Structural Adaptations of Bulbophyllum and Dendrobium (Orchidaceae) to the Epiphytic Habitat and Their Phylogenetic Implications

Abstract

The morpho-anatomical studies in Bulbophyllum and Dendrobium (Orchidaceae) with special reference to ecological adaptation and phylogenetic implications have been carried out. The vegetative parts were collected from different parts of North-East Himalaya and Western and Eastern Ghats of India. All were epiphytes belonging to tribe Dendrobieae. These plant parts were fixed in FAA (Formaline-Acetic acid-Alcohol) and usual methods of microtomy had followed. Stomata were confined to abaxial surface in all the investigated taxa. The presence of stomatal ledges and substomatal chambers is helpful in reducing leaf transpiration and evaporation of water. Absorbing trichomes were recorded only in Sikkim collections of D. anceps whereas they were absent in Darjeeling collections. In case of D. herbaceum and D. moschatum, these were present only in Kerala collections and absent in Karnataka collections. Single- or multi-layered velamen has been reported in both genera. It was observed that tilosomes were always associated with single layered velamen roots whereas completely absent in multilayered velamen taxa. Based on anatomical data, sectional delineation and phylogenetic interrelationships have been discussed.