JARS v59n3 - Genus Rhododendron Status in Sikkim Himalaya: An Assessment

Genus Rhododendron Status in Sikkim Himalaya: An Assessment
Onkar N. Tiwari and U. K. Chauhan
School of Environmental Biology, A.P.S. University
Rewa (M.P.), India

Rhododendron flowers have an enormous range of colours, shapes and size in their wild form. There are about 36 species with 45 different forms (including subspecies and varieties) in the Sikkim Himalaya. Deforestation and unsustainable extraction of rhododendrons has led to severe pressure on the availability of these plants. The present study generates baseline information on status of the genus, which is perceived to be under varying degrees of threat with their natural habitat. Using IUCN guidelines for categorization 18 species are being considered as threatened/rare/endangered species. The rest of the species are out of danger at present; however, these species are also in localized conditions and may be wiped out, if the proper measures could not be taken.

The genus Rhododendron (Greek: rhodon = rose and dendron = tree) belongs to family Ericaceae and was for the first time described by Carl Linnaeus in 1837 in Genera Plantarum . Rhododendrons are the denizens of high altitude, comprising about 1,000 species mainly inhabiting a vast section of southeastern Asia stretching from northwestern Himalaya through Nepal, northeastern India, eastern Tibet, northern Burma and western and central China and south through Thailand, Viet Nam, Malaysia, Indonesia and the Philippine Islands; more than 90% of the world population of rhododendrons, including many species belonging to Vireya section of the genus, are from this region (Leach, 1961). The genus Rhododendron , having about 85 taxa in India, according to current calculations, is mainly distributed in the Himalaya region (one species R. nilagiricum in South India), out of which a total of 36 species with 45 different forms including subspecies and varieties occur in Sikkim alone.
Sikkim Himalaya, which extends between 270 03'41" to 280 7'34" North and 880 3'40" to 880 57' 19" East, is defined by the great drainage region of the river Tista that constitutes the hill of Sikkim (7096 km2) and Darjeeling Gorkha Hill Council area of West Bengal (3149km 2 ) range altitudinally from 100m above mean sea level (amsl) (foot hill) through 4000m amsl (timberline) up to 8548m amsl (Mt. Khangchendzonga). The area thus covers several ecological zones, viz., subtropical, temperate, subalpine and alpine. In such a small area sharp climatic differences in different ecological zones have promoted a rich diversity and variations in Rhododendron species. Sikkim is rich in cultural and biological diversity. Lepachas, Bhutias, Limbus and Nepalese are the main ethnic group of Sikkim and they differ from each other in their food habits and life style, which also play a major role in survival and conservation of Sikkim Himalayan rhododendrons.
Rhododendrons have a characteristic slow growth rate. Another characteristic of the genus is the range in size from tiny mat-like plants in the alpine region ( R. pumilum ) a few centimeters tall to giants 25 meters ( R. arboreum ). Our preliminary exercise shows that about 98% of the Indian species are found in the Himalayan region out of which 72% are found in Sikkim Himalaya. The genus forms a very important dominant combination of forest types in cool temperate and subalpine regions, and also on the alpine meadows of the Sikkim Himalaya. It supports a wide range of biodiversity; therefore, this genus could be regarded as a keystone element in these high altitude areas and, if disturbed, can degrade habitats that threaten associated biodiversity. It also provides food preserves for a wide range of birds. In the subalpine to alpine transition zone that includes the timberline in the most fragile ecosystem in the Sikkim Himalaya Rhododendron is the only group of plants that has continuum in the aforesaid ecotone and, beyond doubt, maintains the biological sustenance in this fragile zone.
The purpose of this study was to provide baseline information, the species potential and information on extent of availability and quantity. The number of species of Sikkim Himalayan Rhododendrons has been a constant source of problems to many workers. Sometimes cited as low as 29, and high as 36, the total number of species keeps moving up and down (Hooker, 1849; Clarke, 1875; Philipson & Philipson, 1975; and Chamberlain, 1982). These workers also describe individual species. Various expeditions were done by the workers for enumeration of rhododendrons and search of various species (Pradhan, 1985,86; Lave & Smoerum, 2001). A survey of various threatened plants in the Sikkim Himalaya and the search for various species were also carried out (Justice, 2000; Maiti & Chauhan, 2000). In the latest work Pradhan & Lachungpa (1990) have assessed the whole area with a total of 36 species with a remarkable number of various subspecies, varieties and forms; this gives a more or less complete picture. However, some taxa such as the five varieties of R. cinnabarinum as well as R. lepidotum may require quite some more work. No doubt previous observers have made note of it but the number of forms was small. The present study corroborates the taxa of the previous workers with, of course, a few modifications.

Material and methods
Extensive field visits were made to different sites at north Sikkim (Singba, Yumthang, Lachung, Lachen), east Sikkim (Kyongnosla, Tsangu, Kupup, Rate-Chu), west Sikkim (Bersey, Tshoka, Dzongri), Gangtok and the adjoining area, Neora Valley National Park and Singalila National Park (Darjeeling Gorkha Hill Council Area of West Bengal) during 2001-2002. Different rhododendron species were identified and enumerated. Individual species were studied for their field character, habitat, morphological characters, flowering and fruiting, availability and for distribution pattern, etc. The major references were: Hooker, 1849; Philipson & Philipson, 1975; Cullen, 1980; Chamberlain, 1982 and Pradhan & Lachungpa, 1990. Observations made were recorded and compared with the available data of previous workers.

Baseline Assessment: Over a century the rhododendrons in the region have been treated as per the requirement of the time, by different workers in different forms. Taxonomy and systematics apart relatively few study cases on its growing condition and range are available till now. Some workers have seen a part and interpreted accordingly and, likewise, some have covered a particular land course and their views are differently given. Not only have we noted different account on the forms, habit, habitat and many other aspects but a few are controversial and yet to be fully appraised. The different species of rhododendrons of the region are discussed and described in this section.
The Species Number: The number of species of Sikkim Himalayan rhododendrons has been a constant source of problems to many workers. Quantifying the genus is perhaps the first important step towards simplification. Sometimes cited as low as 29 and as high as 36, the total number of species keeps moving up and down. The total number of species recorded at various times and places by different workers shows in Table 1.

Table 1: Rhododendron species from Sikkim Himalaya
Workers Hooker Clarke PPCC* Pradhan & Lachungpa Present Study
Types (1849) (1875) (1975, 1980, 1982) (1990)
Species 33 29 31 36 36
Subspecies 13 - 03 10 09
Varieties 08 04 01 07 07
Forms - - - 06 06
Total 54 33 35 59 58
* Philipson & Philipson, Cullen and Chamberlain

