sow thistle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various plants of the genus Sonchus of the composite family, native to Eurasia and Africa but widespread as weeds, having prickly leaves, milky sap, and yellow flower heads.

from The Century Dictionary.

• noun A plant of the genus Sonchus, primarily S. oleraceus, a weed of waste places, probably native in Europe and central Asia, but now diffused nearly all over the world.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of the thistles in one of the genera Cicerbita and Sonchus.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of several Old World coarse prickly-leaved shrubs and subshrubs having milky juice and yellow flowers; widely naturalized; often noxious weeds in cultivated soil