XVI International Botanical Congess

To date, morphological characters did not allow to infer a consistentphylogeny of the Phaeophyceae. Since the early nineteens, the recent use of molecular sequences allowed a better understanding of the evolution of this group: 1) a clade in which all representatives possess an exserted and pedunculated pyrenoid was pointed out, this led to redefine the Ectocarpales, 2) the polyphyly of the Laminariales was assessed, 3) the order Scytothamnales was created, 4) the order Fucales was re-defined including Notheia and Durvillaea. A first attempt to construct a comprehensive phylogeny has been based on combined partial LSU and SSU rDNA sequence data. It included one or more representatives (at least the type genus) of the currently accepted orders. The monophyly of most orders as well as the four results already cited above were confirmed. Also, the polyphyly of the Tilopteridales was revealed, and the monophyly of a Syringodermatales, Sphacelariales and Dictyotales assemblage was pointed out. However, the relationships between the other lineages appeared unresolved, suggesting a possible rapid radiation.