3. Sonchus oleraceus Linnaeus, Sp. Pl. 2: 794. 1753.
Common sow-thistle, laiteron
Annuals or biennials, 10–140(–200) cm. Stem bases soft to hard, herbaceous, often hollow. Leaves: blades of mid cauline spatulate or oblong to obovate or lanceolate, 6–35 × 1–15 cm, bases auriculate, auricles deltate to lanceolate, ± straight, acute, margins usually pinnately (often runcinately) lobed, lobes ± deltate to lanceolate, not constricted at bases, terminals usually larger than laterals, entire or dentate. Peduncles usually glabrous, sometimes stipi-tate-glandular. Involucres 9–13+ mm. Phyllaries usually glabrous, sometimes tomentose and/or stipitate-glandular. Corollas: ligules ± equaling tubes. Cypselae dark brown, mostly oblanceoloid, 2.5–3.5+ mm, ribs 2–4 on each face, faces transversely rugulose or tuberculate across and between ribs; pappi 5–8 mm. 2n = 32, 36.
Flowering (Apr–)Jul–Oct (year-round in south). Disturbed sites, gardens, roadsides, along streams; 0–2000 m; introduced; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kansas, Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Europe; introduced also in Mexico, West Indies, Bahamas, Central America, South America, Africa, Asia, Pacific Islands (New Zealand), Australia.