Rhododendron schlippenbachii Maxim., Bull. Acad. Imp. Sci. Saint-Petersbourg 15: 226 1871. (syn: Azalea schlippenbachii (Maxim.) Kuntze; Rhododendron schlippenbachii f. albiflorum Y.N.Lee);
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S. Russian Far East to N. China and Japan: Inner Mongolia, Japan, Korea, Manchuria, Primorye as per POWO;
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Rhododendron schlippenbachii Maxim.: 4 very high res. images.
Habit : Cultivated
https://www.flickr.com/search/?user_id=11713966%40N02&sort=date-taken-desc&text=Rhododendron%20schlippenbachii&view_all=1one
I was also sceptical about the ID but the label says so !
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References:
POWO Catalogue of Life The Plant List Ver.1.1 Tropicos IPNI Flora of China Wikipedia Flickr
https://plants.ces.ncsu.edu/plants/rhododendron-schlippenbachii/
https://landscapeplants.oregonstate.edu/plants/rhododendron-schlippenbachii
https://www.finegardening.com/plant/royal-azalea-rho%C2%ADdodendron-schlippenbachii