Taxonomic significance of epidermal morphology in Nigerian Rhizophoraceae

Epidermal morphology of adaxial and abaxial leaf surfaces of five genera of the family Rhizophoraceae in Nigeria were studied by light microscopy. The epidermises are composed of variously shaped cells which, in surface view, range in outline from triangular, rectangular to more commonly hexagonal, polygonal and irregular. Cuticular striations are absent except in Poga oleosa in which conspicuous striae encircle the guard cells and run parallel to the axis of non-specialized epidermal cells. Anticlinal walls are either straight, curved or undulate. Leaves of all genera are hypostomatic. Paracytic stromata occur in Cassipourea and Anisophyllea while all species of Rhizophora possess cyclocytic stomata. The stomata of Anopyxis are of the anisocytic type and those of Poga anomocytic. The morphology of the guard cells and stomatal ledges varies significantly within the family. Evidence is produced to support the suspected hybrid nature of Rhizophora harrisonii. Other features of the epidermis that show variation include stomatal size, shape and density, size and density of epidermal cells, and cell wall thickness. Epidermal characters are of some utility in elucidating relationships and identifying some taxa within the family.