Evidence from Hepatics on the History of the British Flora

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Abstract
The result of glaciation has been variously believed to have been complete extinction of the British flora and extensive survival in certain localities. Interpretation of distr. data for bryophytes is made more difficult by the poverty of field data and taxonomic confusion in some groups. The distr. of British hepatics having a disjunct world distr. is given in detail. They fall into 6 groups, the Mediterranean Element, Disjunct-Temperate Element (temperate Asia, Europe and N. America), American Element (W. Europe and N. America), Boreal-Tropical Element (scattered stations in n. temperate regions and tropics) Macaronesian-Tropical Element (western Europe, Azores, Madeira and Canary Islands and commonly some part of the tropics), and Other Disjunct Spp. In the British Isles the Mediterranean Element is centered on the south of England. The remaining elements have a markedly w. distr. By consideration of common spp. it is shown that bias due to unequal collecting is unlikely to be important except in the consideration of distr. within Ireland. The distr. of the western spp. is shown to accord well with areas having high values of Amann''s index of hygrothermy. Examples are given of non-British spp. of hepatics and of British spp. of other groups of plants having similar world distr. patterns. The distr. data are discussed in relation to the known climatic changes since the Glacial period. It is concluded that they can all be explained in terms of post-Glacial climatic change without invoking in situ survival.