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14 WINTER 2008
Debjyoti Bhattacharyya* and M.
Sanjappa
Botanical Survey of India, CGO Complex,
3rd MSO Building, Block F, 5th
Floor, DF Block, Sector I, Salt Lake
City, Kolkata 700 064. West Bengal.
India.
Abstract
e genus Rhododendron L. (Ericaceae)
is represented by about 80 species in India.
It is distributed mainly in different regions
and altitudes of Himalayas with a greater
concentration in the eastern Himalayas.
In this paper, the habitat and ecological
aspects of rhododendrons in India are
presented with particular emphasis on
different physical factors. e influences
of anthropogenic as well as catastrophic
activities, which cause serious depletion of
rhododendrons in their natural habitats,
are also discussed.
Keywords: Rhododendron, India, habitat,
physical factors, threats.
____
Rhododendrons are among the most
popular flowering plants that adorn the
mountains with fantastic and ineffable
flowers of different shades. e rich
variety of rhododendron foliage can equal
the delights of their blooms, especially
the young shoots. Some species are also
very charming for their attractive fragrant
flowers.
It is the largest genus of the family
Ericaceae as well as among one of the largest
flowering plant genera in Asia (Cullen
and Chamberlain, 1978). Globally, the
genus is represented by about 1025 species
(Chamberlain et al., 1996).
e genus is mostly concentrated
in the temperate regions of northern
hemisphere especially in Sino-Himalayas
(Eastern Himalayas and Western China).
Besides this main center,
rhododendrons are further extended
towards southern China as well as to
northeastern China and Japan. About 571
species are found in China (Mingyuan et
al., 2005). A good number are also found in
Myanmar, ailand, Malaysia, Indonesia,
Philippines and New Guinea. 155 species
are endemic in New Guinea (perhaps
a secondary center of distribution).
A few species are also reported from
Afghanistan, Pakistan, southern Europe
and northern America. Two species are
reported from Australia. e most striking
fact is that there are no rhododendrons
in Africa, central and southern America
(Hutchinson, 1947). In India, there are
about 80 species with 10 subspecies and
14 varieties (Bhattacharyya, 2005).
Distribution in India
Rhododendrons of India are widely
distributed in different regions and
altitudes mainly in the Himalayas
(Figure 1). Of the four parallel ranges in
Himalayas, rhododendrons are practically
absent in the Siwaliks, a few are found in
the lesser Himalayas and majority of them
are in the greater Himalayas. Only one
species occurs in Trans-Himalayan region
located in extreme north-west of India
(including the cold deserts of Jammu and
Kashmir and Himachal Pradesh). e
greater Himalayas are thus an ideal locality
for rhododendrons in India. Besides this, a
good number of species are found in north-
eastern India particularly in Naga and
Khasi hills. One subspecies nilagiricum of
Rhododendron arboreum occurs in Western
Ghats.
State-wise, Arunachal Pradesh
harbours the maximum number of
species (67 species) followed by Sikkim
(36 species). 19 species are recognized
from Darjeeling district of West Bengal, 7
from Nagaland, 5 from Manipur, 2 from
Mizoram and Meghalaya each, 6 species
from Uttaranchal and 4 from Himachal
Pradesh and Jammu & Kashmir each.
Only one subspecies is found in Tamil
Nadu and Kerala (Figure 2).
Habitat
e habitat of the genus Rhododendron
ranges from subtropical and temperate
to subalpine and alpine ecosystems. In
India, maximum species diversity (48
species) is recorded from the temperate
and subalpine regions of the Himalayas
between 3000-3500 m (Figure 3). Most
rhododendrons are found in high rainfall,
humid temperate regions of highly organic
well-drained acidic soils and reach their
magnificent development in the high hills
and mountains that have dry, cool summer
and rainy seasons (Milleville, 2002).
Mosses and lichens are commonly
found in association with Rhododendron
species. e epilithic/epiphytic rhododen-
drons grow on the moss-wrapped rocks
and tree trunks associated with Agapetes,
Vaccinium and orchids. Eight species are
found growing epilithically/epiphytically,
which are confined to eastern Himalayas
and north-east India. Such species are
entirely absent in western Himalayas.
Most of the arboreal species are found
in mixed broad-leaved forests in subtropical
regions, sometimes form the dominant
canopy of pure ericaceous forests (Figure
4a) along with Gaultheria. Shrubby
species grow in temperate forests (between
2700-2900 m) and in subalpine regions
(between 2900-3500 m) in association
with Abies, Tsuga, Betula, etc. In western
Himalayas and in eastern Arunachal
Pradesh (Lohit district), rhododendrons
are found associated with chir pine (Pinus
roxburghii). Alpine rhododendron scrubs
(Figure 4b) are found above 3500 m and
Rhododendron Habitats in India
JOURNAL AMERICAN RHODODENDRON SOCIETY 15
Figure 1. Map showing distribution of Rhododendrons in
India.
