TAXONOMY OF PILAYELLA-LITTORALIS (L) KJELLM (PHAEOPHYTA, ECTOCARPALES) IN THE BRITISH-ISLES, A NUMERICAL APPROACH

The taxonomy of Pilayella littoralis (L.) Kjellm. is confused due to the extreme variability of the species. A numerical taxonomic study has been carried out using computer clustering techniques on 71 morphological and ecological characters with 163 plants from a wide range of habitats in Britain, and the status of the clusters formed scrutinized with reference to the original data. On this basis certain clusters were grouped together as seasonal variants of similar entities. Estuarine plants tend to have in common a number of characteristics which separate them from those collected in marine habitats, such as a much higher incidence of opposite branching and considerably finer filaments. A number of other environmental gradients other than salinity can be associated with these characteristics, for example substrate, exposure etc. The fact that seasonal morphological variation is also common, especially in marine populations, underlines the complexity of the relationship between environment and form in the species, and it is concluded that the establishment of a practicable natural classification of intraspecific variation in P. littoralis is impossible. © 1979 Taylor & Francis Group, LLC.