Note the small flower heads and serrate margins of the upper leaves. Part of an auricle is seen on the edge of the lowest leaf. Note the distinctive shape of the unopened flower heads.
An annual with a short taproot, prickly sow thistle is an erect plant with stout stems to one meter in height. The herbage is usually smooth. The lower leaves are pinnatifid to serrate, 6-30 cm long and 1-15 cm wide with petioles . Prominent auricles or lobes are found on the lower leaves, these with well rounded margins. On the stems, the leaves become reduced in size, and become less divided. The stem leaves are oblanceolate in shape and have rounded, clasping bases. The margins of all the leaves are spiny toothed (much more pointy than the leaf margins of Sonchus oleraceous.
The inflorescence is a corymb, with several small flower heads. The flower heads are 1.5-2.5 cm wide, with yellow rays. The glandular involucre ranges from 9-14 mm long.
Prickly sow thistle is found in disturbed pastures, fields, and roadsides.
A native of Europe, prickly sow thistle is found over much of North America.
In the Columbia River Gorge, it may be found from about Crown Point in the west to about Hood River, OR in the east between the elevations of 100'-900'.