Pollen Morphology as a Diagnostic Tool for Delimitation of Curcuma decipiens and Curcuma inodora: Two Allied Endemic Species from Peninsular India

Abstract

The genus Curcuma comprises numerous morphologically allied species whose delimitation is frequently complicated by overlapping vegetative characters and intraspecific variability. Among these, Curcuma decipiens and Curcuma inodora have long posed taxonomic challenges owing to partial morphological convergence and historical suggestions of synonymy. The present study employs an integrative palynological approach to resolve species boundaries between these two endemic taxa from Peninsular India. Pollen grains were extracted using standard acetolysis, examined under scanning electron microscopy (SEM), and quantitatively assessed for polar axis, equatorial diameter, P/E ratio, and detailed exine micromorphological traits. Statistical analyses, including descriptive morphometry, Morphometric Species Delimitation (MSD), Gaussian Mixture Modelling (GMM), and morphospace discontinuity assessment, were applied to evaluate interspecific differentiation. The results reveal pronounced quantitative divergence, with C. inodora exhibiting pollen grains more than 40% larger in both polar and equatorial dimensions than C. decipiens. Qualitative exine characters provide further diagnostic resolution, as C. inodora displays coarse regulate-reticulate sculpturing with high muri and deep lumina, whereas C. decipiens shows fine, shallow rugulation with low muri and reduced lumina development. Both GMM and MSD analyses consistently place the two taxa in distinct, non-overlapping morphospaces, confirming species-level separation. Collectively, the integrative palynological evidence robustly supports the recognition of C. decipiens and C. inodora as distinct biological species.