The varied forest types of eastern Himalaya exhibit an enormous floristic diversity.   Apart from large number of timber species, there are innumerable varieties and kinds of orchids, medicinal plants, ferns, bamboos, canes, wild relative of large number of our cultivated plants, and even plants of biological curiosi ties, such as  parasites, saprophytes, etc. are found.  Other important group of plants are Rhododendrons, Hedychiums and oaks etc. Orchids form a dominant group of plants with their attractive and unique blooms. There are more than 600 species of orchids, 52 species of rhododendron, 18 species of hedychium, 16 species of oak,  18 species of canes, 45 species of bamboo in addition to large number of medicinal and aromatic plants.  Arunachal Pradesh has many species of endangered, endemic, primitive, and relict flora, Magnolia Pterocarpa pterocarpa is one such primitive angiosperm, which occurs in the foot-hills. Some rare and endangered flora that occur in Arunachal Pradesh are: Amentotazus assamica in Lohit District . Rhododendron arunachalense found in Subansiri District, Rhododendron dalhousie, and Tetracentron sinense, occurring in Kameng District, Rhododendron santapaul recorded in Subansiri  District.Gomphogyne macrocarpa found in Tirap and Kameng Districts, Gymnocladus assamicus and Lithocarpus Kamengensis available in Kameng district. Rhynchoglossum lasulinum in kameng and Subansiri District. Dendrocalamus sahni in Subansiri District. Hypericum griffitthii in Kameng District, Coptis teeta of Dibang Valley Districts, etc.

The State harbours about 52 species of of Rhododendrons, 18 species of Hedychium , 16 species of Qaks, 33 species of Coniters and a large number of fems and lichens.

About 500 species of orchids occur in Arunachal Pradesh. These include about 140 species of terrestrial orchids with 15 saprophytes and about 340 epiphytes found in the different forest types. The prominent species are:  Cymbidium ansifolium , C, grandiflorum, Coelogyne corymbosa. Dendroblum aphylla, D. fimbriatum var occulatum, D. densiflorum, Calanthe masuca, Phaius flavus, Paphiopedilum. Tairriearum, venustum renanthera imschootiana, vanda coenulea , etc. Rhynchostylis refusa is the state flower of Arunachal pradesh.

The vegetation of Arunachal Pradesh falls under four broad climatic categories and can be classified in five broad forest types with a sixth type of secondary forests. These are tropical forests, sub-tropical forests, pine forests, temperate forests and alpine forests.