POWO:
Pileostegia viburnoides Hook.f. & Thomson is a synonym of Hydrangea viburnoides (Hook.f. & Thomson) Y.De Smet & Granados
https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:792369-1

De Smet, Y., Granados Mendoza, C., Wanke, S., Goetghebeur, P., & Samain, M. S. (2015). Molecular phylogenetics and new (infra) generic classification to alleviate polyphyly in tribe Hydrangeeae (Cornales: Hydrangeaceae). Taxon, 64(4), 741-753.
https://onlinelibrary.wiley.com/doi/pdf/10.12705/644.6