THE INDIAN DENDROBIUMS

 
There are many dendrobiums native of India which are very popular. Species such as Dend. nobile are found in almost every collection of orchid plants. It can be of assistance to understanding the culture of these plants if some information is avail- able regarding their native habitats, and the following notes, hopefully, will be of help in this connection.


Articles in books and magazines often give an indication of a plants natural habitat 'by a geographical reference, or by indicating an altitudinal range over which it grows, and both these indications will be discussed. A knowledge of both can often allow more specific cultural information to be ascertained for a particular plant.


The genus dendrobium is an extensive one, from widely variable habitats. The Indian region contains many of the most popular plants of this genus, hence it is worth looking at the regional characteristics in some detail.


A. GEOGRAPHICAL HABITAT DESCRIPTION


Dr S.K. Bhattacharjee recently discussed the major Indian habitats. He noted that .the dendrobiums from there grow chiefly in trees in the jungle forests at various heights. Generally the Indian dendrobiums normally receive, and require under cultivation, heat and humidity during the plants active phase of growth, with then moderate exposure to air and light to mature the growths. This is followed by a cooler and decidedly drier period of rest during the winter months.


The main dendrobium habitats are as follows:


1. Assam, Khasia Hills, Mahipur, Naga Hills and Chadar contain the largest collection of dendrobium species including aggregatum, amoenum, caviniferum, chrysanthum, crepidatum, densiflorum, devonianum, falconeri, formosum, gibsonii, longicornu, pumilum, thrysiflorum (now densiflorum var. albo-luteum), wardianum and williamsoni.


The climate here is tropical monsoonal, with generally heavy rainfall from 2,000 mm (80 inches) to over 10,000 mm (400 inches) on the southern slopes of the Khasia Hills. Most rainfall falls during our equivalent December to March, the dry season ranging from our mid-April to the end of August. During most of the year it is stated atmospheric humidity is near saturation point. The mean temperature ranges from 17 oC (62 oF) in our July to 29 oC (84 oF) in our January.


2. Sikkim, Himalaya and Darjeeling comprises another important zone, a predominately rnountainous area, with Nepal to the west and Assam, Himalayas to the east, drained by the Tista River. The individual habitats here are distinguished by the altitude of the specific area discussed in part 2. Dendrobiums from this zone are chrysanthum, , callosum, densiflorum, farmers, gibsonii, hookerianum, longicornu. nobile (at the lowest altitudes -- 1,000 to 1,700 metres above sea level), primulinum, thrysiflorum (densiflorum var. albo-luteum) and transparens.


3. Many dendrobiums come from the plains of West Bengal and the hilly regions of Behar and Orissa. This region is hot and humid, being subject to tropical Monsoons. Annual rainfall rises from 2,000 mm to 3 000 mm on the Himalayan foothills. The summer temperatures can reach 45 - 50 oC, with a mean of 18 oC in winter (our July in the Southern Hemisphere) to 29 oC in our November. In Behar, at Ghota Nagpur, altitude runs from 700 to 1,700 metres in elevation, with an annual rainfall of 1,500 mm. The Orissa Hills are 500 to 1,000 metres high, with a rainfall of 1,000 to 1,500 mm.
Dendrobiums crepidatum, fimbriatum, formosum and nutans are found here.


4. The Kumoan Hills of the Manital, Almora, Garwal and Tehri districts lie at an elevation of 1,000 to 2,000 metres, Dendrobiums fimbriatum and primulinum coming from here.


5. Central and Southern India provide the home of many species. The Konkan area involves the coastal plain in West Bombay, receiving an annual rainfall of over 2,500 mm, with over seven dry months. Kanawa, south of Bombay, on the west edge of the Deccan Plateau, which covers most of peninsular India, contains many dendrobiums. Malabar, on the West Coast, receives a rainfall of 2,000 to 3,000 mm during our January to March, this increasing to 5,000 mm on the mountain slopes. The dry period extends for three months only. The Nilgiri Hills, south of the Deccan Plateau, averages 2,200 metres in height, rising to 2,700 metres. This extensive area holds Dendrobiums aphyllum and crepidatum.


6. Some dendrobiums are also found on some of the islands in the eastern Bay of Bengal - the Andaman and Nicabar Islands for example. The islands are mostly of hilly terrain, rising to some 800 metres. The climate is also tropical monsoonal, receiving a mean temperature of 29 oC, with a total rainfall of 2,250 to 3,250 mm, most of which falls during our equivalent December to March.

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B. ALTITUDINAL HABITAT ZONES


Pradahan, in his books, describes the main Indian vegetation zones as follows:

i) The alpine/sub-alpine zone from 3,500 to 5,000 m ASL No dendrobiums are found here.


ii) The temperate/sub-tropical zone from 1,850 - 3,500 m ASL This zone is characterised by the presence of fog and mists at almost all times of the year. Light intensity is high during the winter months. Dendrobiums listed here are candidum, clavatum, hookerianum, longicornu, and nutans.


