Variation in Rhododendron arboreum Sm. complex (Ericaceae): insights from exomorphology, leaf anatomy and pollen morphology

Rhododendron arboreum Sm., placed under the genus Rhododendron L. in the family Ericaceae Juss. consists of c. 1000 species, of these c. 102 species occur in India. R. arboreum Sm. is restricted to a few South Eastern Asian countries. In India, the species is distributed in the Himalayas, North Eastern India and hill tops of South Western Ghats. Detailed investigations of the genus were studied by several workers but nobody studied variation in R. arboreum complex. A few workers described pollen morphology of Ericaceae including Rhododendron, but they did not study different subspecies of R. arboreum. No detailed investigation on leaf anatomy was also reported. The purpose of the present study is to evaluate the contribution of leaf anatomy and pollen morphology along with herbarium and field based exomorphological data to delimit infraspecific variations in R. arboreum complex.