Usually, the actual reason was found to be the systematics itself for altering the total count. After the original work each closer examination reveals more details and further breakups and/or clumping among the plants occurring, eventually given out different tallies.
Species Note: Individual species are described here along with pertinent information to each. Different views wherever appropriate are incorporated with citation. Distribution given (in altitude) is either as examined personally or as noted by the different workers and place names as in the original text. Observations made for special cases were recorded.
R. aeruginosum Hook. f. [Local (Nepali) Name: Nilo-Pate-Chimal]: First report - Hooker(1849). Distribution - Lachung and Yumthang (in black open rocky places), 4500-5000m amsl (above mean sea level). Found in Sikkim and Bhutan. Transferred to intraspecific rank as R. campanulatum subspecies aeruginosum (Hook, f.) Chamberlain. Flowering - May to June; Fruiting - September to October. This is a distinct species, which belong to the Campanulata subsection of section Hymenanthes. Elliptic shaped, matt bright green leaves that have recurred margins and bear thick rusty tomentum on the undersurface can distinguish it from other. The flowers in shape and size approach R. campylocarpum , though of deep rose pink, flushed with red externally. The buds are devoid of scales, hairs or glands.
R. anthopogon D. Don [Local Name - Dupi Gurans]: First report - D. Don (1821). Distribution - Bakhim, Dzongri, Gomathang, Megathang, Lachen, and Lachung, 3000 to 5500m amsl. Flowering - May to June; Fruiting - September to October. Dwarf aromatic shrub plant attaining 300 to 450mm in height with short twiggy branches. It inhabits open rocky situation or edges of rhododendrons forest. Subspecies anthopogon - type Nepal (Cullen and Chamberlain, 1978) also noted by Hooker (1849) and Pradhan and Lachungpa (1990). Subspecies hypenanthum - noted by Pradhan and Lachungpa (1990). Also in rare variety album . The flower is pure white instead of flushed pink.
R. arboreum Smith [Local Name - Lali Gurans]: First report - Hardwick in Siwalik Mountains in Kashmir (1796), described by Smith (1805). Distribution - Most of the areas in Sikkim Himalaya between 1700 -3400m amsl. Inhabits open forests and rocky slopes. Flowering March to May; Fruiting - September to October. This is the national tree of Nepal. Subspecies - R. arboreum ssp. cinnamomeum (as cited by Pradhan and Lachungpa). Varieties (a) cinnamomeum (Wall. ex) Lind; (b) roseum of Lindley. R. arboreum var. compbelliae is another taxon used by Pradhan and Lachungpa as subspecies. Hooker also enumerates R. arboreum var. campbelliae . This is a taxon which is not clear. R. arboreum is an extremely variable species, especially with respect to leaf shape and leaf indumentum, with a wide geographical distribution. Through the former subspecies arboreum predominates below 2500m and subspecies cinnamomeum above 2900m amsl. It is also difficult to distinguish some forms of subspecies delavayi from subspecies cinnamomeum . The two isolated subspecies, zeylanicum and nilagiricum , are closer to one another than they are to subspecies delavayi , from which they are clearly divided. Natural hybrids occur between var. roseum and three other species R. barbatum , R. campanulatum and R. wallichii (Cullen).
R. baileyi Balf. f. [Local Name - Bailey ko Chimal]: First report - Balfour. f. (1919) at River Tsangpo in southren Tibet. Distribution - Yumthang en route, hillsides, screes and rocks (3000 to 4250m amsl). Flowering - May to June; Fruiting - September to October. It is conveniently identified in the field even when not in bloom by the yellowish brown scales covering the plant.
R. barbatum Wall.ex G. Don [Local Name - Lal Chimal]: First report - Wallich from Gossainthan in Nepal and described by G. Don in 1834. Hooker described this in 1849, Tonglu in Darjeeling hills, in open slopes, amongst scrub, Abies forest, etc., distributed between 2700-3700m amsl. Flowering - March to April; Fruiting - August to September. R. barbatum may or may not have bristles. Both kinds have been found growing side by side at Yakchay in northeast Sikkim. Closely allied to R. smithii . Natural hybrids between R. barbatum and R. arboreum are recorded. Var. smithii (Nutt ex Hook. f.) - It is found in Singlalila range in Sikkim and in Nathula at 3400 to 3500m amsl, in flower during May. Available var. allied to R. exasperatum and R. barbatum . This is the one of the most beautiful of Sikkim Himalayan species. Basically branched tree usually 6 meters tall and possessing smooth purplish-red bark, which peels off in large flasks. Flower scarlet-red, in rounded heads 100-150mm across.
R. campanulatum D. Don [Local Name - Nilo Chimal]: First report - D. Don (1821). The hill folk call this Nilo Chimal literally meaning blue rhododendron. A very common species at 3000 to 4000m amsl, bearing lax trusses of 8-12, 4-5cm, across, bell shaped flowers, which are usually lavender to rose or rarely white in colour. Mainly distributed in Nathula, eastern Nepal through Sikkim. Specimen flower was observed in Yumthang near the spring. The leaves are supposed to have medicinal properties. Flowering - May to June; Fruiting - July to August. This may not be a hybrid of this swarm because all the plants bear almost the same age. Could be a mutant. R. campanulatum var. album is figured in Pradhan and Lachungpa but citation text could not be found. In fact R. campanulatum shows marked differentiation in corolla colour. The mauve ones occur in majority at the Singalila ridge and the purple coloured ones are predominant in the Lachung Valley. Subspecies - aeruginosum (Hook. f.) Chamberlain. Found in alpine slopes (3800 - 4500m). Overlapping and hybrids are found.
R. camelliiflorum Hook. f. [Local Name - Chia-phule Gurans]: First report - Hooker (1849). Mainly distributed in Tsangu and Nathula area of eastern Sikkim, has white flowers with pinkish tinge. The flowering time falls during the monsoon months during June to July and this coupled with heavy leech infestation makes collection of specimens an arduous task. So it gets natural protection essentially dictated by its flowering habit. The lovely leaves and dwarf habit and flowers make this species a desirable garden plant for milder temperate climate. Population of this species could be badly affected during clear felling of primarily forests, mainly because of limited distribution. Hence some areas of its occurrence deserve special protection. Usually grows at elevation of 2500 to 3500m in association with ferns, Utricularia and other epiphytic flora.
R. campylocarpum Hook. f. [Local name - Bango-phale Gurans]: This is a curved-fruited rhododendron, first reported by Hooker(1849). It's a charming species with sulfur yellow flowers borne on rounded bushes covered with bright green foliage. The flowers are honey scented while the glandular hairs on the leaf stalk, calyx and capsules emit a resinous odour. This species inhabits rocky outcrops and spurs in association with R. thomsonii , and R. campanulatum . Distributed mainly in western Sikkim (3200 - 4000m). Flowering - May to June; Fruiting - August to September. R. campylocarpum var. elactum is figured but citation text is missing. In 1892, a plant of this species bearing flowers was awarded the first class certificate of the Royal Horticultural Society, London (Pradhan and Lachungpa, 1990).
R. ciliatum Hook. f. [Local Name- Junge Chimal]: First report - Hooker (1849). Mainly distributed in inner ranges of the Sikkim Himalaya (3000-3800m). This is a superb species so named because of the leaves, calyx and pedicles which are fringed with hairs. Fragrant dwarf shrub up to 1.5m high inhabiting wet moist rocky places or marshy ground in fully exposed places in association with R. niveum , R. barbatum and Primula denticulata . I have also seen this species in and around Lachung and Lachen in northeast Sikkim. Flowering - April to May (~ June); Fruiting - July to August.
R. cinnabarinum Hook. f. [Local Name- Sano Chimal]. A prominent species in Sikkim at elevation of 3500 to 4500m amsl. The cinnabar red flowers combine well with the beautiful grayish green foliage making it a very desirable plant for the temperate gardens. We noted that in the Singalila Ridge of Darjeeling it showed most flowers to be of dark to scarlet-red colour, while these in northeast Sikkim had smoky salmon to cinnabar red colour. Though it is a lovely plant, the leaves and the stamens are reported to be very poisonous. Flowering - April to May; Fruiting - July. Five varieties enumerated (Pradhan and Lachungpa): R. cinnabarinum var. aestivale , var. blandfordiiflorum , var. roylei , var. pallidum , and var. purpurellum . All of these are available or not in the region not very clear.
R. dalhousiae Hook. f. [Local Name - Lahare Chimal]: First report - Hooker (1849) ( Darjeeling). Found on steep banks, rocks and trees of Michelia and Quercus, growing mostly epiphytically in association with ferns, orchids, etc., distributed in Sikkim Himalaya at an elevation of 1500 to 2500m amsl. The local cowherds know it as the dreaded Lahare Chimal, which they do not feed to cattle for the plant is very poisonous. Thus this plant is naturally protected from its predators and the only damage occur to it is from habitat destruction. Flowering - April to May; Fruiting - August to September. Subspecies tashii (Sikkim population) occurred in Pangthang, Chumgthang and in Lachung northeast Sikkim. This subspecies bears creamy white flowers deeply suffused by yellow inside and striped conspicuously on the outside with red. (var. rhabdotum is earlier recorded from Bhutan and Assam; however, we have also noted some plants in Rate Chu catchment area near Gangtok).
R. decipiens Lacaita [Local Name - Jhukaune Korlinga]: First report - Lacaita (1916). Collected between Chiabhanjyang and Singalila ridge. Mainly inhabitant in rich humus under shade of Abies in association with R. hodgsonii at the elevation of 3300 to 3800m amsl in Lachung, small trees attaining height of 2.5 to 3.0m and very similar to these of R. hodgsonii but easily distinguished as the bark of R. decipiens does not peel off quickly as with R. hodgsonii and hence encourages growth of lichens and mosses with which the trunk and branches are found covered. Flowering - May to June; Fruiting - October to November. (On studying the specimens carefully, the 10 stamens, open corolla and 8-celled ovary clearly indicated its own right as a species, although it is generally considered to be a natural hybrids between R. hodgsonii and R. falconeri ).
R. edgeworthii Hook. f. [Local Name - Edgeworth ko Chimal]: First report - Hooker (1849). Found in the inner ranges of Sikkim Himalaya, particularly in Lachen (2000 -4000m). Variable in size and habit across a very wide distribution; the variation, however, is not amenable to taxonomic recognition. Mostly grows epiphytically. It is one of the finest Himalayan species, which combines the qualities of excellent foliage and large flowers richly coloured white tinged pink/pale yellow). Flowering - May to June; Fruiting- October to November.
R. falconeri Hook. f. [Local Name - Korlinga]: First report - Hooker (1849). From the characteristic rhododendron forest at the elevation of 3000-3500m in the Sikkim Himalaya. An impressive tree recognized in the field by the cinnamon coloured peeling bark, rufous and matted leaf surface thickly covered beneath with rusty indumentum. Flowers borne in round clusters of 20 - 25, creamy yellow blotched with purple at the base. Flowering - April to May; Fruiting - August to September. Subspecies falconeri - type; Northern India (Hooker), Lachung, Lachen and Thsoka.
R. fulgens Hook. f. [Local Name - Chimal]: First report - Hooker (1849). This is a rare species found above 4000m (i.e., above the range of occurrence of R. barbatum ). Grows in rich humus in association with R. aeruginosum at upper ridge of Sikkim Himalaya. A shrub carrying bright green young branches. The plant is free of glands, hairs or scales except the floral bract and young foliage, which has shaggy hairs. Flowers dark blood to scarlet, rather fleshy, tubular bell shaped. Flowering - May to June; Fruiting - October.
R. glaucophyllum Rehder [Local Name - Takma Chimal]: First report - Described by Hooker as R. glaucum unaware that his description had been preceded by that of Rehder (1848). Distribution above 2700m, though not easily traceable. Flowering - April; Fruiting - June to July. The tubular flowered form known as var. tubiforme as well as the usual forms are both found in northeast Sikkim, though both are rather rare occurrences (Pradhan and Lachungpa, 1990). The variety R. glaucophyllum var. tubiforme is described as "type" Assam. However in my personal observation R. glaucophyllum is not a rare species as far as Sikkim Himalaya is concerned. This species does not warrant a rigorous workout to make it appear different and into so many taxa.
