Prickly Lettuce

A tall plant (2 to 6 feet) with a loose, branching cluster of yellow flower heads. Flower heads small (ź inch wide) and composed only of ray flowers (usually 6 to 12). Leaves, which vary from 2 to 12 inches long, are alternate and generally lobed with prickly margins and an arrow-shaped base that clasps the stem. The lower mid-rib with rigid bristles. Leaves and stem ooze a milky liquid when injured.

Photographed at Ottawa - early August