1. Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701 USA
2. Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331 USA
3. Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada
4. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK