A REVIEW OF THE GENUS NEMACYSTUS (SPERMATOCHNACEAE, CHORDARIALES, PHAEOPHYCEAE), INCLUDING PHYLOGENETIC AND BIOGEOGRAPHICAL HYPOTHESES

Phylogenetic relationships among the species of Nemacystus were inferr ed from morphological characters examined in herbarium specimens. Nema cystus is a very homogeneous genus. Species differ from each other in subtle morphological aspects of the dimensions and shape of assimilato ry filaments, plurilocular sporangia, colour, ramification, and genera l habit. Nemacystus erythraeus var. indicus is described as a new vari ety and Nemacystus flexuosus var. giraudii is proposed as a new combin ation for Mediterranean Nemacystus. A key to identify taxa of Nemacyst us is provided. A comparison of genealogy and biogeographical distribu tion reveals two groups of species, one with a north-westerly and the other with a south-eastern geographical occurrence. This probably refl ects a strong historical imprint of the Tethys Sea and negates a suppo sed monophyly of the Atlantic taxa.