1. Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences , Guangzhou 510650 , China
2. Guangxi Institute of Botany, Guangxi Zhang Autonomous Region and the Chinese Academy of Sciences , 541006 Guilin , China
3. Department of Ecology and Evolutionary Biology, University of Arizona , 1041 E. Lowell St., Tucson, AZ 85721 , USA