Studies in the genus Fucus L. II. Distribution and ecology of forms of Fucus distichus L. emend. Powell in Britain and Ireland

The distribution and ecology of subspp. anceps and edentatus of F. distichus L. emend. Powell (1957) in Britain and Ireland is described in detail, based on recent ecological surveys and critical examination of all past records. F. distichus anceps is a small form confined to certain very exposed coasts in the north and west of Scotland and Ireland, where it reaches the southern limit of its geographical range. This plant may be a relict form in Britain, existing now only under an extraordinarily narrow range of rigorous habitat conditions; it is not thought to be actively extending its range southwards at the present time. The ecology of subsp. anceps is considered principally in relation to that of other reduced fucoids found on exposed British shores, viz. F. spiralis f. nana and F. vesiculosus f. linearis ; all three forms are illustrated by photographs and means of distinguishing them are described. The lifespan of subsp. anceps is thought to be 2 to 3 years at some Irish sites, but may be longer at some of the Scottish sites.