Plants 50-200 cm (short to long-rhizomatous, sometime colonial). Stems 1-10(-20), ascending to erect, striate, glabrous or sparsely hairy. Cauline leaves: mid and distal crowded, blades broadly to narrowly elliptic, (35-)60-110(-150) × (5-) 13-25(-35) mm, ± reduced distally, not stiff, bases attenuate, margins entire, involute, finely ciliate, apices acuminate, faces glabrous or sparsely hairy, especially along veins abaxially, or densely hairy. Heads (3-)20-100(-300+). Peduncles 1-10 mm, moderately to densely canescent; bracts linear-lanceolate to elliptic. Involucres 3-5 mm. Phyllaries in 3-4 series, triangular-lanceolate, midveins not swollen, apices finely subulate, strigose. Rays (2-)5-10(-16); laminae (4-)7-10(-12.3) × (0.8-) 1.2-1.8(-2.7) mm. Disc florets (5-)11-26(-50); corollas 3.5-6 mm, lobes 2-3.2 mm, 60-75% of limb. Cypselae 1.4-3.2 mm, 4-6-ribbed, sparsely to densely strigose; pappi: outer 0.2-0.8 mm, inner 3.5-6.2 mm. 2n = 18.
Plants (4-)10-20 dm from well developed creeping rhizomes; stem usually glabrous or nearly so below the infl; lvs all cauline, entire, finely reticulate beneath with well developed primary lateral veins, mostly 4-16 cm נ7-35 mm, sessile or nearly so and tapering to both ends, mostly rather narrowly elliptic or lance-elliptic and 4-6 times as long as wide, seldom broader; heads ±numerous (30-300+) in a corymbiform, generally dense infl that tends to be flat-topped; invol 3-5 mm, glabrous or somewhat puberulent, its bracts well imbricate, greenish but scarcely herbaceous, relatively thin and slender, seldom any of them as much as 1 mm wide, acute or obtuse; fls 23-54 per head, the rays (6)7-14, white, 5-8 mm, the disk-fls 16-40, ochroleucous; achenes sparsely to evidently strigose or puberulent; pappus double, the inner of firm, rather sordid bristles, the larger ones ±clavellate-thickened toward the tip, the outer less than 1 mm; 2n=18. Moist, low places; Nf. to Minn., s. generally to Va., Ky., and Ill., and in the mts. to n. Ga. and ne. Ala. (Doellingeria u.) Low and few-headed plants toward the ne. end of the range, with the stem and lower lf-surfaces often puberulent, may be varietally separable from the widespread, normally robust and many-headed typical phase, which has the stem generally glabrous or subglabrous below the infl, the lvs glabrous beneath (and often glaucous) or merely puberulent along the midrib and main veins, rarely sparsely so over the surface.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.