The Eastern Himalayan vegetation is characterised by an abundance of rhododendrons and orchids, ferns, bryophytes, lichens besides tree like Terminalia, oaks, laurel, bamboos, hedychiums, etc. in the Eastern Himalayan region, orchidaceae, type flowering plant is the single largest family with as many as 600 species representing more than 50% of total taxa known from India. Hundreds of species of Asteraceae, Poaceae, Leguninoceae, Roseceae, Scorphulariaceae, Rubiaceae, Euphorbiaceae, Cyperaceae and Saxifragaceae represent 10 dominant families of angiosperms in the area. About 40% of total Himalayan flora is endemic with the majority occurring in the eastern flank. Of the gymnosperns, 15 species occur in Eastern Himalayas with at least 5 genera being confined to the region. Of the ptendophytes (fern and fern allies), 70% of polypodiaceous taxa of India are concentrated in Eastern Himalaya .
Nearly 50% of more than 2000 moss species are known from the region. Of the liverworts, more than 320 species are known from the region with a high percentage of endermism. At least 728 taxa out of 2000 species known from this country occur in the Eastern Himalaya .
The Eastern Himalayan region is also well-known for medicinal and aromatic plants of the genera Aconitum, Asparagus, Berberis, Loscorea, Ephedra, Gentlna, Hedychurum, Inula, Prunus, Rheum, Rosa, Saussurea, etc. 82 species of crop plants of Eastern Himalaya is also well documented. Due to increasing loss of habitat and impact of human activites, a large number of species are becoming vulnerable or threatened.
The richness of floral diversity could be appreciated from the point that West Bengal occupying only 2.7% of total area of India possesses more than 12% of floral diversity in angiosperm (flowering plants) in the area outside Dooars and Darjeeling Himalaya. The southern deltaic parts of West Bengal represent a distinctive floristic combination of 70 species in the Sunderban Mangrove ecosystem. Of these, 35 species are considered true mangroves, 28 as mangrove associates and seven species as obligate mangrove. Such a combination outnumbers the taxa in other mangrove ecosystems of India .
To summarise it can be said that, in the north, which includes the outer Himalayas , the forest zone begins with the Alpine/Sub-Alpine meadows and Rhododendron forests with Junipers at its highest attitudinal situation.
Below this level, occur the temperate forests of Oaks, Chestnuts, Laurels, Magnolia, Alder, Birch, Bucklandia etc, along with Tsuga in patches. In the lowest slopes and continuing into the plains of Dooars and Terai tropical and subtropical mixed forests, ranging from moist deciduous to semi-evergreen and moist Sal forests are found. The sub-Himalayan tract is crisscrossed by a large number of rivers and streams and in the flood plains of these rivers rivarian forests with Khair, Sisso etc. occur along with an alluvial Savannah woodland formation. Further south, in the lower alluvial plains of the Ganga and Mahananda in the districts of Malda, North and South Dinajpur , fresh water swamp forests of Barringtonia accutangala are seen. At the southern extremities, the estuaries of the Ganga system bear the tidal mangrove forests of Cenbps, Excoecarea, flhuophora, Avicennia Bruguiera, Lumnitzera, Xylocarpa, Heritiera and many other species with Nypa- palm brakes and Phoenix thickets in places. The south-western part of the State, which largely is an extension of the Chottanagpur plateau, has the Dry peninsular Sal Forests.