A karyological study was made of the genus Scirpus L., section Schoenoplectus Benth. et Hook., in the Netherlands. It was found that the species S. lacustris L., S. tabernaemontani Gmel. and S. triqueter L. all have the same chromosome number of n = 21. S. americanus Pers. proved to have a different number (n = 39).