A REDESCRIPTION OF LITHOPHYLLUM-ORBICULATUM (RHODOPHYTA, CORALLINALES) IN THE BRITISH-ISLES AND A REASSESSMENT OF GENERIC DELIMITATION IN THE LITHOPHYLLOIDEAE

A redescription is given of Lithophyllum orbiculatum (Foslie) Foslie and of its taxonomy, structure, conceptacle initiation and ecology in the British Isles. Due to a misidentification by Foslie, perpetuated by Rosenvinge, Suneson and Adey among others, this name has been erroneously applied to plants from the British Isles, Denmark, Iceland and North America that should be known as L. crouanii Foslie. The application of L. orbiculatum in France has, however, been consistent with the type. The origins of the nomenclatural and taxonomic confusion are documented and the relationships of L. orbiculatum to L. crouanii, and also to L. incrustans Philippi, with which it is often closely associated, are discussed. Generic delimitation within the Lithophylloideae is reconsidered in the light of recent publications; Titanoderma is retained as a separate genus. © 1991 British Phycological Society.