1. UA Museum of the North Herbarium, Department of Biology and Wildlife, and Institute of Arctic Biology, University of Alaska Fairbanks, 907 Yukon Drive, Fairbanks, Alaska 99775‐6590 USA;
2. School of Life Sciences, Box 874501, Arizona State University, Tempe, Arizona 85287‐4501 USA;
3. Department of Botany, MRC‐166, Smithsonian Institution, P.O. Box 37012, Washington, D.C. 20013‐7012 USA;
4. Laboratory of Systematic and Evolutionary Botany & Herbarium, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China