1. Department of Ecology and Natural Resource Management; Norwegian University of Life Sciences; PO Box 5003 NO-1432 Ås Norway
2. Section for Genetics and Evolutionary Biology; Department of Biosciences; University of Oslo; PO Box 1066 Blindern NO-0316 Oslo Norway
3. Norwegian Forest and Landscape Institute; Fanaflaten 4 NO-5244 Fana Norway
4. Department of Botany; Natural History Museum; University of Oslo; PO Box 1172 Blindern NO-0318 Oslo Norway