The importance of closely related taxa for the delimitation of phytosociological units

Abstract

Phytosociological importance of closely related taxa has already been stressed by numerous authors. Difficulties in using closely related taxa as characteristics of a given plant association are mainly due to our insufficient knowledge of their biosystematics; the real status of many proposed units (e.g. microspecies, subspecies, variety, forma) is often not precised and it is often even not known whether the diagnostic characters are hereditary or merely represent some modifications. Furthermore, the ecological differentiation may show regional or local differences. Thorough experimental studies in many critical plant groups are required. The behaviour of closely related taxa under different ecological conditions is shown in Fig. 2. Various trends are exemplified by several groups of species: Molinia coerulea, Centaurea Jacea, Cardamine pratensis, Scobiosa columbaria, also some Alpine vicariants on siliceous and calcareous soils. Closely related taxa used in the phytosociology will not show any new criteria for delimitation of vegetation units, but often increase the number of characteristic components. Accordingly, actual limits of a given unit become better documented and more ecological information will be gathered.