Acknowledgements We thank Professor David Inouye who assisted in manuscript preparation. We also thank Sheng-Jun Huang, Li-Hui Zhang, and Er-Na Xun for their assistance in the field. This work was supported by grants from the National Natural Science Foundation of China to Yan-Wen Zhang (31170354) and to Ji-Min Zhao (31170384).
The occurrence of nectarlessness flowers in nectar-producing plants is a common and stable phenomenon in many species, but their occurrence is still not well understood. The aim of this study is to examine a question ...