Annual, biennials, or perennials, 10-80 cm. Stem bases soft to hard, herbaceous, often hollow. Leaves: blades of mid cauline oblong, 3-20 × 2-6 cm, bases auriculate, auricles ovate to lanceolate or linear, ± straight, obtuse to acute, margins usually pinnately lobed, lobes ± rhombic to lanceolate (constricted at bases) or ± linear, terminals ± equaling laterals, entire or dentate. Peduncles usually setose- to stipitate-glandular, often tomentose as well, sometimes glabrous. Involucres 10-12+ mm. Phyllaries usually setose- to stipitate-glandular, sometimes tomentose as well. Corollas: ligules longer than tubes. Cypselae reddish brown, oblanceoloid, 2.5-3.5 mm, ribs 1-3 on each face, faces transversely rugulose or tuberculate across and between ribs; pappi 5-8 mm. 2n = 14.

Flowering Mar-Jun. Disturbed sites, often on ballast; 0-200 m; introduced; Calif.; s Europe, w Asia, n Africa.

Sonchus tenerrimus was known historically on ballast from Alabama, Pennsylvania (Philadelphia), New Jersey, New York, and, possibly, Quebec.