Could somebody identify this plant? They are commonly sold in wild flower nurseries in Korea. I heard that they are imported from Japan, but I am not sure if they are native to Japan.
Is it possible to get a more detailed photograph of the flowers, perhaps when the sun isn't so bright and overexposing the whites?
Yes, that should be more than detailed enough to identify it to family or genus, but I'm afraid I don't know what it is. I've checked my initial guesses against some books and came up short.
The flower structure makes me think of something in the subfamily Asclepiadoideae (former family Asclepiaceae) - compare e.g. the flowers of Asclepias or Hoya. The leaves are very different to those two genera though.
Could it possibly be in Rhamnaceae? Except for the petal-like structure surrounding the pistil the flowers resemble Ceanothus.