Sikkim the 22^nd state of the Indian union, is a tiny land locked mountainous state in the Eastern Himalayas. It is bounded by Tibet on the North, Nepal on the West and Bhutan on the east. West Bengal state makes boundary on its south. The southern most part of Tibetan plateau butts right into Sikkim in the north giving a peculiar phyto-geographical region of Trans-Himalayan Character. Donghela the highest range which runs east to west in the northernmost part checks the monsoon rain to reach in the plateau region. Thus the Trans-Himalayan zone of the Sikkim has floral and faunal composition like of Tibet. Recently a considerable number of Tibetan plants have been reported from these areas. The two great parallel north-south running ranges; Chola in the east and Singalila range in the west have clearly demarcated Sikkim from Bhutan in the east and Nepal in the west. As we move towards south, the great river Teesta in the east and the Rangit in the west which runs from north to south gave rise to third high median ridge culminating at meanam peak in the south.

Usually, valley is narrow at the top and broader as we reach towards the base but in Sikkim it is quite the reverse; broad valleys are at to top and narrow valleys at the base. This entire peculiar geographical feature helps Sikkim to become a biodiversity hot spot. It is estimated that we have more than 4000 flowering plants and about 300 ferns including 9 tree ferns. These are about 150 species of mammals, 500 species of birds, almost 700 species of butterflies and about 44 different species of fishes on riverine system. Sikkim boasts of having several hundred different kinds of orchid and has been known as Botanist's paradise. Though we have official record of 450 species orchids yet when careful survey was carried on the humid sub-tropical, temperate and alpine forest many new species of orchids were discovered differing from one valley to the other. Now the total species of orchid in Sikkim is slightly over 460 species. There are still virgin unexplored hills and valleys, which if explored the number of species may go beyond 500.

In its natural habitat orchid of Sikkim grows right from the base of hills up to 5000 metres. In higher elevation the orchid remain dormant almost about 6 months under the snow cover and blooms during summer in myriad of colours forming thick carpet. It blooms veiling the rugged terrain.

The most beautiful and very rare plants of the Alpine zone are Cypripedium tibeticum, C. himalicum and C. elegance. But due to their specific habitat requirement they are very rare and threatened.

The hills and vales provide a multitude of microclimate where one may come across dry cold of of Tibetan plateau to the dray heat of sub-tropical region. The orchid habitat met with are thus of varying kinds and are enumerated in accordance with the zone in which they occur. 

Alpine and sub-alpine zone: 2500-3000m.
This region is characterised by open grassy meadows, exposed rock surfaces and scrubby vegetation. Light intensity is higher; the subject is exposed to more ultraviolet rays. Precipitation is the form of snow, snow flashes coupled with low temperature below freezing during winter months. Orchid here has short life cycle. Here three major habitats can be recognised on these zones.

1. Open grassy meadow:
   It is normally a grazing ground of sleep and wild animals but in supports the growth of orchids like Orchis, Habenaria, Hermimium and Satyrium.

2. Rocky banks and moraine:
   Orchid like Orchis puberula King & Pantl. Grows on wet rocky places. Didiciea cunninghamii King & Pantl. And Cypripedium himalicum Rolfe. Have also been reported growing on moraine.

3. Under Betula - Conifer and Rhododendron - Juniper scrub & association.
   Species like Epipactis, Cephalanthera and Cypripedium thrive under such condition. Tipularia josephii Rchb. f. grown undershed of Betula and requires sandy soil.
   

Temperate and sub-temperate zone 1850-3500 m.
It is characterised by the presence of fog and mist almostthroughout the year. The treelike Picea, Laryx, tsuga, magnolia, Quercus and Rhododendron are common. Four manor habitats are found on this region.

1. Woods: the species like Goodyera secundiflora griff.g. reports R. Br. Zeuxine pumila, Calanthe spp etc. prefers humid shady forest floor.

2. Rocks: the species like Pleione humilis, (Sm) D. Don; Spathoglottis ixioides Lindl; Corybas himalaicha (King & Pantl.) prefers rocky slopes.

3. Both rocks and trees: the species like Cymbidium hookeranum Rchb. F. C. devonianum, C. longifolium D. Don; Coelogyne cristata Lindl; C. ochracea; C. corymbosa Lindl; Pleione hookerana (Lindl.); Dendrobium hookeranum Lindl; grows both on rocks and tree.

4. Grassy slopes: species like Habenaria, Herminium, Liparis, Satyrium grow in such slopes.

Sub-tropical zone 850-1250 m.
The region is characterised by heavy summer precipitation and day temperature of 25degrees Centigrade, which drop down to 20 degrees centigrade at night. Winter is usually cool, during dry and sunny. Mixed forests characterise this region, many of which are excellent host for orchid spps.

Five habitats can be found in this region.

1. Decaying vegetable debris is the forest floor
   Here the jewel orchids like Anoectochilus brevilabris lindl; A lanceolatus (Benth.) King. & Pantling; the entire saprophytic orchids like Epipogium, Grastrodia and Galeola spp etc. are found.

2. Palm and Bamboo (thicket)
   Many of Calanthe, Phaius and Eulophia etc. prefer this sort of habitat.

3. Cliff faces of dolomite or limestone
   Orchids like Paphiopedilum venustum and Paphiopedilum fairieanum prefers such habitat.

4. Mixed forest trees and secondary scrub vegetation
   Orchids like Dendrobium, Bulbophyllum, Ceologyne, Arachnis, Cymbidium, Gastrochillus and Kingidium prefer such habitat.

5. Mud Banks

The orchids like Anthogonia gracile wall. ex Lindl; Malaxis, Habenaria and Platanthera opts such kind of habitat.

Tropical zone 250-850 m.
Dense warm and humid tropical jungle prevails in this region. The humidity in monsoon may rise to a much as 100% the day temperature in summer may range from 30-35 degrees centigrade with cooler nights while in the winters it may range from 20-25 degrees centigrade.

1. Secondary shrub vegetation and rocks
   Orchids like Phalaenopsis, Dendrobium and Bulbophyllum grows on such habitat.

2. Tree
   All Dendrobium, Sarcanthus, Aerides, Vanda, Ascocenthum etc. prefer trees as their home.

3. Shady banks
   The orchids like Goodyera, Anrectochillus love this kind of habitat.

4. On sandstone rocks and muddy bank
   The orchids like Dipolomeris hirsuta, Arundina graminifolia prefer this kind of habitat.

Endemic species of orchids of Sikkim
1. Oberonia micranthus King. & Pantl. Tendong
2. Malaxis saprophyllum (King. & Pantl.) Tang & Wang
3. Liparis dongchenii (S. Z. Lucksom)
4. Calanthe trulliformis (King. & Pantl.)
5. C. alpina (Hook. f.)
6. C. Whiteana (King. & Pantl.)
7. C. chloroleuca (Lindl.)
8. C. anganii (S. Z. Lucksom)
9. C. keshabii (S. Z. Lucksom)
10. C. yuksomensis (S. Z. Lucksom)
11. Risleya atro - purpurea (King. & Pantl.)
12. Dediciea cunninghamii (King. & Pantl.)
13. Cymbidium whiteae (King. & Pantl.)
14. Taeniophyllum retro - apiculatum (King. & Pantl.)
15. T. crepidiforme (King. & Pantl.)
16. Thrixpermum pygmaeum (King. & Pantl.)
17. Uncifera lancifolia (King & Pantl.)
18. Biermannia bimaculata (King. & Pantl.)
19. Gastrochillus affinis (King. & Pantl.)
20. Venda pumila (Hook. f.)