Palyno-anatomical diversity and its implication in the taxonomy of some Plantaginaceae species

The pollen and foliar epidermal morphological features are mostly used in resolving the taxonomic issue of flowering plant families. This study aimed to investigate, the comparative foliar epidermal anatomy and pollen features of Plantaginaceae through scanning electron microscopy (SEM) and light microscopy (LM) to evaluate its taxonomic significance. Pollen characteristics were measured from each specimen under LM. Details of the exine sculpture were also analyzed under SEM. Generally, the pollen grains are small to medium-sized, radially symmetrical, circular amb with the prolate shape of pollen grains in equatorial axis, tricolpate and pantoporate. The exine sculpture is reticulate, micro-reticulate, scabrate, verrucate, striate and rugulate. The genus Plantago shows diverse pollen morphology, with variations in shape, size, aperture type, and exine ornamentation across the species. Likewise, the genus Veronica has generally trizonocolpate pollen grains, with rare differences in aperture type and exine ornamentation. Foliar epidermal characters were observed using a light microscope and found variations in epidermal cell shape, pattern of anticlinal wall, type and shape of stomata, and types of trichomes. In addition, some quantitative characters were also studied and data were statistically analyzed such as epidermal cell size, stomatal size, stomatal pore size and stomatal index. The results indicated that the shape of the epidermal cell in most species was irregular, isodiametric and polygonal on both abaxial and adaxial surfaces. The anticlinal wall pattern was mostly undulate but some species have straight and smooth walls. Leaves were mostly amphistomatic while the type of stomata were found as anisocytic and anomocytic. Unicellular and multicellular non-glandular trichomes were also observed. Thus, foliar epidermal together with pollen morphological features strengthen and give additional support to the taxonomy of Plantaginaceae.