R. grande Wight [Local Name - Patle Korlinga]: First report - Wight (1847). Hooker (1849) as syn. R. argentum Hook.f. type; Sikkim summit of Sinchel, Suradah and Tonglue. It forms main forests in and around Sikkim at 2000 to 3000m especially on summit of Mt. Tonglue, forest of Sinchal, Sandakphu and Damsong in Darjeeling, between Chungthang and Lachen, Lachung and Perk Chu. Forming characteristic rhododendron forests at these altitudes. It is a magnificent species bearing large trusses of creamy white to white flowers atop ornamental shiny foliage. Flowering - March to April; Fruiting - July.
R. griffithianum Wight [Local Name - Seto Chimal]: First report - Wight (1850); syn. R. aucklandi Hook.f. (1851). It is found in open mixed woodland with R. grande , Magnolia globosa , etc. It is reported very common in Bhutan, and also found in Lachung Valley and Chungthang of North Sikkim (2100 - 2900m amsl). A distinctive species on account of its well developed calyx, etc., without close allies (Chamberlain, 1982). Flowers are mildly scented. Flowering - April; Fruiting - June.
R. hodgsonii Hook. f. [Local Name - Gulabi Korlinga]: First report - Hooker (1849). Type; Sikkim Himalaya. This species forms primary forest at elevation of 3000 - 4000m amsl in association with R. cinnabarinum , R. decipiens and R. campanulatum growing in rich humus. A small, common, basically branched, spreading tree, identified by the pinkish brown bark which peels off in flaps. The glossy spreading leaves are of brilliant green colour and have silvery gray undersides. In winters they roll up and hang in pendulous fashion from tips of the branches. Readily identified during the flowering season by the large heads of crimson to rose-purple bell shaped flowers. Flowering - May to June; Fruiting - September.
R. lanatum Hook. f. [Local Name - Bhutle Gurans]: First report by Hooker (1849) in Dzongri at 4000m amsl. It is a common species in Dzongari and Chola in western Sikkim and Nathula in east Sikkim, though north of Nathula it appears to be scarce. This is a species with considerable local geographical variation. The tree can be identified conveniently even from a distance by the dark grayish bark and the leathery, obviate, dark green leaves covered thickly with fawn felt on the underside. The leaves are grouped in 3-5 and appear somewhat twisted. The crimson to red spotted sulfur yellow bell shaped flowers are noticeable for size and colour and borne on loose terminal corymb of 6-10. Flowering - May to June; Fruiting - September.
R. lepidotum Wall. ex G. Don [Local Name - Bhule Sunpate]: First report - Discovered by Wallich and described by G. Don (1834), as R. elaegnoides by Cullen (1978). Commonly found on open rocky situation at 2500-5000m elevation in Sikkim Himalaya. This species is recognized in the field from other related dwarf species like R. setosum and R. nivale by its leaves that are larger in size and the flatly open flowers which are borne on pedicels 20 -30mm long). It varies in colour from deep yellow to crimson, bears 8 stamens and short thick, downward-bent style. R. lepidotum consists of extremely variable group of plants, which could, as done earlier by Hooker and later by Stevenson in Species Rhododendrons published by the Royal Horticultural Society, London in 1930, easily be taken for separate species. Our field observation in Chungthang in northeast Sikkim, the type locality of R. lepidotum var. salignum , shows it to be a distinct entity, although not recognized in the Edinburgh Revision. Occurring at lower elevations and quite apart in its leaves and flowers, it can be taken to represent R. lepidotum in its extreme form to merit a subspecific rank. The large population we came across of this variation at Chungthang, not differing much in the willow-like leaves, the greenish yellow flowers with rather star-like appearance as in azaleas, and the early flowering (May to June) habit readily distinguishes it from the other forms of R. lepidotum , previously known as R. obovatum and R. elaeagnoides ) by the round flowers and the obovate elliptic leaves. It may be mentioned here that the above species have been included in all recent literature (Pradhan and Lachungpa, 1990); R. lepidotum var. obovatum (Hook.f.), although not in the Edinburgh Revision, 1996. Flowering - June to July (to October for var. salignum ); Fruiting - October.
R. lindleyi T Moore [Local Name - Sano Lahare Chimal]: First report by T. Moore in Gardener's Chronicle (1864). Found epiphytic on trees and rocks and mainly distributed in West Sikkim at an elevation of 2000 to 3000m amsl. This species shows close affinity and resemblance to R. dalhousiae but it is a distinct species easily recognized by the absence of bristly shoots, the tubular funnel shaped, highly fragrant flowers, short 8mm-long anthers and the calyx which is fringed with soft white hairs. Flowering - April to May; Fruiting - August.
R. leptocarpum Nuttall [Local Name - Jhinophale Gurans]: First report Nuttal (1854), syn. R. micromeres Tagg (1930). Mostly inhabits trees growing in association with R. dalhousiae and R. camelliflorum . In Sikkim it has been reported recently by Barry Starling (1984) from Tshoka village in Dzongri of west Sikkim growing on rotting tree stumps at 3400m amsl. Flowering - July; Fruiting - October.
R. maddenii Hook. f. [Local Name - Major Madden ko Chimal]. First report - Hooker (1849), thickets at Chungthang. Distribution: Found in higher reaches of Gangtok at Rate Chu catchment area at 2000 to 2500m amsl, epiphytic on trees and rocks. Pradhan and Lachungpa (1990) have also seen this species in Choongthang at the confluence of the rivers Lachen and Lachung on steep, rocky, precarious slopes and thickets; however, we were never be able to found this species in this area except Rate Chu. This is an endemic species of Sikkim and Bhutan. Subspecies crassum has been naturalized at lower elevation in Gangtok and Chandra Nursery of Rhenock in Sikkim. Being scarce and localized in few places, it needs state protection and propagation. Flowering - June to July; Fruiting - November.
R. nivale Hook. f. [Local Name - Hinu Gurans]: First report - Hooker (1849). No other flowering shrub in the world attains the altitude (4500 to 6000m amsl) that R. nivale reaches, and is the most tenacious among flowering shrub (Pradhan and Lachungpa, 1990). In Sikkim Himalaya this species found in open mountainsides, screes, up to 5800m amsl (Hooker, 1849). Described by Hooker as "the highest growing shrub in the world with the latest to bloom and earliest to mature its seeds." Flowering - July to August; Fruiting - September.
R. niveum Hook. f. [Local Name - Hinu Pate Gurans]: First report by Hooker (1849), type habitat in Lachung, Lachen and Chola in north Sikkim. It is endemic to Sikkim and Bhutan (2900 to 3650m amsl). This is the state tree of Sikkim. This is a distinctive species with its close ally R. arboreum , but close study reveals that they are separate in both foliage and flowers. The smoky blue or purple-mauve flowers and snowy underside of the leaves which turns grayish brown with age readily distinguishes it from R. arboreum . Flowering - April; Fruiting -July.
R. pendulum Hook. f. [Local Name - Jhundinae Chimal]: This species comes very close to R. camelliiflorum in its rotate flowers and epiphytic habit but in other respects both differ remarkably from one another. A scentless species, it is not quite easy to detect except when it comes to bloom in the month of April to May. The plant that was described in 1849 by Hooker came from Lachen in North Sikkim. It mostly grows in sheltered abies forest epiphytic and pendulous from trees of Abies spectabilis and A. brunoniana , and also on sheltered rocks at 3300 to 3400m amsl in Yakchey and Phuni between Lachung and Yumthang in north Sikkim. Fruiting - August to September.
R. pumilum Hook. f. [Local Name - Purke Gurans]: First report - Hooker, 1849. This is the dwarfest rhododendron found in Sikkim but is nevertheless one of the most elegant and rare species. Easily recognized in the field by its dwarf prostrate habit and bright bluish green elliptic leaves, which are scaly and glaucous beneath. Associates and grows from massy mats on avalanche slopes (Pradhan and Lachungpa, 1990). Flowering - June to July; Fruiting - November.
R. setosum D. Don [Local Name - Tsallu Gurans]: Discovered by Buchanan Hamilton in Nepal and described in 1821 by D. Don. It is a dwarf plant inhabiting the higher mountain slopes above 3000m amsl. Like all higher alpine plants, it is late to flower (June to July) and early to set seed (October). This is the tsallu of the sikkimese, a plant which emits such intense aroma at the high altitudes on sunny days that discomfort and headache it causes is often unbearable. Frequently inhabits summits of high passes growing on open rocky situation gregariously, in association with other high altitude species like R. nivale , R. lepidotum , etc., at 3000 to 5000m amsl. It is a quite a common species in Sikkim Himalaya.
R. sikkimense Pradhan and Lachungpa [Local Name - Sikkimae Gurans]: First report- Pradhan and Lachungpa (1990), at Phuni area of North Sikkim (3700m). Mostly inhabits in open exposed area having gravelly sandy soil in association with R. thomsonii and R. campanulatum . This species can be distinctly identified from all other even from the tree habit, which is very branched and spreading. Flower blood red, like those of R. thomsonii . This is quite rare species and endemic to Phuni area. Flowering - May to June; Fruiting - October.
R. thomsonii Hook. f. [Local Name - Dr. Thomsen ko Gurans]: First report - Hooker (1849). Very common species in Sikkim (3300-4500m). In some places in north Sikkim, especially in Shingba north of Lachung, it is abundant and has possibly hybridized with other species to produce hybrid swarms as intermediate characters are evident in quite a number of the cases. Conveniently recognized in the field by its smooth bark which supports the growth of Usnea mass , and the near round to elliptic foliage which during the spring and early summer covers the landscape with glaucous blue hue. Flowers are waxy, fleshly, usually blood red but forms of crimson and almost blackishred are occasionally found. Flowering - May to June; Fruiting - August. Subspecies candelabrum (Hook.f.) Chamberlain in notes R.B.G. Edinb. 36(1): 121(1978). It differs from R. thomsonii in bearing shorter calyx, pale pink to orange flowers of smaller size.
R. triflorum Hook. f. [Local Name - Pahenle Chimal]: First report - Hooker (1851). Inhabits open slopes appears to be fairly scattered though in small numbers in Sikkim near Lachung, and grows in association with R. thomsonii and other species (2300 to 4000m). Flowering - April to June; Fruiting -?
R. vaccinioides Hook. f. [Local Name - Khianuae pale Gurans]. This is only representative of the Vireya section of rhododendron in the Sikkim Himalaya. The flowers are amply compensated by the magnificent stiff, leathery, shiny foliage that is shaped like a spatula. Inhabits moist rocks and shady aspects of trees in association with Vaccinium obovatum and Agapetes serpens . In northeast Sikkim it is of rare occurrence and was seen only twice - one near Lemma and other Tshangu lake in Nathula at an elevation of 2400 to 3400m amsl. Flowering - April to May; Fruiting - August.
R. virgatum Hook. f. [Local Name - Hanginae Gurans]: First report - Hooker (1849). Inhabits gregariously on freshly exposed steep in Chungthang, Lachung and Lachen between 2500 to 3300m amsl. It is growing in association with Primula and Drosera species. Flowering - May; Fruiting - July. Subspecies oleifolium found in North Sikkim (Pradhan & Lachungapa, 1990).
R. wallichii Hook. f. [Local Name Dr. Wallich ko Chimal] First report - Hooker (1849). Synonym R. campanulatum var. wallichii (Pradhan & Lachungapa, 1990). Found between Lachung and Yumthang in interior north Sikkim at 4000- 5000m amsl. The species can be identified through presence of calyx, the broadly bell shaped flowers, and the powdery ferrugineous hair tufts on the surface of the leaves which do not form a continu ous indumentum, all of which identifies it from the closely related R. campanulatum. Flowering - June; Fruiting -?
R. wightii Hook f. [Local Name - Dr. Wight ko Gurans]: First report - Hooker (1851). It is a beautiful and floriferous bearing large cream-yellow or white flowers in May - June, fruiting in September. Abundant in between the elevation of 4000-4500m. R. wightii grows in the valley often very close to flowering rivers forming dense thickets in association with R. campanulatum and R. fulgens .

