XVI International Botanical Congess

Phylogenetic studies using nuclear ribosomal SSU and ITS show that the Ectocarpales, Chordariales, Dictyosiphonales and Scytosiphonales (Ectocarpales s.l.) Form a distinct clade in the Phaeophyceae. Parsimony analyses of chloroplast-encoded rbcL and RUBISCO spacer sequences representing 42 genera, 36 of which belong to the Ecto-carpales s.l., verify the close relationship among these four orders. Substantial intermingling was observed between members of the Ectocarpales, Chordariales and Dictyosiphonales, whereas both Scytosiphonales and Ectocarpus-Kuckuckia form highly supported monophyletic clades. In conclusion, thallus and life history characters do not correlate with phylogeny in the way predicted by classification, whereas specialized chloroplast-pyrenoid constellations seem to circumscribe phylogenetic units.