WAN, XIA, CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization, Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, Chengdu, Sichuan 610041, China; College of Life Sciences, Sichuan University, Chengdu 610065, China; University of Chinese Academy of Sciences, Beijing 100049, China; Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, U.S.A., China