Marine Algae Have Their Taxonomic Challenges Too <B>Marine Algae Have Their Taxonomic Challenges Too</B><P> </B><EM><B></B></EM><B>W. F. Prud'homme van Reine</B><BR> Research Institute, Rijksherbarium/Hortus Botanicus, Leiden University, PO Box 9514, 2300 RA Leiden, The Netherlands<B></B><P> "Algae" is the name for a polyphyletic group of organisms, studied by phycologists. Some groups of these photosynthetic organisms are phylogenetically mutually less related to each other than sponges are to elephants. There is an excessive amount of very diverse higher taxa: divisions or phyla and many classes.<BR> Nobody knows how many algae exist. According to recent estimates the number of described species of eukaryotic algae is between 35,000 and 45,000, included in at least 9 phyla and 20 different classes. Estimates of the real number of existing species differ even more, between 150,000 and more than 10 million. Of these, especially the contribution of the diatoms is under discussion, where estimates differ between a minimum of 100,000 and a maximum of 10 million different expected extant species.<BR> Thus especially in the micro-algae many species occur or are at least expected to occur. There is also the genera with the largest numbers of described species are found. In the macro-algae, viz. the multicellular species of the classes Chlorophyceae, Ulvophyceae and Charophyceae (all are green algae), the Phaeophyceae (the browns), Xanthophycear (the yellow-green algae) and the division Rhodophyta (the reds), the large genera contain 380 or less species. Usually, all the largest genera contain 380 or less species. Usually, all macro-algae genera with more than 50 different species are considered to belong to species-rich grups. Of these, recent taxonomic research in marine groups will be discussed viz. in the red <I>Dasyacear</I>, the brown algal genus<I> Sphacelaria</I>, and the green algal genera <I>Cladophora</I> and <I>Caulerpa</I>.<P>