Anatomical adaptations and mycorrhizal morphology of two threatened Eulophia (Orchidaceae) growing in southern Western Ghats, India
2021
Koshila Ravi, Ravichandran | Sowmiya, Srinivasan | Balachandar, Mayakrishnan | Muthukumar, Thangavelu
The vegetative anatomy of Eulophia spectabilis (Dennst.) Suresh and Eulophia pulchra (Thouars) Lindl., of subfamily Epidendroideae (Orchidaceae), of subtribe Eulophiinae was investigated to bring out the anatomical differences, mycorrhizal morphology and also their adaptation to thrive in stressful xerophytic habitats. Transverse sections of plant parts were freehand sectioned and stained with various staining solutions for anatomical investigation. Stomatal characteristics were examined by maceration technique. The leaves of both Eulophia species shared similar anatomical characteristics including tertracytic stomata on abaxial surface, uniseriate epidermis on both the surfaces, homogenous mesophyll comprising of intercellular spaces and collateral vascular bundles. Fibre bundles are present only in the leaves of E. pulchra. Likewise, the anatomy of leaf-sheath in both the species resembles those of the leaves except for the large air chambers. The pseudobulb of E. pulchra consists of parenchymatous ground tissue containing air chambers, raphides, starch grains, and water-storage cells and collateral vascular bundles. Starch grains are present only in the rhizomes of E. pulchra ground tissues. In roots, the velamen is undifferentiated in E. pulchra, but distinguished into epivelamen and endovelamen in E. spectabilis. Starch grains are present in root pith cells in E. pulchra. The cell dimensions of most plant parts varied significantly (P<0.05) among the Eulophia species. Contrarily there were no significant (P>0.05) differences in orchid mycorrhizal colonization between the Eulophia species. Thus, these ground orchids possessed several anatomical features that enable them to thrive in dry habitats.
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