Quantitative measures of leaf epidermal cells as a taxonomic and phylogenetic tool for the identification of Stanhopea species (Orchidaceae)

Orchids of the genus Stanhopea are currently identified only by their floral structure characteristics. A statistical analysis of a sig- nificant number of species of this genus disclosed that measurements of adaxial and abaxial epidermal cell surface areas can be correlated with spe- cific recognized species by a leaf printing method. This allows an objective- ly either positive or nearly positive confirmation of the identity of a species in the absence of flowers and without damage to plants. When ordering the mean values obtained for these surface areas in each species in a decreas- ing order, a correlation was observed in a hierarchical way that went from primitive to more advanced floral forms. This reflects the evolutionary radi- ation of the genus. It is established that in Stanhopea, the presence of large leaf epidermal cells on species from South America represents a primitive evolutionary condition that became to smaller cells in evolutionarily more recent individuals as the genus radiated towards Mexico.