Systematic significance of morphology and leaf epidermal ultrastructure among Nigerian species of <i>Combretum loefl. (Combretaceae)</i>

A comparative study of morphological and foliar epidermal characters of sixteen species of Combretum in Nigeria was undertaken with light and scanning electron microscopy (SEM) to explore the variations and relationships among the members of Combretum for species identification and classification. The vegetative and reproductive features of 16 Combretum species were collected from various locations across Nigeria. Combretum had ovate, elliptic, oblong-elliptic, obovate and lanceolate leaves, 4-5 winged fruits, actinomorphic and hermaphrodite flowers. All Combretum species possessed amphistomatic and hypostomatic leaves. Systematically, the leaf epidermal ultrastructure revealed remarkable variation. All species had epidermal irregular cells with wavy anticlinal walls on both leaf surfaces, except for C. dolichopetalum and C. hispidum, which had polygonal cells with sinuate walls on adaxial and abaxial surfaces. Papillate epidermal cells were constantly observed in abaxial surface of C. binderanum, C. glutinosum and C. hypopilinum. Nonglandular trichomes (NGT) were predominant in all species, except C. nigricans. Considerable variation was recorded in trichome length. The shortest trichome was obtained on the adaxial surface in C. ghasalense (148.36±6.27 μm), whereas the longest trichome was recorded for C. constrictum (894.55±35.16 μm) on the same surface. The shape of the leaves, habit, number of stamens and fruit-wings, inflorescence position, presence or absence of caducous bracts, multicellular glands, epidermal cell shape and anticlinal walls are useful characters for the identification of some Combretum species. Based on these unique features of Combretum species, two groups and four sub-groups were identified with hierarchical cluster analysis.