Table 2: Sikkim Himalayan rhododendrons: habits.
Epiphytes / Lithophytes Brush / Brushlets Shrubs Trees
R. camelliiflorum R. anthopogon R. aeruginosum R. arboreum
R. dalhousiae R. ciliatum R. baileyi R. barbatum
R. edgeworthii R. lepidotum R. campanulatum R. decipiens
R. griffithianum R. nivale R. campylocarpum R. falconeri
R. leptocarpum R. pendulum R. cinnabarinum R. grande
R. lindleyi R. pumilum R. fulgens R. hodgsonii
R. vaccinioides R. setosum R. glaucophyllum R. wightii
R. virgatum R. lanatum
R. maddenii
R. niveum
R. sikkimense
R. thomsonii
R. triflorum
R. wallichii

Comparative notes on morphological characters:
(A) Habit:
A broad division among the Sikkim Himalayan rhododendron may be done as epiphytes and terrestrials. Among the terrestrials three different life forms are trees, shrubs and brush/brushlets. The 36 species are depicted as per their habits (Table 2).
(B) Leaves: A typical rhododendron leaf is lanceolate in shape, short-petioled and with an acute leaf tip. However, variation between the species and its various intraspecific taxa is obvious. The variation in size is one of the most remarkable features. Structure wise, the leaves are never filmy or thin but rather glabrous in constituency; almost all are glaucous. The variation within species is also note worthy (e.g., R. arboreum var. arboreum and var. cinnamomeum ; R. lepidotum subsp. salignum and obovatum , etc.). The high altitude members emit resinous odour from the leaves and tender twigs (e.g., R. anthopogon , R. nivale and R. setosum ). During winter some of the species exhibit leaf curling which regain their normal leaf shape at the onset of autumn; winter season also may damage the leaf. The curling may be on the lateral side (e.g., R. fulgens , R. lanatum , etc.) or it may start from tip upwards (e.g., R. hodgsonii ). R. pendulum and R. lanatum are two species which exhibit dense pubescence on the undersurface of its leaves. All these visible structural characteristics may be employed to fend the plant from severe winter, snow and transpiration. The general shape of the leaf is, of course, lanceolate but the tendency is towards ovate rather than to the linear shape. Petiole is short, mostly thick and strong.
The leaf size range against altitude offers no significant relationship. On a general observation species out in the open are smaller leaved and shade growing species (under canopy or other natural sheds) bear larger leaves. The situation may also be interpreted in terms of ambient moisture dry zones inducing small leaf size ( R. nivale ). The largest leaf is 188 times greater than the smallest one found ( R. falconeri [300 x 150mm]; R. nivale [6 x 4mm]). Comparison of some anatomical features of leaves of rhododendron species is given in Table 3.

