Common name: Smirnow rhododendron
Rhododendron smirnowii is native to the Caucasus Mountains around the tree line, hence it is very hardy. For this reason it has been used to breed winter-hardy rhodos. Roy Forster used it to create the yellow-flowered R smirnowii x 'Lady Bess' (which we do not have in the Garden)
The frilly flowers are pink. It was first collected in 1885 and named after a man called Smirnov.
Flower photo El Grafo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Photo of R. 'Lady Bess' by Roy Forster, from the City of Vancouver Archive.