2.1 Population sampling
We collected a total of 210 individuals from 43 populations of P. villosa in the field throughout its natural range in China (Table S1 & (Figure S1) and randomly sampled five to ten individuals from each population. We sampled individuals 20 m apart to avoid sampling a single clone more than once. In the field, we immediately put the fresh leaves into sealed bags filled with silica gel and then stored them in the laboratory in a -20℃ freezer until processing. We deposited one voucher specimen representing each population in the Herbarium of Qinghai-Tibet Plateau Museum of Biology (QTPMB), Northwest Institute of Plateau Biology, Chinese Academy of Sciences, China.