Appendix 1: Possible future additions to list above
"Hydrangea caucana Engl., H. durifolia Briq. and H. schlimii Briq. have not been collected recently and are known with certainty from nine herbarium specimens, the type collection and a putative additional herbarium specimen, or the type collection only, respectively. The three of them are endemic to Colombia, where we have not yet been able to collect Hydrangeas due to collection permit and export regulations."
Source: Samain, Marie-Stéphanie et al. (2021). On Hydrangea peruviana, an endangered species from Ecuador, and Hydrangea oerstedii, very common in Costa Rica and Panama, and seven threatened Central and South American Hydrangeas, which have been confounded with these. PhytoKeys 171: 91-153. doi: 10.3897/phytokeys.171.56351