Agrostemma githago  
Family: Caryophyllaceae
corn cockle
Agrostemma githago image
Dan Tenaglia  
Etymology: Agrostemma: from Latin for "field chaplet"
Plants: erect, annual, 2'-3' tall forb with thin hairs
Leaves: opposite, untoothed, without stipules, long and narrow
Flowers: pink to reddish, 5-parted, 1"-1 1/2" wide, sepals much longer than the petals and forming a 10-ribbed tube, petal tips with a small notch; solitary, terminal, stalked flowers; blooms July-Sept.
Fruits: capsule
Habitat: dry; disturbed sites
Hazardous: Careful, this plant is hazardous!
Conservation Status: Introduced - adventive
Agrostemma githago image
Emmet J. Judziewicz  
Agrostemma githago image
from USDA Plants website  
Agrostemma githago image
Botanical Illustration  
Agrostemma githago image
Kurt Stüber