Leaf epidermal micromorphology of Zingiber (Zingiberaceae) from China and its systematic significance

Leaf epidermal characteristics are important for phylogenetic and taxonomic studies of many plants, but there is currently insufficient such data for this application in Zingiber species. Therefore, the leaf epidermal micromorphology of 22 species in three sections of Zingiber was investigated by light microscopy and scanning electron microscopy. Differences between various taxonomic groups of Zingiberaceae were also compared to assess their phylogenetic and taxonomic significance. As in other genera of Zingiberaceae, the epidermal cells in both the adaxial and abaxial epidermis of Zingiber species were found to be hexagonal or polygonal, with non-sinuous anticlinal walls that are arranged parallel to leaf veins. Tetracytic stomata are mostly randomly distributed in the intercostal regions of both surfaces and are more common on the abaxial surface. The stomatal density of the species in sect. Pleuranthesis is significantly lower than that in sects. Zingiber and Cryptanthium. There are two types of trichome in Zingiber: so-called "delicate" trichomes are present in most species, while "stout" trichomes with a swollen base are only found in Z. corallinum and Z. montanum. Oil cells occur in both epidermal layers of some species in sects. Zingiber and Cryptanthium, but only in the abaxial epidermis of Z. ellipticum in sect. Pleuranthesis. Crystals are found in the abaxial epidermis only in all species, but are present in both epidermal layers of Z. corallinum and Z. montanum. Although the epidermal morphology is similar in most Zingiber species, stomatal density, type of trichome and distribution of oil cells and crystals offer valuable information for the systematic and taxonomic studies in this genus.