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. Mel Tyree (ZJNU) for useful discussions about pneumatic experiments, 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.