Perennials, 40-250 cm, colonial; long-rhizomatous. Stems 1, erect (straight, ± thin, 2-8 mm diam at base, ± ribbed, red above each node), glabrous or glabrate (very sparsely hispidulous) proximally to ± hispidulous distally. Leaves (crowded, light green, shiny) firm, margins crenulate-serrate or entire, revolute, apices acute to acuminate, mucronate, abaxial faces glabrous or midveins sometimes with hairs apically, adaxial glabrous; basal withering by flowering, subpetiolate (petioles dilated, winged, sheathing), blades spatulate to oblanceolate, 30-100+ × 3-20+ mm, bases attenuate to cuneate, margins remotely crenate-serrate to subentire, apices acute to rounded; proximal cauline withering by flowering, sessile or subpetiolate (petioles widely winged, clasping), blades oblanceolate, 50-150 × 20-30 mm, greatly reduced distally, bases auriculate, clasping, apices acute to acuminate; distal sessile, blades lanceolate to lance-elliptic to oblanceolate, 40-70 × 10-25 mm, little reduced distally, bases auriculate, clasping, margins entire, apices acute to acuminate. Heads in densely paniculiform arrays, branches ascending, densely leafy (branch leaves often overtopping heads). Peduncles 0.2-3+ cm, glabrous or pilose in lines, bracts 4-6, lanceolate-linear, often subtending heads. Involucres campanulate, 6-12 mm. Phyllaries in 4-5(-6) series, linear-lanceolate to linear, slightly unequal, bases indurate ¹ / 5 - ¹ / 2 , margins not scarious (outer) to narrowly scarious, erose, hyaline, sparsely ciliolate, green zones linear-lanceolate, outer sometimes ± foliaceous, apices acute to acuminate or long-acuminate to caudate, faces glabrous. Ray florets 20-40; corollas usually blue to pale lavender, sometimes white, laminae 9-18 × 1.0-1.2 mm. Disc florets 30-50; corollas yellow or cream becoming pink or purple, (4.5-)5-6.4 mm, tubes shorter than funnelform throats, lobes triangular to lanceolate, 0.6-0.9 mm. Cypselae purple or brown, obovoid, oblong or oblanceolate, ± falcate, ± compressed, 1.5-3 mm, 3-4-nerved, faces glabrous or sparsely strigillose; pappi white, 5.2-8 mm. 2n = 16. Flowering Aug-Oct. Open, wet soils, spreading into mesic mineral soils, fens, marshes, wet roadsides; 100-400 m; Alta., Man., Ont., Sask.; Ga., Iowa, Mich., Minn., Mo., Nebr. The range of this little known species is badly defined because some specimens attributed to it are in fact white-rayed, glabrate forms of Symphyotrichum puniceum. More work is needed to verify the status of this species.