A botanical collection tour along the 100 Km. road track passing through, the Dafla hills and Apatanang valley and lying between Kimin (213 m.) and Ziro (1525 m) in the Subansiri F.D., undertaken during September 1959 yielded 383 species of angiosperms and 66 species of Pteridophytes amongst others. This paper presents the topography, climate and vegetation together with a comprehensive analysis of the floristic composition of the vegetational types and is followed by enumeration of the species in the appendix.
Vegetation in the Dafla hills area visited is ascribed to tropical evergreen forest from Kimin to Pitepool and to subtropical evergreen forest, and grassland formation between Kherbari and Hapoli, the last one representing a biotic climax.
Apatanang valley is a flat alluvial plain of about 20 sq. miles representing the bed of dried up lake and is very suitable for rice and millet cultivation. Pinus wallichiana and Dendrocalamus sikkimensis are extensively planted in the surrounding hillocks.
The analysis of the distribution data shows the occurrence of a large number of species in the area as common to neighbouring. region e.g. Assam sharing 260 species; Sikkim, 119 species; Western Himalayas, 107 species; Burma, 51 species; Manipur, 15 species; Bengal, 29 species; Bihar and Orissa, 13 species and Deccan Peninsula, 28 species.
Borreria ocymoides, Torenia asiatica and Cyanotis papilionacea, so far reported as restricted to Deccan Peninsula, Impatiens porrecta, I. paludosa and Solanum khasianum, as enemic to Khasia hills, Argyreia wallichii as endemic to Sikkim, Exacum tetragonum var. stylosa and Dendrobium chrysotoxum reported by Hooker from Burma have now been collected from Subansiri F.D.