THE GEOGRAPHICAL RELATIONSHIPS OF BRITISH AND IRISH VASCULAR PLANTS

Classifications of British and Irish vascular plants into floristic el ements are reviewed. Only H.C. Watson and J.R. Matthews have attempted to devise a more or less comprehensive classification, based on the B ritish range of the species (Watson) or the European distribution (Mat thews). A new classification of 1481 native species is presented, base d on their range in the Northern Hemisphere. Species are classified by their occurrence in one or more major biomes (Arctic, Boreal, Tempera te, Southern) and their longitudinal distribution (Oceanic, Suboceanic , European, Eurosiberian, Eurasian, Circumpolar). The distribution of species in the Aoristic elements is illustrated by coincidence maps fo r the British Isles and Europe. The British and Irish flora is dominat ed by Boreo-temperate, Temperate and Southern-temperate species, with the Temperate species being the most numerous. Species with continenta l distributions (i.e. species which are rarer than expected in western Europe) are listed; most of these are in the Boreo-temperate and Temp erate elements. The floristic elements are discussed in relation to th e life-form spectra, habitat preferences and altitudinal limits of the component species, and analysed in terms of Ellenberg indicator Value s for temperature and continentality. The new classification is compar ed with that of Matthews. An additional 48 species which are endemic t o the British Isles are listed. The scope for extending this method of classification to other organisms and for adapting it for use outside the British Isles is discussed. (C) 1997 The Linnean Society of Londo n.