While a nice and very old European evergreen garden azalea, it seems unlikely that the deciduous azalea 'J.C. van Tol' is actually the pollen parent, based on the leaf morphology to be quite normal for an evergreen azalea. Also, the whiteness of the flower is not suspected giving the species nature of the seed parents. It seems more likely this is a hybrid between a white form of R.kaempferi and R.mucronatum. DNA research by Scariot et al 2007 seems to confirm the link to R.mucronatum.