(Map source – National Atlas and Thematic Mapping Organi-
sation, Department of Science & Technology, Government of
India, Kolkata – 700 064; Map outline drawn from India-Phys-
iography, Plate 2).
Figure 2. Species richness of Rhododendrons in different
states in India.
Figure 3. Species richness of Rhododendrons in different al-
titudes in India.
are dominant between 4200-4600 m.
Rhododendron nivale occurs above 5000
m, sometimes near glacier. Many species
are cultivated in the gardens of subtropical
areas.
Factors Responsible for Supporting
Rhododendrons
Soil
Rhododendrons, in general, grow in
well-drained acidic soils, which are rich
in organic matter and low in elements.
Most species grow on slopes where there
is no water logging. Some species like
R. hodgsonii, R. falconeri, etc., are found
in swampy soils and they usually leave
behind fibrous remnants of old leaves on
the ground. Epilithic/epiphytic species
grow either on heavily moist mossy rocks
or pendulous from cliffs (Figure 4c) or tree
trunks. Alpine species like R. anthopogon,
R. lepidotum, R. setosum and R. nivale grow
in soil with limited water and nutrients. In
alpine pastures, all these species are buried
under snow during winter, and when the
snow melts in summer, the soil is exposed
for a period of 3-4 months and the plants
start sprouting (Figure 4d) and flowering.
e soil of the temperate regions are
exposed a little earlier to that of subalpine
and alpine areas and the sprouting starts
at lower elevation and gradually proceeds
upward. e soil of the subtropical
regions of the Himalayas and Western
Ghats remains free from snow, where R.
arboreum grows.
Humidity and Rainfall
According to Indian meteorological
tables (1931-1990), the North-East India
experiences high rainfall (240-1142 cm
per annum) because of its proximity to
Bay of Bengal and direct exposures to
the South-West Monsoon. e Eastern
Himalayas receive 200-500 cm annual
rainfall. It gradually decreases towards
west and becomes minimum (11-75 cm
per annum) in the Trans-Himalayas. e
16 WINTER 2008
Eastern Himalayas receive as much as 100-
200 cm more precipitation per annum
than the Western Himalayas. Annual
average rainfall of one of the collection
localities (Darjeeling district) of different
species of Rhododendron is c. 285 cm. Six
species occur in western Himalayas, where
annual average rainfall is c. 195 cm. e
species like R. anthopogon, R. lepidotum
grow in higher elevations of Jammu and
Kashmir and Himachal Pradesh, where
annual average rainfall is c. 34 mm. R.
nivale occurs at an elevation of more
than 5000 m, where the habitat is totally
dry with incessant cold rain or sleet in
summer. As the weather is very dry in
their habitat, there is an adaptation to
check the transpiration rates by reducing
the leaf surface area. On the other hand,
maximum number of species occurs in
the moist region like north-eastern India.
R. arboreum subsp. nilagiricum grows in
moist areas of Western Ghats particularly
in Ooty, Kodaikanal (Tamil Nadu) and
Munnar (Kerala). In the moist region, tree
species are abundant which form mixed
or pure Rhododendron forest (Figure 4e).
Some species survive in both the moist
and partly dry conditions.
Light
e alpine meadows above 3000 m are
relatively shiny compared to subtropical
Himalayas. e rhododendrons in these
areas have dwarf, stunted habit (Figure 4f).
Duration of light period in Himalayas is
severely affected between 1500-3000 m
due to formation of fog and clouds during
flowering season of rhododendrons (late
March-May). Different rhododendrons in
cloud-affected areas include many broad-
leaved species like R falconeri, R. grande, R.
hodgsonii, R. sinogrande, etc. Some other
species found in association with these
broad-leaved species are R. barbatum, R.
campylocarpum, R. thomsonii, etc., which
are characterized by relatively smaller
leaves. Species occurring in the foggy/
cloudy area (below 3000 m) show broader
and longer leaves than those occurring
above 3000 m.
Exposed hills in north and north-
east are the places of luxuriant growth of
rhododendrons. Flower colour sometimes
may vary with different slopes on which
they grow. Generally, plants with darker
shades of flowers grown in sun-exposed
slopes become pale and faded when grown
in the shade.
Temperature
e effect of temperature on the growth
and flowering of different species of
Rhododendron is directly related as
observed during the course of this study.
