Annuals (perhaps persisting), 15-70(-100+) cm. Leaves on proximal 1/2-3/4+ of each stem; blades of undivided cauline leaves ± linear to filiform, margins entire or denticulate, midribs usually prickly-setose. Heads in race-miform to spiciform arrays. Involucres 6-9(-13+) mm. Phyl-laries usually erect in fruit. Florets 6-12(-20+); corollas yellow (sometimes abaxially bluish), usually deliquescent. Cypselae: bodies pale brown, ± flattened, elliptic to oblanceolate, 2.5-3.5 mm, beaks ± filiform, (2-)5-6 mm, faces 5-7-nerved; pappi white, 5-6 mm. 2n = 18. Flowering Aug-Oct. Disturbed sites; 10-1500 m; introduced; Ont., Que.; Ala., Ariz., Ark., Calif., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Mo., Nebr., Nev., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Oreg., Pa., S.C., Tenn., Tex., Va., Wash., W.Va., Wis.; Europe; introduced also in Mexico.
From Flora of Indiana (1940) by Charles C. Deam
Local but abundant where it is found. No doubt it has a wider distribution than our map indicates. It prefers a sandy soil and in such a habitat it is a common weed in ballast for miles along railroads. Found along railroads and roadsides and waste places and pastures.
FNA 2006, McDougall 1973
Duration: Annual Nativity: Non-Native Lifeform: Forb/Herb General: Herbaceous annuals to biennials, glabrous, to 70 cm tall, stems slender, leafy, usually several arising from a taproot, decumbent at the base, with milky sap. Leaves: Alternate, linear-lanceolate, to 5 cm long, pale green, attenuate at the tips, bases arrowhead-shaped and clasping at the base, margins entire or the lower ones toothed or few-lobed, the midribs usually prickly-setose. Flowers: Heads small, ligulate, ligules yellow but sometimes bluish below, involucres cylindrical, 12-15 mm high, phyllaries overlapping in 2 or more series, usually erect in fruit, the heads in groups of 8-10, borne in narrow, spike-like panicles with short, ascending branches. Fruits: Achenes light brown, to 3 mm long, strongly flattened, contracted into a beak 5-6 mm long with a disk at the apex. Pappus of copious, white, early deciduous capillary bristles, 5-6 mm long. Ecology: Found in disturbed areas from 0-5,000 ft (0-1524 m); flowering August. Distribution: Somewhat widespread, from Ontario and Quebec south to Georgia and Alabama, west to Texas, Arizona, and California, extending north to Washington. Notes: Good identifiers for this species are the spinulose, oblong to elliptic leaves and the panicles with open, spreading branches. Introduced. Ethnobotany: Unknown Etymology: Lactuca is Latin for milky sap, while saligna means resembling the willow. Synonyms: None Editor: LCrumbacher 2011
Leafy-stemmed annual or biennial, the stem glabrous, 3-10 dm, more slender than in no. 7 [Lactuca serriola L.]; lvs conspicuously sagittate, linear and entire or with scattered, narrow, sometimes slightly toothed lobes, 6-15 cm, the rachis (or the lf, when entire) 3-8 mm wide, glabrous or with a few prickles on the midrib beneath and sometimes minutely stellate marginally; heads numerous in a long infl; fls 8-16, light yellow, drying blue; invol 12-18 mm in fr; achenes as in no. 7 [Lactuca serriola L.], but avg slightly smaller and narrower, merely scabrous distally, the beak commonly twice as long as the body; 2n=18. A weed in waste places; native of Europe, now found here and there in our range. Aug., Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.