SPANISHNEEDLES, Bidens bipinnata
L. 1, lower portion of plant; 2, upper portion of stem and
flower heads; 3, mature flower; 4, seed. Annual, taprooted
with numerous side branches. Stems erect, smooth, branching in upper
portions. Leaves with petioles, divided several times into fine
segments; borne opposite at nodes of both stems and branches. Flower
heads found singly at the ends of long, slender, nearly leafless
branches, pale yellow ray flowers surrounding yellow disk flowers. Seeds
about 1/2 inch (1.3 cm) long, narrow, sharp-pointed, brown to black, bearing
3 to 4 stiff spines covered with short, down-pointed bristles. Found
in waste places and grain stubble fields.