1. Department of Biology, University of Florida, P.O. Box 118525, Gainesville, FL 32611, USA
2. Co-first authors
3. Herbarium, UA Museum and Deparment of Biology & Wildlife, University of Alaska Fairbanks, 907 Yukon Dr., Fairbanks, AK 99775, USA
4. Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK; British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
5. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
6. Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269, USA
7. Department of Natural History, NTNU University Museum, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
8. Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, The Netherlands
9. Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
10. Département de Biologie, Université Laval, Québec, QC G1V 0A6, Canada; Smithsonian Tropical Research Institute, Ancon, 0843-03092 Panama, Republic of Panama