Table 3: Comparison of anatomical features of some rhododendron species.
Parameters R. niveum R. maddenii R. pendulum
Leaf size (mm) 325 x 125 125 x 35 54 x 20
Leaf thickness (mm) 1.1 1.2 1.3
Stomatal frequency (stomata/mm 2 ) 328 318 288
Specific leaf mass (mg/mm 2 ) 226 250 302

(C) Scales: The scales are minute structural characters on a rhododendron leaf. In a broad sense, the rhododendrons are classified into scaly leaved (lepidote) and non-scaly leaved (elepidote). The scale-bearing rhododendrons are normally recognized as those belonging to rather alpine type of climate. The dryness, low temperature and high winds characterize this type of climatic domain and the resultant specialization in leaf anatomy. The two types of rhododendrons for Sikkim Himalaya are grouped in Table 4 and its occurrence along with altitudinal gradient Table 5.

Table 4: Lepidote and elepidote rhododendron species in Sikkim Himalaya.
Lepidote Elepidote
R. anthopogon R. arboreum
R. baileyi R. barbatum
R. camelliiflorum R. companulatum
R. ciliatum R. campylocarpum
R. cinnabarinum R. decipience
R. dalhousiae R. falconeri
R. edgeworthii R. fulgens
R. glaucophyllum R. grande
R. lepidotum R. griffithianum
R. leptocarpum R. hodgsonii
R. lindleyi R. lanatum
R. maddenii R. niveum
R. nivale R. sikkimense
R. pendulum R. thomsonii
R. pumilum R. wallichii
R. setosum R. wightii
R. triflorum
R. vaccinioides
R. virgatum
Table 5: Number of lepidote and elepidote species along with altitudinal gradient.
Altitude (m amsl) Number of Species
Lepidote Elepidote
1500-2000 04 03
2001-2500 10 03
2501-3000 15 08
3001-3500 17 12
3501-4000 15 11
4001-4500 11 11
4501-5000 06 06
5001-5500 03 03
Table 6: Variation of corolla in the rhododendrons of the Sikkim Himalaya.
Type of Corolla No. of Species
Companulate 26
Flat 07
Reflexed 02
Tubular 01

(D) Flowers: The flowers are mostly a typical pentamerous, gamopetalous affair. The form changes in respect to size, shape, colour and also in terms of sepal, petals, androecium and gynoecium. Variation where the petals cease to build a tubular structure are found in R. camelliiflorum , R. lepidotum , R. triflorum , R. virgatum , etc., which move towards a more flat figure in R. baileyi and R. leptocarpum with an extreme polypetalous (free corolla) condition in R. vaccinioides .
Size also differs from the largest ( R. griffithianum ) to the smallest ( R. vaccinioides ) by a ratio of 110:8. The relationship of flower was found to be sympathetic with its respective habitat of niche rather than with altitudinal succession. So far, the colour and shades assigned to the rhododendron flowers have been found to be in an arbitrary way. As each one has a different idea of one's colour perception different colour assignment may be found when these are compared. Table 7 shows comparison of rhododendron flower colour by different workers. A collective data on flowering and fruiting period at different altitude is given in Table 8(a & b).

Table 7: Flower colour estimation of rhododendrons of Sikkim Himalaya by different workers.
Species Hooker (1849-51) Clarke (1875) Gamble (1936) P&P, C, C* Pradhan & Lachungpa (1990) Present Study
R. aeruginosum Deep rose pink - - Deep reddish pink Deep rose pink Deep rose pink
R. anthopogon
White Yellow Yellowish white Pink/Yellow Pinkish white Pinkish white
R. arboreum Vermillion/Deep red Red pink Crimson Crimson/Pink Blood red Red
R. baileyi Faded red / Purple - - Reddish purple Reddish purple Dark purple
R. barbatum Bright red Deep red Deep crimson Crimson/Scarlet Scarlet red Blood red
R. camelliiflorum White White - White tinged with pink White tinged with pink White
R. campanulatum Bright purple Purple Lilac White/Pink/Purplish blue Rosy purple Rosy purple
R. campylocarpum Yellow Yellow Pale sulphur Yellow/White Bright sulphur yellow Yellow
R. ciliatum White /Light pink White/Pale rosy - White/Rosy White to pink -
R. cinnabarinum Red Orange rose Scarlet Red/Orange/Yellow/Pink Cinnabar red -
R. dalhousiae White White Cream White/Chamois yellow White White
R. decipiens - - - - Rose pink -
R. edgeworthii Creamish - Pure white White/Pink White tinged pink -
R. falconeri Creamish purple White yellowish Cream ivory Yellow Pale yellow Pale yellow
R. fulgens Bright red Scarlet Crimson Scarlet Blood red Blood red
R. glaucophyllum Light red Dull rose - White/Pink/Rosy/Red Pinkish purple -
R. grande White White Pure white Ivory Creamy white Creamy white
R. griffithianum White White White White White White
R. hodgsonii Light red Bright rose Purplish Pink Rose pink -
R. lanatum Yellow Yellow - Pale Yellow Pale sulphur yellow -
R. lepidotum Yellow Yellow/Dull purple Red Yellow/Pink/Purple Deep yellow Deep yellow
R. lindleyi Light yellow - - - White tinged pink -
R. maddenii White White White White White flushed pink White
R. nivale Pinkish red Rose red - Magenta Lavender pink -
R. niveum Light yellow pink Lilac - Magenta Smoky blue Purple mauve
R. pendulum Pink - - White White White
R. pumilum Red Rose - Pink Rose pink -
R. setosum Red Red - Purplish red Reddish purple Reddish purple
R. smithii Bright deep red - - Pink - -
R. sikkimense - - - - Blood red Blood red
R. thomsonii Deep red Deep crimson Dark crimson Blood red Blood red Blood red
R. triflorum Yellow - - Pale Yellow Light yellow -
R. vaccinioides - White / Pinkish - - White tinged with pink White tinged pink
R. virgatum Purple Purple - Purple/Pink/White Purple rosy -
R. wallichii White / Pink - - Lilac Rose Pink -
R. wightii Yellow Yellow Yellow Yellow Yellow Yellow
* Philipson & Philipson (1975); Cullen (1980); Chamberlain (1982);        (-) = Species not found/data not recorded
Table 8(a): Flowering concentration of Sikkim Himalayan rhododendrons over the altitude and time period (month-wise).
Altitude Months
(m amsl) Feb. March April May June July Aug. Sep.
1500-2000 - 01 03 03 - - - -
2001-2500 - 02 05 05 01 - - -
2501-3000 - 03 05 08 05 01 - -
3001-3500 - 03 10 10 04 02 - -
3501-4000 - 02 08 07 07 02 - -
4001-4500 - - - 04 10 08 - -
4501-5000 - - - 03 05 04 - -
5001-5500 - - - - 01 02 03 -
5501-6000 - - - - - 01 02 -
Table 8(b): Fruiting concentration of Sikkim Himalayan rhododendrons over the altitude and time period (month-wise).
Altitude Months
(m amsl) Feb. March April May June July Aug. Sep.
1500-2000 - 02 02 03 - - - -
2001-2500 - 02 03 06 02 - - -
2501-3000 - 02 04 12 05 - - -
3001-3500 - 01 07 10 04 07 - -
3501-4000 - 01 05 08 10 02 - -
4001-4500 - - - 02 07 11 02 -
4501-5000 - - - - 03 05 04 -
5001-5500 - - - - 01 04 01 -
5501-6000 - - - - - 02 01 -
Table 9: Number of species along with altitudinal gradient in Sikkim Himalaya.
Altitude (m amsl) No. of Species
1500-2000 07
2001-2500 13
2501-3000 23
3001-3500 29
3501-4000 26
4001-4500 22
4501-5000 12
5001-5500 06
5501-6000 03

