Morpho-anatomy and mycorrhiza of epiphytic orchids of Tripura, Northeast India

In the present study, eight epiphytic orchids were collected from three different districts of Tripura to investigate the morphological and anatomical attributes of leaves and roots, as well as mycorrhizal morphology and colonization. The observations revealed that leaf morphological traits varied among the orchids. Additionally, root length and root collar diameter showed significant variation among the epiphytic orchids. Four types of stomata viz., anomocytic, tetracytic, diacytic and paracytic were observed. The stomatal index ranged from 14.89 in Dendrobium lindleyi Steud to 32.27 in Rhynchostylis retusa (L.)Blume. The maximum root length was observed in Acampe praemorsa (Roxb.) Blatt. & McCann, while minimum root length was noted in Dendrobium aphyllum (Roxb.)C.E.C.Fisch.. Dendrobium transparens Wall. ex Lindl. exhibited the highest root hair density, whereas R. retusa had the lowest. All the species examined showed mycorrhizal colonization percentages ranging from 36.77 in D. lindleyi to 71.66 in A. praemorsa. The percentage of root length with intact pelotons ranged from 12.91% in D. lindleyi to 42.41% in A. praemorsa, while the percentage with lysed pelotons ranged from 23.86% in D. lindleyi to 37.55% in D. aphyllum. The cortical cells of the epiphytic orchids contained both intact and lysed pelotons, with their ratio varying among the studied species. The morphological and anatomical characteristics, along with their mycorrhizal colonization patterns, firmly support the adaptive features of orchids as epiphytes.