1. Department of General Botany; Faculty of Biology; University Duisburg-Essen; Universitätsstr. 5 Essen D-45141 Germany
2. Department of Limnology of Stratified Lakes; Leibniz-Institute of Freshwater Ecology and Inland Fisheries; Alte Fischerhütte 2 Stechlin-Neuglobsow D-16775 Germany
3. SOA Key Laboratory for Polar Science; Polar Research Institute of China; Jin Qiao Road Shanghai 200136 China
4. Botanic Garden and Botanical Museum Berlin-Dahlem; Freie Universität Berlin; Königin-Luise-Str. 6-8 Berlin 14195 Germany
5. Grüner Weg; Niederzier D-52382 Germany
6. Department of Botany; Faculty of Science; University of South Bohemia; Ceske Budejovice 37005 Czech Republic