Physiognomy, narrowly defined, refers to the general external appearance of vegetation based on growth form (gross morphology) of the dominant plants. Structure relates to the spacing and height of plants forming the matrix of the vegetation cover (Fosberg 1961). Often physiognomy is used to encompass both definitions, particularly when distinguishing “physiognomic” classifications from “floristic” ones. The basic unit of many physiognomic classifications is the formation, a "community type defined by dominance of a given growth form in the uppermost stratum of the community, or by a combination of dominant growth forms" (Whittaker 1962). Source. less