ecology a plant community of some particular kind or grade —note 1. usage of the term varies greatly from one ecological school to another: (a) in most non-British schools, an association is the fundamental unit of plant ecology and is the equivalent of species in taxonomy, includes many local subassociations and facies (roughly equivalent to subspecies and varieties respectively in taxonomy), and defined mainly by floristic composition not by habitat, (b) in most of North America and Britain, the term follows Clements and refers to a major subdivision of formation restricted to (the presumed) climax communities —note 2. in both (a) and (b), an association may have several dominants, either mixed together or occurring in different places —see society This definition last updated 10/23/2008