Snow exists for 3 to 6 months of the year. Summer temperatures rarely exceed 20 oC above 2,850 metres. At the lower reaches, summer temperatures are between 18 20 oC, with humidity usually around 80 to 100 percent. Winter days can be 10 to 12 oC or less, with humidity failing to 60 80 percent.


iii) The sub-tropical zone running from 850 - 1,850 m ASL
A zone containing many dendrobiums. The climate is characterised by heavy summer precipitation. Day temperatures are 25 - 30 oC, falling to 20 0oC at night. Winters are cool (to 10 oC), dry and sunny, precipitation being from dews at night and in the early mornings.


The following dendrobium species are found growing in the mixed forest trees and secondary scrub vegetation -ancepts, chrysanthum, chrysotoxum, clavatum, crepidatum, densiforum, devonianum, fimbriatum, hookerianum, longicornu, nobile, parishii, primulinum, thrysiflorum (densiflorum var. albo-luteum), wardianum and williamsoni.


iv) The tropical zone from 250 - 850 m ASL
A number of dendrobiums make their home in the dense, warm and humid jungles which oCcur throughout this region. The humidity during the monsoon may rise to 100 percent. Day temperatures during summer range from 30 - 35 oC, with cooler nights. Winter day temperatures are 20 - 25 oC, the nights failing to 18 oC.
Many of the naturally epiphytic dendrobiums are found on roots or secondary scrub vegetation close to rivers. Aggregatum, amoenum, ancepts, aphyllum, chrysanthum, farmers, formosum, jenkinsii, pierardii and moschatum are found here.


v. The plains from sea level to 250 m ASL


Only those plains with a rainfall of over 2,000 mm contain forests suitable for orchid habitation. Dendrobium formosum and farmers are found here. Summer temperatures often exceed 40 oC, with rainfall less than that which falls on the surrounding hills.


APPENDIX
It may be of additional assistance if the altitudes given for the main growing areas of the species is listed. This information, and the geographic data, may be read together to ascertain a picture of the plants natural habitat.

Species

Altitude m. ASL

D. adduncum 500 - 800
D. aggregatum 250 - 800
D. amoenum 500 - 1300
D. ancepts 300 - 600
D. aphyllum 200 - 1000
D .aqueum 1000- 2000
D. bellatulum 1000- 2000
D. bicameratun 1500- 2000
D. bulboflorum 1000 - 2000
D. candidum 1000- 2300
D. catheartii 600 - 800
D. chrysanthum 800 -2000
D. chrysotoxum 400 - 1500
D. clavatum 1000 - 2000
D. crepidatum - 1200
D. crystallinum 1000 - 1700
D. cumulatum 300 - 1000
D. densiflorum 800 - 1500
D. denudans 1000 - 1700
D. devonianum 700 - 1700
D. eviaeflorum 1000 - 2000
D. falconer 1200 - 1500
D. farmeri 300 - 1000
D. fimbriatum 100 - 1500
D. fuscescens 1700 - 2300
D. gibsoni 700 - 1700
D. graminifolium 700 - 1700
D. herbaceum 700 - 1300
D. heteroCarpum 100 - 1300
D. heyniarum 1600 - 1600
D. hookerianum 1000- 2000
D. infundibulum 1500 - 1800
D. lituiflorum 1700 - 1800
D. longicornu 1200- 2500
D. macraei 1300 - 2700
D. machastachyum up to 2300
D. nobile 1000 - 1700
D. nutans 800 - 2000
D. ochriatum 1300 - 1500
D. ovatum 500 - 1700
D. parishii 1500 - 1800
D. pauciflorum 600 - 1300
D. piguanum 300 - 400
D. pierardii 1000
D. poryphyroChilum 1700 - 2300
D. primulinum 1000
D. pulchclum 1500 -2200
D. pygmaeum 400
D. ramosum 1300 - 1700
D. ruckeri 1300 1700
D. stuposum 400 1000
D. suicalum 1000
D. terminate 300 700
D. thrysiflorum 1500
D. transparens 1000 1500
D. wardianum 1500
D. williamsoni 1200 1500

I hope that these notes will be of assistance to those growing these popular Dendro- biums from this part of the world, especially as regards the temperature requirements.


REFERENCES


Dr 5.K. Bhattacharjee, 1976, "India: Major Dendrobium Habitat of the World", American Orchid SoCiety Bulletin, August, 1976, pp. 713-722.
Pradhan, Udai C., 1976, Indian Orchids: Guide to Identification and Culture - Volume l, 1979 Volume ll.

First published June 1985


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