Perennial Sowthistle (field milk-thistle) Asteraceae (=Compositae), the aster family
BACKGROUND: Perennial sowthistle is native to western Asia and Europe. It spreads both by seed and creeping roots, and it grows under a many conditions. Plants produce from root buds as deep as 2 feet, often resulting in large, dense colonies.
DESCRIPTION: Perennial sowthistle has crowded, spatula-shaped to deeply lobed, dandelion-like leaves up to 10 inches long near the base of the plant. Stem leaves are much reduced, usually unlobed, and scarce; all leaves are prickly toothed along the margins. Stems are hollow, sparsely branched, and up to 6 feet tall. Both leaves and stems exude a milky latex when broken. Yellow, dandelion-like flower heads are 2 inches wide and bloom from June until frost. The flower heads and their stems bear 
coarse, spreading, gland-tipped hairs. Seeds are reddish brown, 1/8 inch long, flattened, ribbed, and tipped with white plumes. The plant has extensive horizontal roots.
DISTRIBUTION: Perennial sowthistle is present in the northern U.S., and in California, Texas, Missouri, and North Carolina.
CONTROL: No biological control agents are available, but herbicides are.
© 1999 University of Idaho: Text and photographs for these pages from Idaho’s Noxious Weeds, by Robert H. Callihan and Timothy W. Miller (revised by Don W. Morishita and Larry W. Lass).
Please contact: Ag Publishing, University of Idaho, Moscow, Idaho 83844-2240; (208) 882-7982; [email protected]; or visit the UI Extension/CALS Publications and Multimedia Catalog website at www.cals.uidaho.edu/edComm/catalog.asp, for more information about this or other publications.
