Epidermal micromorphology of 17 species of Hemiboea (Gesneriaceae)

Leaf epidermal micromorphology was examined in 17 species of Hemiboea Clarke using scanning electron microscopy (SEM) to assess variation among taxonomic groups and evaluate the phylogenetic and taxonomic utility of epidermal traits. Results showed that the upper epidermal cells were predominantly hexagonal or polygonal, with nearly straight anticlinal walls, providing additional characters for intrageneric classification. The surface ornamentation of upper epidermal cells presents diverse morphological features, including linear wrinkles, smooth or glossy surfaces, granular textures, smooth protuberances, wrinkled protuberances, smooth linear textures, linear protuberances, linear textures, as well as the presence or absence of trichomes. The structure of lower epidermal cells was indistinct. Annular stomata exclusively occurred on the abaxial epidermis, displaying elliptic, narrowly elliptic, narrowly fusiform and subcircular morphologies. Guard cells were all kidney-shaped, with striations on the cuticle surface. Stomatal density ranged from 67 per mm² to 285 per mm². Trichome types included villous, pubescent, and puberulent. Seven key traits were selected for R-type cluster analysis and correlation analysis, which divided the 17 species of this genus into four groups. The results showed that morphological traits of the leaf epidermis, such as anticlinal wall pattern, cell ornamentation, and adaxial and abaxial trichome coverage, can serve as reliable criteria for species delimitation in Hemiboea. In contrast, stomatal density, stomatal area, and stomatal length-width ratio are unstable traits and should not be used as primary diagnostic characters for classification of species in this genus.