1. Center for Climatic Research, University of Wisconsin, 1225 W. Dayton St., Madison, Wisconsin 53706 USA
2. Limnological Research Center, University of Minnesota, Minneapolis, Minnesota 55455 USA
3. Biology Department, Luther College, Decorah, Iowa 52101 USA
4. Department of Botany, University of Wisconsin, 430 Lincoln Drive, Madison, Wisconsin 53706 USA
5. Bureau of Natural Heritage Conservation, Wisconsin Department of Natural Resources, 101 South Webster Street, Madison, Wisconsin 53707 USA