One of the photos from Gifu, Japan shows a nameplate, presumably from some public garden somewhere, which claims that R. pomifera is a hybrid of R. glauca and R. rugosa. Someone in Japan seems quite convinced, but I can't seem to find any other mention of this. How likely is it? Shouldn't such a cross be sterile?
Since r. pomifera/villosa is shown on HMF using European illustrations from the 1500s and 1600s, I'd be interested to know how an east Asian rugosa (first introduced in Europe in the 1790s,) managed to cross with (European) rosa glauca, when their native ranges are separated by thousands of miles. Crossing would presumably have had to occur when the roses had overlapping ranges, but I know of no reason to think that they ever overlapped. Absent compelling DNA evidence, I'm very skeptical.
