5 petal perennial blooms in late May early June in zone 5.
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In US? "Zones" outside US/Canada have little use. Could you tell us about the size and may add photo of the plant (with leaves). 10 stamens, I would say Geranium. – Giacomo Catenazzi Jun 7 '19 at 9:11
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Do you have any picture that shows the leaves? Plants are actually easier to identify by leaf than by a single flower. You need to give a detail description of the plant, if you do not have a better picture. Without it my best guess would be some kind of perennial geranium. Not the large red flowered annual, which is not actually a geranium. A true geranium. But, that is just a shot in the dark. That is why I did not include under answer – GardenGems Nov 4 '19 at 6:37
It is Malva sylvestris. Wikipedia: