, its alpine populations potentially sensitive to climate shifts and to grazing and burning pressure in the high pastures. Like other rhododendrons it is bee- and bird-pollinated and forms ericoid mycorrhizal associations adapted to acidic, peaty mountain soils.

Author: Cowan · Sources: POWO (Kew), GBIF, Flora of Bhutan, The Genus Rhododendron (Cowan & Davidian), Edinburgh Rhododendron revision

Ericaceae

Rhododendron vaccinioides

by GP Jürgens

Hook.

Bhutan2014 811
Bhutan Wangdi Mo-Chu 1600m, May
Nepal 97 108 P184
Nepal Dongen 2400m April
Nepal 1994 196 ergebnis
Ost-Nepal Mewa-Khola
2100m April

Description

Rhododendron vaccinioides is a small epiphytic rhododendron of the eastern Himalaya and adjacent China and Southeast Asia, recorded from China, India, Myanmar, Nepal, Bhutan, Vietnam and Japan, with some 245 GBIF occurrences. It grows as an epiphyte on mossy trunks and branches, and occasionally on rocks, in humid temperate broadleaved and conifer forest, generally between about 1600 and 3000 m. The documented populations span Wangdi Mo-Chu in Bhutan at 1600 m, Dongen in Nepal at 2400 m and the Mewa Khola in eastern Nepal at 2100 m, flowering in April and May in the cloud-bathed mid-montane belt.

It is a small, much-branched epiphytic shrub with slender, often pendent or sprawling branchlets bearing scattered scales (lepidote indumentum). The leaves are small, obovate to oblanceolate and somewhat fleshy, clustered toward the branch tips, vaccinium-like in aspect, hence the epithet, and lepidote beneath. The flowers are small, solitary or few at the branch ends, with a short-tubed, broadly funnelform to rotate, white to pinkish corolla that is sparsely scaly outside. The fruit is a small lepidote capsule splitting into valves to release numerous minute seeds adapted to wind dispersal among the canopy.

The species belongs to Rhododendron subgenus Rhododendron, section Vireya (the largely epiphytic, tropical-montane rhododendrons), of which it is one of the few representatives reaching the Himalaya. It is widespread and not threatened, but as an epiphyte dependent on humid, moss-laden old-growth forest it is sensitive to deforestation and to drying of the montane cloud belt.

Author: Hook. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, Argent monograph of Rhododendrons of Subgenus Vireya