Perennials, 30-200+ cm (rhizomatous, stoloniferous, or with basal offshoots). Stems erect to ascending, branched distally (ribbed), glabrous. Leaves basal (withering by flowering) and cauline; alternate; sessile (sometimes decurrent); blades 1-nerved, linear, subulate to lanceolate or oblanceolate (bases attenuate, cauline sometimes decurrent), margins entire to serrulate (teeth callous-tipped), (apices acute to acuminate) faces glabrous. Heads radiate , (10-100+) in leafy, corymbiform or paniculiform arrays. ( Peduncles bracteate or ebracteate, bracts leaflike or scalelike .) Involucres hemispheric, (2-5 ×) 3-14 mm. Phyllaries 30-55 in 3-6 series, 1-nerved (midribs thickened, resinous; flat), linear to oblanceolate or spatulate, unequal to subequal, margins ± membranaceous, faces glabrous. Receptacles conic to hemispheric, obscurely pitted, epaleate. Ray florets 20-60, pistillate, fertile; corollas white to lilac (laminae linear to elliptic). Disc florets 50-400+, bisexual, fertile; corollas yellow, tubes shorter than funnelform throats, lobes 5, erect, triangular; style-branch appendages deltate. Cypselae dimorphic (brownish); ray ± triquetrous, margins arrowly winged, ribs 2 abaxial, 1 adaxial; disc obovoid to cuneate or obcordiform, laterally compressed, margins winged or not, resin ducts present, faces often puberulent; pappi persistent, usually of 2-3 sclerified awns plus (0-)7-12 shorter bristles or scales in 1 series. x = 9.
Heads radiate, the rays white to pink or blue, pistillate; invol bracts subequal to strongly imbricate, scarious-margined, with green or greenish midrib or tip; receptacle hemispheric or conic, naked; disk-fls yellow, fertile; style-branches flattened, with short, lanceolate, externally hairy appendage; achenes obovate, strongly flattened, ±wing- margined; pappus of several minute bristles and 2(4) longer awns, these commonly reduced or wanting in the ray-achenes, sometimes also in the disk; glabrous, often stoloniferous, short- lived perennials with relatively narrow, chiefly entire lvs and several to very many small to middle-sized hemispheric heads. 5, U.S.A.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.