Comparative anatomy ofSirhookera (Orchidaceae) growing in Western Ghats of southern India

We compared the anatomical characteristics of vegetative organs, peduncle and mycorrhizal morphology of the two known species ofSirhookera(Epidendroideae, Orchidaceae) to identify anatomical markers for identification and the ecological adaptations of these species. The leaves are hypostomatic bearing tetracytic stomata and the walls of subsidiary cells are smooth inSirhookera lanceolataand undulate inSirhookera latifolia. On the adaxial and abaxial surfaces the leaves are covered by a thick cuticle. The hypodermis is dimorphic and present on both sides of the leaf; chlorenchyma is homogenous and the vascular bundles are collateral. The rhizome ofSirhookerapossesses a single-layered epidermis, thick cuticle, thin-walled parenchymatous ground tissue containing starch grains and scattered collateral vascular bundles. A thick-walled sclerenchymatous band separates the cortex from the parenchymatous ground tissue comprising of banded cells in the peduncle. Starch grains are present in the ground tissue of theS. latifoliapeduncle. The roots consist of the velamen, boolean AND-thickened exodermis, thin-walled cortex consisting of water-storage cells, O-thickened endodermis and a vascular cylinder with parenchymatous pith. Starch grains are present in the root cortical cells ofS. lanceolatabut absent inS. latifolia. Fungal pelotons that aids in nutrient acquisition were observed in the root cortical region of both species. The study revealed significant differences between the anatomical characteristics of the two species and that most of the anatomical features ofSirhookerarelate to their ecological adaptations.