Leaf epidermis of the African genus Mallotus Lour. (Euphorbiaceae) section Rottleropsis Müll. Arg. and its systematic value

ABSTRACT The leaf epidermal information on the two African Mallotus species is updated with data derived from herbarium specimens using light and scanning electron microscopy. Stomata, indumentum and cuticular ornamentation are particularly informative. All the species have paracytic stomatal type and amphistomatic leaves with stomata on the adaxial surface being restricted to the midribs and big veins. Brachyparacytic stomatal type and abaxially restricted disc-shaped multicellular glandular trichomes distinguish M. oppositifolius var. glabratus from M. oppositifolius var. pubescens, while presence of hemibrachyparacytic stomata and cuticular striations differentiate M. subulatus from M. oppositifolius. However, the quantitative and leaf areole characters overlap considerably. Based on a suite of these characters, the distant relationship indicated between M. oppositifolius and M. subulatus and the suggestion to subsume section Axenfeldia in the polyphyletic section Rottleropsis is upheld with some cross-referenced data; also, an indented dichotomous key for separating the three taxa is presented.