A plant of R. arboreum subsp. arboreum
var. arboreum from Lachung (altitude ca
3000 m; temperature recorded was 8°C-
12°C during day, 1°C-3°C during night
in the month of April), North Sikkim
was introduced in the nursery of Indian
Botanic Garden (IBG), Howrah (sea
level) grew to c. 10 cm in 5 years where
the average temperature ranges from 25°-
33°C. Another plant of R. falconeri from
Varsey Rhododendron Sanctuary (2900
m, temperature recorded was 12°C-
15°C during day, 1°C-5°C during night
in the month of April) West Sikkim was
introduced in the Garden of Sikkim
Himalayan Circle (ca 1800 m, average
temperature ranges from 15°C-23°C),
Botanical Survey of India, Gangtak
whose growth rate was also very slow. In
contrast, the other species like R. formosum
(introduced from Elephant falls, upper
Shillong, 1960 m, temperature recorded
during day 12°C-15°C during late March)
is somewhat heat tolerant which flowered
in the gardens of Eastern Circle, Botanical
Survey of India, Shillong (1550 m) where
the average day temperature recorded at
the beginning of April was 19°C-21°C.
R. griffithianum also flowers in slightly
warmer conditions in comparison to other
species.
In alpine zones, the dwarf
rhododendrons remain dormant under
snow during winter seasons to overcome
unfavourable cold period. ough, no
snow is observed in alpine meadows
during flowering seasons (particularly
July) of these species, the temperature
is much less (near 0°C at night). e
alpine rhododendrons adapt themselves
physiologically to withstand the cold
conditions throughout the year. Cox
(1990) reported that the curling of leaves
in cold weather is a natural mechanism,
not only to reduce water loss but also to
shed snow.
Altitude
e habit of the Rhododendron species
is directly related to the altitude of
their habitat. Any tall tree species of
comparatively lower elevations may get
dwarfed when exposed to unfavourable
conditions in higher elevations. Altitude
coupled with other factors like light and
temperature is supposed to be responsible
for the growth patterns of different species.
Cox (1990) stated that high elevations
and wind can make species dwarf, which
normally attain much larger proportions
in lower, more sheltered positions. Species
growing in higher altitudes often have
thicker indumentum than those occurring
in the lower elevations. Moreover, the
thickness of the indumentum sometimes
also varies within the same species growing
in different altitudes. Further, J. D.
Hooker (1854) showed that the duration
between flowering and seed ripening
is directly related to the altitude of the
habitat of a particular species. Generally,
plants at higher elevation take less time for
seed ripening than those at lower altitudes.
According to Kingdon-Ward (1934), the
alternate wetting, drying and freezing day
after day in frosted environment may be
responsible for earlier maturity of seeds.
Slope
Slope is also an important factor,
which has direct bearing on diversity
of species. Some species like R.
falconeri, R. grande, R. hodgsonii, R.
maddenii (when terricolous), R niveum,
etc., prefer to grow in flat ground (Figure
4g) whereas others (R. formosum, R.
johnstoneanum, etc.) like growing in ravines
and on slopes (Figure 4h). is factor is
directly related to the water content of the
soil. As most species prefer well-drained
soils, thus they are slope loving. Maximum
JOURNAL AMERICAN RHODODENDRON SOCIETY 17
species occurs in south facing slopes due to
availability of light and moisture.
Atmospheric Pressure and Velocity of Wind
In alpine zones, low atmospheric pressure
and high velocity of wind cause desiccation
of Rhododendron species, which in turn
modify their growth-form into dwarf
shrubs with stunted or prostrate woody
branches.
Optimal Requirement for Growth and
Flowering of Species
It can be concluded that in general the
physical factors discussed above coupled
with other biological factors have influential
role on the growth pattern and flowering
of different species of Rhododendron. Well-
drained, well-aerated, acidic soil rich in
humus and low in elements, high rainfall,
humid atmosphere, low temperature,
high elevations and sunexposed slopes
are optimal for luxuriant growth of
rhododendrons. Any imbalance in the
ecological factors may cause deterioration
of rhododendron habitat in high
altitudes.
Species Rarity due to Habitat
Destruction
With the diminishing of green cover
almost everywhere, rhododendrons are
also experiencing the impact of disturbed
habitats. Herbarium study and field
observations reveal that many species are
gradually becoming rare. For instance,
entire populations of R. niveum have
almost disappeared and only one patch
of few plants could be traced in the
Yumthang valley, Sikkim during present
study. R. edgeworthii once collected from
Sinchul Lake area, Darjeeling is hardly seen
now. R. vaccinioides could not be located
from the place of its earlier collection in
Fambanghlo Wildlife Sanctuary, Sikkim.
