CORN COCKLE, Agrostemma githago L. 1, plant in flower; 2, seed pod enclosed by the ribbed calyx; 3, seed. Winter annual, reproducing by seed. Taprooted, shallow. Stems rough, hairy, erect, 2 to 3 feet (60 to 90 cm) tall, swollen at joints, branching slightly. Leaves opposite and joined at base, slender, hairy. Flowers large, purple, with narrow, green sepals longer than colored petals. Seed pod holding several seeds, enclosed in a 10-ribbed urnlike calyx. Seeds black, about 1/8 inch (3 mm) in diameter, triangular, covered with rows of sharp tubercles. Seeds poisonous and therefore highly objectionable in grain used for milling or feed. Found especially on cultivated land and in association with fall-sown grain crops.