Annuals or biennials, 15-450+ cm; taprooted. Stems usually 1, usually erect, branched distally or throughout, glabrous or hairy (sometimes hispid to setose). Leaves basal and cauline or mostly cauline (at flowering); sessile or petiolate; blades orbiculate, ovate, oblong, or lanceolate to oblanceolate, linear, or filiform, margins entire or denticulate to pinnately lobed (faces glabrous or hairy, often ± setose). Heads borne singly or in corymbiform to paniculiform arrays. Peduncles not inflated distally, sometimes bracteate. Calyculi of 3-10+, deltate to lanceolate bractlets in 2-3 series (sometimes intergrading with phyllaries). Involucres campanulate to cylindric, 2-5[-8+] mm diam. Phyllaries 5-13+ in ± 2 series (erect or reflexed in fruit), lanceolate to linear, usually subequal to equal, margins sometimes scarious, apices obtuse to acute. Receptacles flat to convex, pitted, glabrous, epaleate. Florets 6-50+; corollas yellow, bluish, or whitish. Cypselae reddish brown, tan, whitish, or purplish to blackish, bodies compressed to flattened, elliptic to oblong, beaks stout (0.1-1 mm, gradually or weakly set off from bodies) or filiform (2-6 mm, sharply set off from bodies), ribs 1-9 on each face, faces often transversely rugulose, usually glabrous; pappi persistent (borne on discs at tips of cypselae or beaks), obscurely double (spp. 1-2), each a minute, erose corona 0.05-0.2 mm subtending 40-80+, white or fuscous, ± equal, barbellate to barbellulate bristles in 1-2 series, or simple (spp. 3-10) of 80-120+, white, ± equal, barbellulate to nearly smooth bristles in 2-3+ series. x = 9. The common head and leaf lettuces of home gardens and commerce are derived from Lactuca sativa.