ECOLOGICAL AND HISTORICAL FACTORS IN THE DISTRIBUTIONS OF THE BRITISH HELIANTHEMUM SPECIES.

The article focuses on the ecological and historical factors in the distributions of the British Helianthemum species. Among the specie of these plants is the Helianthemum chamaecistus which is widely distributed in short dry chalk and limestone grasslands in Wales and England. It is dominated by Festuca ovina, Seslerina caerulea, and Zerna erecta, and appears in substrata in dry Agrostis tenuis-Festuca ovina grasslands in Scotland. On the other hand, H. apenninum is confined to open xeric grasslands on slopes that faces south on Carboniferous and Devonian limestones in Southwest England.