Sonchus asper (L.) Hill
Family: Asteraceae
prickly sow-thistle, spiny sow-thistle, spiny-leaf sow-thistle
Sonchus asper image
Paul Drobot  
Etymology: Sonchus: the Greek name for sowthistle
Plants: erect, annual, 4"-80" tall, mostly hairless forb with milky juice
Leaves: alternate, often not lobed, heart-shaped bases clasping and curving around the stem, toothed to pinnately-divided, edges quite prickly, upper leaves smaller and less divided
Flowers: head 1/2"-1" wide with pale yellow ray flowers; inflorescence of several heads in open, branched clusters; blooms July-Oct.
Fruits: dry, unwrinkled seed faintly 3-5 ribbed on each side
Habitat: disturbed sites