Rhododendron arboreum subsp. zeylanicum (Booth) Tagg, Species of Rhododendron 16 1930 (syn: Rhododendron zeylanicum Booth);
Sri Lanka as per CoL;

Rhododendron arboreum subsp. zeylanicum from UCBG-GS28082021-1: 3 images.

Rhododendron arboreum subsp. zeylanicum (Booth) Tagg
Syn: R. zeylanicum Booth
Locally known as Maha Rath Mala, the tree is endemic to highlands of Sri Lanka. It is official Flower of Central Province. Details can be found here:

Photographed from University of California Botanical Garden, 22-4-2019.





References: Catalogue of Life  POWO  The Plant List Ver.1.1  IPNI  GBIF (High resolution specimens) Wikimedia Commons   rhododendron  treesandshrubsonline