Population coverage of many species like
R. baileyi, R. dalhousieae var. rhabdotum,
R. nuttallii, R. pumilum, etc., are not
considered common species. Rarity
of 14 species is evident from its poor
representation in herbaria. R. maddenii
has also become very rare in its earlier
reported locality (Choongtam) and is now
represented by 1 or 2 plants in isolated
localities along the bank of Lachung Chu
river. Specimens of 7 species were not
found in any Indian herbaria visited during
this study nor could they be collected from
known localities of their earlier collection.
us, out of 80 species in India, 21 can
be considered as rare. However, current
exploration to Arunachal is bringing more
new information regarding the species
richness of the area.
Some of the major causes for rarity of
different species of rhododendrons may
be the changes in climatic conditions of
alpine, subalpine and temperate habitats,
retreating of glaciers, natural disasters like
major landslides and earthquakes. Habitat
destruction due to anthropogenic activities
like logging for firing in construction
of roads (in Tawang and Yumthang),
disposal of waste by tourists and trekkers,
over grazing and over exploitation of
plants for fodder and other purposes are
great potential threats. Jhum cultivation
(shifting cultivation) practiced particularly
in Arunachal Pradesh and Nagaland is
also a major threat for disappearance of
low-altitude species like R. arboreum.
During present study, Saramati mountain
peak, Nagaland (floristically similar to
Japoo hills, which is the Type locality
of many species of Rhododendron) was
visited which is one of the richest areas for
endemic species R. macabeanum. ough
the area was declared as Wildlife Sanctuary
(Fakim WL Sanctuary) but the people
of the nearest village (anamir) totally
depend upon this dominant tree species
of Rhododendron for firewood, which
may cause adverse effect on the entire
population of this species. Leaves and
twigs of R. anthopogon are burnt as dhupi
(incense) in monasteries and temples in
Sikkim, Darjeeling district of West Bengal
and western Arunachal Pradesh (Tawang).
is may lead to large-scale depletion of its
natural population.
Conservation - A Prerequisite
To safeguard the habitats of
rhododendrons from further extinction,
in situ conservation is inevitable. However,
several measures have been taken to protect
the natural habitats of rhododendrons.
e Government has declared many spots
as protected areas in Sikkim (Tiwari and
Chauhan, 2006). Several NGOs are also
engaged in protecting the natural habitat
particularly in Yaksam, West Sikkim. Ex
situ conservation of rhododendrons in
India have also been initiated by G. B.
Pant Institute of Himalayan Environment
and Development at its arboretum near
Pangthang, Sikkim at c. 1800 m altitude
where 24 species are grown (Singh et al.,
2003). Moreover, any effort to check
global warming may secure Rhododendron
habitats from further deterioration.
Acknowledgements
e first author (DB) is thankful to the
Director, Botanical Survey of India for
help and encouragement and for awarding
a Research Fellowship. anks are also
due to the Principal Chief Conservator
of Forest of all the States and Divisional
Forest Officers of all the Protected Areas
visited during the study for issuing research
permit and to forest guards and porters for
their assistance and help during field trips.
References
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G. Argent, G. Fairweather, and K. S.
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Rhododendron species. London: B. T.
Batsford Ltd.
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Rhododendron. Notes Roy. Bot. Gard.
Edinburgh 36:105-126.
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Distribution of Rhododendrons. e
18 WINTER 2008
Rhododendron Year Book 1947: 87-98. e
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7. Kingdon-Ward, F. 1934. A Plant
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*Present address: Institute of Environ-
mental Studies and Wetland Management,
B-4, LA Block, Sector III, Salt Lake City,
Kolkata 700 098. West Bengal. India.
E-mail: dbhatt26@rediffmail.com
Figure 4. Different habitats of rhododendrons. a, Varsey Rhododendron Sanctuary,
West Sikkim, 2900 m – pure broad-leaved rhododendron forest; b, Above Dzongri, West
Sikkim, 4200 m – alpine scrubs dominated by R. anthopogon; c, On way to Chhangu,
East Sikkim, 3100 m – epilithic R. camelliiorum hanging from moist cliffs; d, Katao,
North Sikkim, 4100 m – R. lepidotum adapted to survive in snow; e, Above Bikebhanjan,
Darjeeling district, West Bengal, 3100 m – dense population of R. arboreum; f, Sela,
Tawang district, Arunachal Pradesh, 4200 m – alpine zone dominated by dwarf, stunted
R. lepidotum (i) and R. anthopogon (ii); g, Valley of Lachung Chu, Choongtam, North
Sikkim, 1830 m – R. maddenii in at river bank; h, On way to Elephant falls, above
Shillong, Meghalaya, 1800 m – scattered population of R. formosum in association with
Pinus.
