1. Slovak Academy of Sciences; Institute of Botany; Dúbravská cesta 14, Bratislava 845 23 Slovakia
2. Université Joseph Fourier; Laboratoire d'Ecologie Alpine; UMR UJF-CNRS 5553, P. O. Box 53, Grenoble Cedex 9 38041 France
3. University of Fribourg; Unit of Ecology and Evolution, Department of Biologie; 1700 Fribourg Switzerland