Micromorphological variability of leaf epidermis in Mesoamerican common bean ( Phaseolus vulgaris , Leguminosae)

The purpose of this work was to make a detailed description of leaf epidermal characteristics among four Mesoamerican common bean ( Phaseolus vulgaris L.) types, since they may play a role in plant defence against pathogens and/or drought. Therefore, we studied variability of epidermal cell number per mm2, stomatal size and number per mm2, stomatal index, and trichome density and dimensions on both the adaxial and abaxial epidermal surfaces. In all the common bean types studied, both surfaces of the leaves were devoid of wax crystalloids. Trichome density and distribution differed among the common bean types. Furthermore, the abaxial leaf surface always presented more trichomes than the adaxial surface. The leaves were amphistomatic, with the guard cells located in line with epidermal cells. Common bean leaves presented paracytic, anomocytic and anisocytic stomatal types. All common beans presented the adaxial epidermis of the leaves with a lower density of bigger stomates than on the abaxial epidermis. Our results demonstrate that micromorphological characteristics on both leaf surfaces are variable traits among common bean types.