perennial sow thistle

Perennial sow thistle, also called field sow thistle, is a very common exotic weed. It is native to Europe and Asia. It was introduced and naturalized into North America. It is now common across the northern half of the United States and it also occurs in the southwest. It is mostly absent from the southeast and south-central regions. It is very common in Minnesota. It is found in urban areas, on stream banks and roadsides, and in disturbed areas.

Perennial sow thistle is a tall plant with showy yellow flowers. Stems and leaves exude a milky sap when broken or torn. Lower leaves are deeply divided into more or less triangular lobes. Upper leaves are often shallowly lobed or unlobed. The leaf margins are toothed and prickly. The inflorescence is an array of up to 20 flower heads. Flower heads are yellow and large, up to 1¾″ in diameter when fully open.

Vegetatively, perennial sow thistle looks much like Canada lettuce, but that plant has much smaller, less showy flowers. Other sow thistles also have smaller flowers.

There are two subspecies of perennial sow thistle. Both are present in Minnesota. Sonchus arvensis ssp. arvensis is very common, S. a. ssp. arvensis is uncommon.

Sources

2, 3, 4, 5, 7, 22, 24, 28, 29, 30.

Plant

Flower

Leaves

Location: Woodbury, Minnesota