Lactuca serriola L.
Family: Asteraceae
compass-plant, prickly lettuce
Lactuca serriola image
Merel R. Black  
Etymology: Lactuca: name for "milk"
Plants: erect, annual/biennial, 1'-5' tall forb with milky juice; stems leafy, smooth except for prickles at the bottom
Leaves: varying from entire, toothed, to pinnately-divided with narrow to arrow-shaped base, spiny edges and midrib
Flowers: head 3/8" wide with 18-24 yellow rays, drying to a bluish-white; inflorescence with many heads in a long, conical, loosely-branched cluster; blooms July-Sept.
Fruits: dry seed with several obvious lines on both sides
Habitat: disturbed sites, fields
Hazardous: Careful, this plant is hazardous!
Conservation Status: Introduced - naturalized