Storksbill (Erodium cicutarium)
These pretty little geranium flowers are astonishingly adaptable; they came from Europe, but have made themselves at home as far north as Greenland and as far south as Texas. In some places they are listed as a noxious wed. In the Pittsburgh area they are actually relatively rare, known only in Allegheny County and not yet found in any of the surrounding area. These were blooming in the middle of May near a railroad track in Bridgeville.
Gray describes the genus and the species:
ERÒDIUM L’Hér. STORKSBILL. The 5 shorter stamens sterile or wanting. Styles in fruit twisting spirally, bearded inside. Otherwise as Geranium. (Name from erodios, a heron.)
E. cicutàrium (L.) L’Hér. Annual, hairy; stems low, spreading; stipules acute; leaves pinnate, the leaflets sessile, 1-2-pinnatifid; sepals bristle-tipped; filaments not toothed. — About cities, not rare. (Adv. from Eu.)