Sonchus asper (Spiny Sowthistle) Family: Asteraceae (Sunflower)
     
The leaves of Sonchus asper have rounded basal lobes that clasp the stem. Leaf margins are spiny. Plants have a milky juice.

Compare to Sonchus arvensis, which has glandular hairs on the outside of the flower heads.
Compare to Sonchus oleraceus, which has broader, deeply lobed leaves with poorly developed or lacking spines.

Vegetation zone:  Plains, Foothills
Time of bloom:  July - October
Origin:  Introduced