Species Availability: It was observed that the greatest frequency of species occurrence in the Sikkim Himalayan rhododendrons is found within the upper temperate belt (i.e., between 3000-3500m amsl). The altitudinal distribution is shown in Table 9. On a general observation, the species availability decreases drastically from 4500m upward and 2500m downwards. Species concentration increases with the latitudinal progression from south to north.
Vertical distribution: The 36 species of rhododendrons in the Sikkim Himalaya showed barrel shaped vertical distribution along with altitudinal gradient. R. arboreum is a common species that showed distribution from 1500m elevation to up to 4000m amsl, while other species of wide ecological amplitude ranging from 2500m up to 6000m amsl were R. anthopogon and R. setosum . Highest species occurrence was recorded between 3000 to 3500m amsl. Species vertical distribution is shown in Table 10. The ubiquitous species among the Sikkim Himalayan rhododendrons (which generally are not localized) are R. arboreum , R. barbatum and most of the epiphytes. Except a few species almost all of the rhododendrons of the region have a limit to its growing range.

Table 10: Vertical distribution of Sikkim Himalayan rhododendrons.
Altitude (m amsl) Species Distribution
1500-2000 R. arboreum, R. cinnabarinum, R. dalhousiae, R. edgeworthii, R. grande, R. griffithianum, R. lindleyi
2001-2500 R. arboreum, R. camelliiflorum, R. cinnabarinum, R. dalhousiae, R. edgeworthii, R. grande, R. griffithianum, R. lepidotum, R. lindleyi, R. maddenii, R. triflorum, R. vaccinioides, R. virgatum
2501-3000 R. anthopogon, R. arboreum, R. baileyi, R. barbatum, R. camelliiflorum, R. campanulatum, R. ciliatum, R. cinnabarinum, R. dalhousiae, R. edgeworthii, R. falconeri, R. glaucophyllum, R. grande, R. griffithianum, R. hodgsonii, R. lepidotum, R. leptocarpum, R. lindleyi, R. maddenii, R. setosum, R. triflorum, R. vaccinioides, R. virgatum
3001-3500 R. anthopogon, R. arboretum, R. bailey, R. barbate, R. camelliiflorum, R. campanulatum, R. campylocarpum R. ciliatum, R. cinnabarinum, R. decipiens, R. edgeworthii, R. falconeri, R. glaucophyllum, R. grande, R. griffithianum, R. hodgsonii, R. lepidotum, R. leptocarpum, R. lindleyi, R. maddenii, R. niveum, R. pendulum, R. pumilum, R. setosum, R. thomsonii R. triflorum, R. vaccinioides, R. virgatum, R. wightii
3501-4000 R. anthopogon, R. arboreum, R. baileyi, R. barbatum, R. camelliiflorum, R. campanulatum, R. campylocarpum R. ciliatum, R. cinnabarinum, R. decipiens, R. edgeworthii, R. falconeri, R. fulgens, R. glaucophyllum, R. hodgsonii, R. lanatum, R. lepidotum, R. maddenii, R. niveum, R. pendulum, R. pumilum, R. setosum, R. thomsonii R. sikkimense R. triflorum
4001- 4500 R. aeruginosum, R. anthopogon, R. baileyi, R. campanulatum, R. campylocarpum, R. ciliatum, R. cinnabarinum, R. decipiens, R. edgeworthii, R. fulgens, R. glaucophyllum, R. hodgsonii, R. lanatum, R. lepidotum, R. maddenii, R. niveum, R. pendulum, R. pumilum, R. thomsonii, R. setosum, R. wallichii, R. wightii
4501-5000 R. aeruginosum, R. anthopogon, R. baileyi, R. campanulatum, R. fulgens, R. lepidotum, R. nivale, R. pendulum, R. pumilum, R. setosum, R. thomsonii, R. wallichii, R. wightii
5001-5500 R. aeruginosum, R. anthopogon, R. campanulatum, R. fulgens, R. nivale, R. setosum
5501-6000 R. anthopogon, R. nivale, R. setosum

Horizontal distribution: Under observation, the species were found to be quite "site specific," or conversely, small locality or rather niche quality played important part in the species being found or not; small virtual "islands" of their niches sometimes overlap. Highly delicate ecosystem balancing mechanism must be operating in the area to support such diversity in form, habitat and the harmony. Horizontal distribution of rhododendrons are noted in the Singlila ridge, Lachung valley and Yuksam-Thangsing area.
Rarity of species: Status in Table 11 is drawn up as plant availability to space. The different intraspecific taxa are naturally rare. It was noted that the species which are perched high up on trees and precipices at different places enjoy a natural barrier (e.g., R. camelliiflorum , R. lindleyi , R. griffithianum , R. edgeworthii ). Disturbance to the host tree, however, may prove otherwise. Several species of rhododendrons are gradually becoming rare and endangered in their natural habit. In the Sikkim Himalaya out of 36 species 18 species are being considered as Threatened/Rare/Endangered species. The rest of the species are out of danger at present; however, these species are also in localized conditions and may be wiped out, if the proper measures could not be taken. Our study also reveals that while one species, namely R. leptocarpum (also known as R. micromeres ), has been almost totally exterminated in the area and probably extinct. Now 3 others are rare, 4 endangered, 2 vulnerable and 11 others are threatened.

