I was visiting a friends rose garden tonight & he has a large bush of R. rugosa rubra in one area. He has started several new bushes off this mother plant by taking root cuttings. A couple of the new bushes are identical to the mother plant in all ways except they are producing flowers that are semi-doubles (12 -15 petal) were as the mother plant is very definitely a single. I could see no evidence of another rugosa near or mixed in the mother plant or the root transplants. Does R. rugosa rubra sometimes throw flowers with higher petal count?