Leaf epidermic characters of Dendrobium (Orchidaceae) and its taxonomic significance

Leaf epidermis of 28 species representing 6 sections of Dendrobium were examined under light microscope(LM).The characters of leaf epidermis under LM are as follows: In Sect.Chrysotoxae Kraenzl.,Sect.Dendrobium,Sect.Stuposa Kraenzl.,Sect.Formosae Hook.f.and Sect.Stachyobium Lindl.,the stomata are only found in lower epidermis and in Sect.Aporum Lindl.also in upper epidermis.The shapes of upper and lower epidermal cells of these plants are irregular and the pattern of anticlinal walls are rather straight.Trichomes were found on both surfaces of the leaves of all examined species.The results indicate that the shapes of upper and lower epidermal cells,pattern of anticlinal walls and stomatal type and density are very similar to each other within the genus,which can not be regarded as useful evidence for infrageneric classification,and others such as stomatal size and shape,and trichome morphology and density are steadier characters and which be used to distinguish between sections and species.