I was growing this plant in Hamilton Square Garden but never posted a photo as I wasn't completely sure of the ID. It's what came to mind when I saw your plant based on the leaves. I had never noticed the buds shape on my plant but now that I look closer I see the wings. Plains Sundrops (Oenothera serrulata subsp. serrulata) Just a guess on my part but Tofi is correct on the Genus though it is now Oenothera according to COL.
