Comparative anatomy of some Rhododendron species of Arunachal Pradesh, India

The present study was carried out on ten Rhododendron species of different plant habits (shrub and tree) viz., R. dendricola, R. edgeworthii, R. keysii, R. maddennii, R. neriiflorum, R. virgatum, R. kendrickii, R. kesangiae, R. barbatum and R. sinogrande were selected from Tawang and West Kameng districts of Arunachal Pradesh with the objectives to evaluate anatomical characteristics and ecological adaptations of these species. Wood samples were taken from five randomly selected trees/shrubs for each species. Woods were ring-porous in R. kendrickii, R. neriiflorum and R. sinogrande; semi-ring porous in R. barbatum and diffuse-porous in remaining species. Vessels solitary, angular outline, tube-shaped with small tails, helical thickenings, scalariform perforation plate, tyloses present, opposite inter-vessel pits, vessel-ray pits with distinct borders similar to inter-vessel pits, fibres small, thin-walled, bordered pits, septate fibres, scanty paratracheal parenchyma, uniseriate, multiseriate rays with uniseriate wings, disjunctive ray parenchyma, homocellular and heterocellular rays were common anatomical features. However, variations in anatomical characters such as alternate inter-vessel pits in R. edgeworthii and R. kendrickii, occasional scalariform inter-vessel pits in R. neriiflorum and R. sinogrande, pith flecks in R. sinogrande and R. barbatum were observed. R. kendrickii has the maximum fibre percentage and parenchyma percentage was highest in R. kesangiae. All the selected species were xeromorphic and have combination of both primitive and advanced characters. Principal component analysis revealed close relationship between R. sinogrande and R. kesangiae; R. kendrickii, R. keysii and R. edgeworthii. Thus, anatomical characteristics can be used for identification of Rhododendron species.