S. arvensis: stems 2-3 feet high; leaves long, runcinately-pinnatifid or sinuate, the lobes lanceolate or triangular, bordered by small prickly teeth, the upper ones clasping the stem with short broad auricles; flower-heads large, bright yellow, in loose terminal panicles, the branches, peduncles, and involucres more or less hispid with brown or black glandular hairs. - A cornfield weed. Fl. August.
S. oleraceus: annual; stem thick, hollow, 1-4 feet high, glabrous; leaves thin, pinnatifid, with a broad, heart-shaped or triangular terminal lobe, bordered with irregular, pointed or prickly teeth, and a few smaller lobes or coarse teeth along the broad leafstalk, the upper leaves narrow and clasping the stem with short auricles; flower-heads rather small, pale yellow, in a short corymbose panicle, sometimes almost umbellate. - A weed of cultivation. Fl. June to August.
Var. aspera: leaves darker, less divided, but much more closely bordered with prickly teeth; clasping auricles broader, rounded, and more prickly toothed.