Table 11: Rarity status of Sikkim Himalayan rhododendrons
Species Number Space Status
Few Extremely
Large Ubiquitous Localized Acutely
R. aeruginosum + + Threatened
R. anthopogon + + Threatened
R. arboreum + + Vulnerable
R. baileyi + + Threatened
R. barbatum + +
R. camelliiflorum + +
R. campanulatum + +
R. campylocarpum + +
R. ciliatum + + Threatened
R. cinnabarinum + +
R. dalhousiae + +
R. decipiens + + Threatened
R. edgeworthii + +
R. falconeri + + Threatened
R. fulgens + + Rare
R. glaucophyllum + +
R. grande + + Threatened
R. griffithianum + +
R. hodgsonii + +
R. lanatum + +
R. lepidotum + +
R. leptocarpum + + Endangered
R. lindleyi + +
R. maddenii + + Rare
R. nivale + + + Threatened
R. niveum + Endangered
R. pendulum + + Rare
R. pumilum + + Endangered
R. setosum + + Threatened
R. sikkimense + + Endangered
R. thomsonii + + Vulnerable
R. triflorum + + Threatened
R. vaccinioides + +
R. virgatum + +
R. wallichii + +
R. wightii + + Threatened

Rhododendron is one of the largest and most diverse genera in the plant kingdom, comprising approximately 1,000 species and coming from all over the globe. While some of the Himalayan species are 30m or more in height, leaves up to 0.3m long, there are also many dwarf species only a few inches tall with leaves just over 1/3 of an inch long. Although the greatest concentration of both type of species and individuals occurs throughout a region of the Himalayas comprising Tibet, Nepal, Bhutan, Sikkim, Burma, Arunachal Pradesh and the provinces of Sichuan and Yunnan in China, the distribution is nearly worldwide. Only South America and Africa are without any native species (Hooker, 1849-51; Leach, 1961).
The rhododendrons are most well known as a conspicuous element of Himalaya vegetation on the one hand and as an important and diverse group of ornamental plants on the other. Now we have about 85 taxa of indigenous rhododendrons to our knowledge in Indian flora (36 species in Sikkim Himalaya). The number of species of Sikkim Himalayan rhododendrons has been a constant source of problems to many workers. The actual reason is found to be the systematics itself for altering the total count. In the case of Hooker (1849-51) and Clarke (1875) the tally varies mostly because of classificatory approaches. Between these two and the work of Pradhan and Lachungpa (1990), the total does not agree which is mainly because within this big block of time some more taxa were added. The first record was 33. The second one coming just after some years of time slash down the number to 29. The last two are only 8 years apart and still differences show up. Between these two steps (19th and 20th century) the figures keep on jumping up and down. A few of the species can be easily traced as to their bearing, but some are very difficult.
Clarke, whose work on rhododendrons pulled up the total figure of the species to 29, worked almost entirely on the Hooker's material collected for the flora of British India (1875) though the work follows Hooker's own Rhododendrons of Sikkim Himalaya (1849). The total figure projection by Clarke has some element of suggestion that many of Hooker's species were summarily sidelined or clubbed with other species, which ultimately showed the final species in lesser number. The latest work of Pradhan and Lachungpa (1990) has the total of 36 species with a remarkable number of various subspecies and varieties and its focus gives a more or less complete picture. The varied climatic regime in the region and a good selection stock of the species are very much conducive for bringing out new species. The inbreeding in the wild has been pointed out by many workers, and several taxa (from R. triflorum and R. thomsonii ) are cited in the study, which may vie for a berth in species ranking. The Sikkimense rhododendron ( R. sikkimense ), R. salignum , R. dalhousiae var. tashii are the new ones from the region.
The time elapsed between the last collection and the latest ones is more than a century, which also points to the potentiality of finding new species within the region.
The rhododendrons are basically woody in nature and the rhododendrons of the region are not an exception. The trees are seldom straight in trunk and grow to a height of 20m. Contorted and twisted specimens are more frequent than rare. A shallow root system is noticed. Generally the trees are much branching and spreading, either when growing singly or inside community stand. Almost all the trees, given the right situation, tend to become gregarious. Among the shrubs R. thomsonii , R. companulatum , R. compylocarpum , R. glaucophyllum and R. lanatum are the community forming species. The brush/bushlet forms of rhododendrons are gregarious in nature and form expansive singly species communities. R. pendulum is sometimes found epiphytic. Epiphytic species are usually encountered on open, sunny slopes of not severe inclination. These show comparatively large leaves when encountered on open, sunny slopes in comparison to when observed in epiphytic condition. Epiphytic species are relatively fewer and most grow pendulous rather than upright. One upright growing example is R. vaccinioides , though later in life it is prone to become pendulous. It is observed that rhododendron habit usually changes from lower to higher attitude and the trend is higher the altitude smaller becomes the plant. This relative habit is also true age wise where equal age of plants is remarkably discernible in habit. On a general observation the Sikkim Himalayan rhododendron habit is the combined effect of temperature, humidity and wind rather than geology, pedology and landforms.
It was observed that most of the epiphytes belong to the lepidote group and the trees and tree-like species are mostly elepidote. Also noteworthy, the snow loving rhododendrons are lepidote.
Apart from the obvious un-matching of flower colours coming from different workers the variation of colours even within a single species was given at the Table 7. The general idea is that the darker climate produces lighter shades or vice-versa. The flower colours also may be attributed to different altitudinal effect. Although all of the rhododendrons of the region show a degree of difference in shade within species and though some are less marked ( R. campanulatum ), a few have drastic colour differences ( R. arboreum , R. thomsonii and R. cinnabarinum ). Pink and/or purple flowering species pose another problem in colour estimation because when the bloom gets older the shade becomes lighter. Thus, in R. decipiens to find purple and milky-white flowers on the same plant is usual but often faulty observation may be expected.
In a general sense, the rhododendrons are essentially terrestrial in nature. Under suitable environment the epiphytes are always found growing on soils, albeit the ground is a "raised earth." Generally, trees with longer life span and rough bark were found to be preferred as phorophytes (e.g., Quercus , Castanopsis , etc.). But this is not a general rule because it is seen that the epiphyte, conditions permitting, makes use of any available tree species that is found in the locality as epiphytes.
Some of the species grow also on rocks ( R. fulgens , R. lepidotum , R. pendulum , R. setosum , and R. camelliiflorum ) and to some extent R. anthopogon and R. baileyi . At favorable locations, it seems that almost all species take to the rocks as refuge.
Species that require shade to a varying degree are R. lanatum (under Abies species), R. fulgens , R. decipiens , R. wallichii , R. wightii and R. campanulatum (all under mixed community of dominant Abies species). All other species may be classified as "outdoors" because they grow quite well in the open.
Most of the brush/brushlets are found on open sloping terrain. The slopes offer somewhat well drained, and thus less moist, conditions where a few species make their home, e.g., R. virgatum , R. pendulum , etc. The epiphytes rhododendrons, which are found sometimes growing on soil, are generally restricted to sloping terrain where water logging is less experienced (as is the situation on a tree environment). Thus shrubs favour level grounds, the river-terraces being their favorite retreats.
The species that are trees or reaching a tree-like dimension are sometimes found as canopy members inside a forest stand; some still are found as dominating species occupying the upper story as is the case found at places like Tendong Peak ( R. grande ) and Hillay-Barshay ( R. falconeri ). Rhododendrons usually grow under a moist environment with plenty of soil moisture and humidity and at locations above 2800m spend about 3 months under snow. Winter with severe drops in temperature at localities above 2800m produces permafrost-type of situation in the soil. These plants at such localities thus always experience a physiological drought condition. To tend off such tundra-like conditions (for the snow and frozen groundwater are not available to the plants at such times) various modifications come up in the form of scales, hairs on the leaves and leaf curling. This also resulted in very slow growth of rhododendrons.
The species that experience and grow over regular snow-slide and avalanches are R. niveum and R. thomsonii . The response to sheer stress of snow slides has now made the R. thomsonii at Phuni to be growing in an inclined manner.
In conclusion, the habitat of both epiphytic as well as terrestrial rhododendrons requires consideration towards its preservation.
The Singalila ridge, once the magnificent abode of over 20 species (and some of them exclusive to the area) of rhododendrons, is now a dying floral mass. It is a regular route for the trekkers during the peak season for rhododendron flowering. Compounded with severe grazing and fuel wood collection the rhododendrons are now much less found. The Lachung valley is a highly delicate ecosystem balancing mechanism and must be operating in the area to support such diversity in form, habitat and harmony. The watershed of Lachung Chhu still has the scope to be studied in its totality unlike the Singalila ridge, which has lost a large part of its natural biota and virgin terrain. Small patches usually were found to be harboring a group of particular species; for example, in the Yakchay area R. niveum is localized. Here not a single plant of R. thomsonii is found whereas about 1km away (aerial distance) at Phuni these grow in impenetrable thickets. And here not a trace of R. niveum is found. The altitude difference is c 100m only. A little higher up between 3000-3700m amsl R. campanulatum grows luxuriantly up to Yumthang. Between these patches is found R. baileyi for a short stretch. Others are R. decipiens at Shingba (3200m), R. cinnabarinum (3500m), and small patches of R. wightii , R. setosum and R. grande . Interspersed between these are found the less gregarious ones, e.g., R. lanatum , R. pendulum , R. fulgens . A little up from Yumthang one can observe R. aeruginosum (scatteringly), R. campylocarpum (in swarms), etc. Yakchay proper is also the location of R. virgatum , R. triflorum facing southeast. Same is the case of R. lepidotum .
The Yuksam-Thangsing area remains one of the best preserve for Sikkim Himalayan rhododendrons. It is in this area that the first sighting of R. leptocarpum was made. Difficult terrain, absence of pliable road and the presence of intact natural habitat forest cover have contributed much in the stability of the environment and preservation of rhododendrons in the region. Most remarkable is the comparatively large size of the epiphytic rhododendron population.
Out of all the three major areas of rhododendron availability in the region the Yuksam-Thangsing area is comparatively least disturbed. Recently the area has been annexed to the Khangchendzonga National park.
Rhododendrons tend to thrive in Sikkim Himalaya with heavy rain and acidic soil. This centre of concentration lies in eastern Nepal, Sikkim and Bhutan. It has been observed that there is a conspicuous drop in the number of species from eastern to the western regions. Among all the 36 species R. arboreum and R. niveum have been attracting special attention since these species have been adopted as the National Flower of Nepal in 1962 and State Flower of Sikkim respectively (Pradhan and Lachungpa, 1990). In spite of much interest, several species of rhododendrons are gradually becoming rare and endangered in their natural habit. In India as many as 43 rhododendron species (including varieties) have been listed as Rare, Endangered or Threatened (Botanical survey of India). In the Sikkim Himalaya out of 36 species 18 species are being considered as Threatened/Rare/Endangered species. The rest of the species are out of danger at present; however, these species are also in localized conditions and may be wiped out, if the proper measures could not be taken. Local communities inhabiting the temperate and high attitude areas of Sikkim Himalaya traditionally use rhododendrons for fuel wood since this burns even under raw condition. Recently several developmental activities, particularly road construction, have adversely affected habitats of this specially valued and economically important species. Furthermore, shifting cultivation continues to be practiced which is being improved upon. Our study also reveals that while one species, namely R. leptoazrpum (also known as R . micromeres ), has been almost totally exterminated in the area and probably extinct, now 3 others are rare, 4 endangered, 2 vulnerable and 11 others are threatened.

