Snow-on-the-Mountain (Euphorbia marginata)
A native of the Midwest, but so often cultivated in the East that it has become an established weed, especially in old city lots and along railroad tracks. This colony grew along a residential street in Beechview. It makes an attractive cut flower, but the stems have a milky sap that may be irritating to the skin.
From Gray’s Manual of Botany: E. marginata Pursh. (SNOW-ON-THE-MOUNTAIN.) Stem stout, 3-9 dm. high, erect, hairy; leaves sessile, ovate or oblong, acute; umbel with three dichotomous rays; glands of the involucre with broad white appendages. Minn, to Mo., Col., Tex., and S. C.; spreading eastw. to O., and frequently escaping from flower-gardens.