Rosa foliolosa is such a pretty species, I don't know why I haven't used it in breeding more than I have. I acquired this plant about 10 years ago when someone kindly sent me a few seeds collected from their plant. I don't know how mine measures up against other specimens but it is a very handsome plant and a beautiful flower. Mine is a very "rugosa rubra" hue of magenta and the flower is large: about 2.5 inches across. It starts to flower fairly late compared to the native R. nutkana and a bit after R. virginiana, and well after R. rugosa. Blooms have an excellent "wild rose" fragrance. R. foliolosa is listed as a diploid and so I am using it in breeding with that fact in mind.
If you read the descriptions of R. foliolosa, it is repeatedly stated that this is a low-growing, suckering shrub between 18" and perhaps as much as three feet. It is frequently referred to as thornless as well. Now, my specimen is a non-suckering shrub nearly 6 X 6 feet, with an average number of small, hooked thorns. The bloom color is generally listed as being white to pale/medium pink, where my plant has deep magenta blooms. I have a vague recollection that the person who gave me the seed stated that (for reasons I do not recall) they thought these seeds may be hybrids and not pure R. foliolosa. The fact that my plant deviates significantly from the average description makes me wonder if it isn't in fact a hybrid with something else, probably another species? Who knows. Since I know this is both seed and pollen fertile, the possibility of it being a hybrid makes it potentially even more valuable as a breeder.
One thing I can tell you is that years ago I made a cross of my R. foliolosa X 'Little Chief' and the three seedlings I saved all have some degree of remontancy. One of these three looks remarkably like 'Basye's Purple'! (more about that plant soon) And so, I think its high time I put this plant to work in my breeding.
Oh, one last thing: I have some seeds collected from this plant that are last year's crop. They are likely still fertile, and I am willing to distribute some of these with other hybridizers who are interested. Comment if you want to try germinating these.