Rhododendrons are the denizens of high altitude mainly inhabiting a vast section of southeastern Asia stretching from northwestern Himalaya through Nepal, Sikkim, eastern Tibet, Bhutan, Arunanchal Pradesh, Northern Burma and Western and central China. The genus forms a very important dominant combination of forest types in the cool temperate and subalpine region, and also on the alpine meadows of the Sikkim Himalaya. It supports a wide range of biodiversity. This genus may be regarded as a key-stone element in these high altitude areas. A large percentage of the Indian species are found in Sikkim. Therefore, Sikkim is the most appropriate location to undertake conservation studies of the rhododendrons in the India. Due to the human interference the natural populations of rhododendrons in the Sikkim Himalaya are gradually diminishing. The rhododendrons flowers have an enormous range of colors, shapes, and sizes in their wild forms. The horticultural values are well known. The rhododendrons are conducive to inter and intra generic crosses and therefore open to hybridization. Revolution on horticultural and biotechnological aspects of the genus is needed to fully convert the aesthetic of rhododendrons into commercial advantage. Taking consideration of all the above we have carried out detailed study on rhododendron status in Sikkim Himalaya. Extensive survey and assessment of different rhododendron habitats were made towards documentation of baseline information and study data were compared with the available data of previous workers. Summarily it may be concluded that the threat to almost all species of rhododendrons of Sikkim Himalaya is a eye opener towards anthropogenic pressure over rhododendrons and its consequence in the region. In a relative sense, it may be argued that more interference would bring about greater disturbance to the rhododendron species and its habitat. Regular population habitat viability and risk stimulation assessment should be generated on the basis of newly identified threats, population status and other relevant research. These studies can provide estimates for the survival of these populations, also indicating the various steps needed for improving the overall conservation status of rhododendron species. This would prove indispensable for saving many threatened and endangered species.

The authors want to acknowledge the support, concern and encouragements made by Mr. L.K. Rai, Dr. KK. Singh, GBPIHED, Gangtok, Sikkim; Dr. E. Sharma, ICIMOD, Nepal; Dr. L.M.S. Palni, Sr. Scientific Advisor (Biotechnology Programme), Government of Uttranchal; and Prof. R.N. Shukla, School of Environmental Biology, APSU, Rewa, during the course of this study.

Chamberlain, D.F. (1982). A revision of Rhododendrons, II subgenus Hymenanthes. Notes Roy. Bot. Garden, Edinburgh. 39: 2,1-480.
Clarke, C.B. (1875). J.D. Hooker Flora of British India. 3: 462-475.
Cowan, A. M. & Cowan, J.M. (1938). Trees of Northern Bengal . Calcutta.
Cullen, J. & Chamberlain, D.F. (1978). A Preliminary synopsis of the genus rhododendron. Notes Roy. Bot. Garden, Edinburgh. 56: 105-126.
Cullen, J. (1980). A Revision of Rhododendron 1. Subgenus Rhododendron Sections Rhododendron & Proganathum. Notes from the Royal Botanic Garden Edinburgh. Vol. 39, no.1.
Gamble, J. (1936). A Manual of Indian Timbers , London.
Hooker, J.D. (1851). Rhododendrons of Sikkim Himalaya. Tree . 19-21.
Hooker, J.D. (1849). Notes, chiefly botanical, made during an excursion from Darjeeling to Tonglu. J. Asia Society Bengal . 18(1) 419-446.
Hooker, J.D. (1949-51). The Rhododendron of the Sikkim Himalaya; being an account, botanical & geographical of the rhododendron recently discovered in the mountains of eastern Himalaya . Reeve, London.
Hooker, J.D. (1849). The Rhododendron of Sikkim Himalaya , London.
Justice, C. (2000). Sikkim 2000: The Ascent to Yumthang and the search for R. wightii . Journal of American Rhododendron Society 54: (3) 162-170.
Lacita, C.C. (1916). Plants collected in Sikkim, including the Kalimpong district. April 8 to May 9, 1913.
Lave & Smoerum, R.S. (2001) Sikkim 2000: The Danish rhododendron adventure. Journal of American Rhododendron Society . 55:(4) 193-194.
Leach, D.G. (1961). Rhododendron: of the World . Charles Scribners's Sons, New York.
Maiti, A. & Chauhan, A.S. (2000). Threatened plants in the Sikkim Himalaya. Hima. Paryavaran A Journal of EPA . 113-120.
Philipson, W.R. & Philipson, M.L. (1975). A Revision of Rhododendron 1. Section Lapponicum, notes from the Royal Botanic Garden, Edinburgh. Vol. 34: 1-72.
Pradhan, U.C. & Lachungpa M.L. (1990). Sikkim Himalayan Rhododendrons . Primulaceae Books, Kalimpong, West Bengal.
Pradhan, U.C. (1985). A preliminary enumeration of rhododendrons of the region Part I. Himalayan Plant Journal . 3 (8): 123.
Pradhan, U.C. (1986). A preliminary enumeration of rhododendrons of the region Part II. Himalayan Plant Journal . 4(lll2): 73-76.
Rehder (1978). Species Rhododendron. In Notes R.B.G. Edinb. 36(1): 113.
Starling, B.N. (1984). Among the giants and dwarfs of Sikkim. R.H.S. Rhododendrons 1984/85 with Magnolias and Camellias London. pp 1-8.