Acknowledgements
We thank Dr. H. Jochen Schenk (California State University, Fullerton) and Lucian Kaack (Ulm University) for valuable comments on an early version of this paper, Dr. Melvin Tyree (Zhejiang Normal University) for useful discussions about pneumatic experiments, two anonymous reviewers for helpful suggestions, and various colleagues from the botanical garden of Ulm University for assistance with sampling. XG, KC, and SJ acknowledge financial support by the German Research Foundation (DFG, project Nr. 410768178). SAMM acknowledges the Humboldt Foundation for a postdoctoral fellowship at Ulm University. The authors declare that there is no conflict of interest.