Foregoing discussion helps us to conclude that the Indian flora are heterogeneous and can be grouped under a number of floristic regions.
The whole credit of highlighting the regional characteristics of the country’s natural vegetation goes to Hooker and Thomson in 1855. Later on C.B. Clarke (1898) divided this part of Asia into 6 floristic regions: (1) Himalayan region-(a) Eastern Himalaya, and (b) Western Himalaya, (2) Arid region, (3) Malabar region, (4) Coromandel region, (5)Gangaplain, and (6) Assam region. In 1907 J.D. Hooker identified 8 floristic regions in the British India. These include (1) Eastern Himalaya, (2) Western Himalaya, (3) Indus plain, (4) Ganga plain, (5) Malabar region, (6) Deccan region, (7) Maldive and Sri Lanka, and (8) Burma (not in India).
In 1937 C.C. Calder identified 6 floristic regions in the country: (1) North-western Himalaya, (2) Eastern Himalaya, (3) Indus Plain, (4) Ganga Plain, (5) Deccan region, and (6) Malabar region.
D. Chatterji (1939), on the basis of certain indigenous plant species in different parts of the country, divided India into 8 main floristic regions.
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1. Eastern Himalaya
This region includes the hilly areas of West Bengal, Sikkim, and Arunachal Pradesh which is characterised by heavy rainfall, low snow fall, high temperature and humidity. This area of undulating topography nurtures about 4,000 species of plants which vary from tropical to temperate and Alpine with increasing altitude. Among the sub-tropical forests extending from Tarai plains to a height of 1524 m sal, oak, chestnut are the main trees. Between 1524 m and 3657 m temperate broad leafed trees like Quercus lamellosa Smith, Quercus Lineata Bl., Quercus pachyphylla Kurz, Castanopsis, Magnolia, Pyrus and Symplous Meliosmia dominate. Between 743 m and 3657 m lies a belt of conical forest with trees like Abies Webbiana, Picea Symplocos, Eurya etc. Beyond 3657 m of height lies a zone of Alpine forests with main trees like silver, fir, juniper, pine, birch and rhododendrons.
2. Western Himalaya
This region covering Uttaranchal, Himachal Pradesh, Jammu and Kashmir enjoys less rainfall and temperature than its eastern counterpart but the snow fall is heavier. Here again sub-tropical (up to 1524 m), temperate (1524 m to 3657 m) and Alpine (3657 m to 4572 m) vegetation types are noticed with the increasing height along the hill slopes. In submontane region up to the height of Sal, semul and Savanna type of vegetation are observed. Amongst temperate vegetation chirr, oak, deodar, alder, birch and conifers are important. Similarly Alpine vegetation between the altitude zones of 3657 to 4572 m is dominated by juniper, silver, fir, birch etc.
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3. Assam Region
This region includes the whole of the northeast including Assam, Meghalaya, Nagaland, Manipur, Tripura and Mizoram. Here vegetation depicts south-east Asian impact which maintains the Himalayan heterogeneity except the Alpine vegetation. The region is rich in various types of bamboos, and palms with Nilgiri type of grasslands at higher altitudes.
4. Ganga Plain
Being a distinct physiographic unit of country the region has typical floristic character tics of its own. The vegetation type ranges between semi-arid shrubs (the Aravalli region) to evergreen mangroves (the Ganga delta). Although due to de population and growing agricultural and economy” activities natural vegetation of the region has aim been wiped out but historical evidences sup dense vegetal cover with rich wild life. Sal and Aij (Terminalia tomentosa and Terminalia belerica) the representative species of the primordial vegetation.
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The vegetation of Uttar Pradesh belongs to deciduous type which changes to moist deciduous type in eastern Bihar and West Bengal and torn grove type in the Ganga delta. Besides, there different types of grasses all over the region deepening upon the local physical conditions.
5.Indus Plain
This floristic region incorporates plains Haryana, Punjab Rajasthan (west of the Aravallis Kachchh and northern parts of Gujarat. In this reign of scanty rainfall (less than 75 cm annually) though” shrubs and trees with thick bark predominate. Important trees include acacias, euphorbias, cacti, will palms (phoenix sylvestris), Khejra, Kanju and Pal etc. During rains short grasses also spring up.
6. Deccan Region
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This region covers major part of the Peninsii lar India. Here camamus vininalies and camam rotary are the main species of palms. Areas charac terised by granites and gneisses support teak, tend sal trees while semi-arid tracts contain thorny shrub Anderson (1863) and Mukerji (1935) through the’ respective studies in Parasnath and Mahendrag hills have tried to find out similarity between t vegetation of this region and the Himalayas.
7. Malabar Region
This region stretches all along the wasted coast from Gulf of Cambay to Cape Camorin. Here vegetation type ranges from moist tropical evergreen to broad leaf mixed and monsoon deciduous type. The Nilgiri hills show temperate forests. The region also contains ‘several species of plants with Malay origin.
8. Andaman-Nicobar Region
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The vegetation of this region has been greatly influenced by the Malayan and Burmese impact. It is of mainly tropical evergreen type with different varieties of palms, canes etc.
In Lakshadweep islands the vegetation is dominated by different varieties of shrubs and coconut trees.