Comparative Taxonomic Studies of Two Species of Phaulopsis (Acanthaceae)

Phaulopsis grandiflora Mankt. and Phaulopsis imbricata (Forssk.) Sweet (Acanthaceae) are morphologically similar species whose taxonomic delimitation has often been problematic. This study provides a comparative analysis of their morphology, foliar anatomy, and palynology to identify reliable diagnostic characters. Morphological observations revealed differences in plant stature, leaf base, and corolla coloration, with trichomes occurring only in P. grandiflora. Anatomical investigations showed marked interspecific variation in stomatal size and frequency, guard cell dimensions, trichome presence, and epidermal cell structure. P. grandiflora exhibited larger stomata and guard cells, fewer but longer epidermal cells, and conspicuous trichomes. Conversely, P. imbricata displayed a higher stomatal index, denser epidermal cells with thicker walls, and absence of trichomes. Palynological results further distinguished the two species: P. grandiflora produced smaller, tricolporate pollen with a reticulate exine, whereas P. imbricata produced larger, heterocolporate pollen with striate-reticulate sculpturing and thicker exine walls. These pollen characters, less prone to environmental variation, provide strong and stable markers for species identification. The combined evidence confirms the distinct taxonomic identities of P. grandiflora and P. imbricata and demonstrates the value of integrating foliar anatomical and palynological data with morphology in systematic studies of Acanthaceae. Future molecular analyses are recommended to complement these findings and refine the phylogenetic placement of Phaulopsis within the family.