Comparative study on root anatomy of six species of Himalayan Dendrobium Swartz

Comprehensive knowledge of plant anatomy is an absolute necessity for accurately identifying taxa during their vegetative phase. Orchidaceae family has been extensively studied in the Himalayan region, with a focus on morphology and floristics. However, the anatomy of orchid roots has not been investigated in detail. This study examines the root anatomy of six Himalayan Dendrobium species (D. chrysanthum, D. densiflorum, D. longicornu, D. nobile, D. rotundatum, and D. transparens) using standard plant anatomy techniques. Qualitative and quantitative traits were observed and analysed, including the multi-layered velamen, stele and cortical tissue area, and number of xylem strands, which are distinct characteristics of genus Dendrobium. ANOVA and Tukey's test at 5% significance level were used to quantitatively examine cross-sections of the roots and identify significant differences. All six studied taxa possess velamen tissues with cells having spirally thickened walls, and a single-layered exodermis with cells of varying sizes. The cortex was multi-layered and contained parenchymatous water-storage cells, while a uniseriate endodermis with passage cells were observed. D. chrysanthum and D. rotundatum had xylem and phloem elements embedded in parenchymatous tissues, whereas D. densiflorum, D. longicornu, D. nobile, and D. transparens had xylem and phloem elements embedded in sclerenchymatous tissues. Cell sizes in different root tissues varied significantly. A dichotomous key based on the root anatomical traits for the identification of these Dendrobium species is provided. Future research is suggested to explore additional parameters and to conduct experiments to understand its anatomical response to epiphytism.