Perennials, 15-35(-45) cm, colonial or cespitose; rhizoma-tous. Stems 1-3+, ascending to erect (sometimes purple or purplish brown), glabrous or glabrate, sparsely hairy in leaf axils [villous to sericeous]. Leaves thin, apices callous-pointed, faces glabrous or glabrate; basal usually withering by flowering, long-petiolate, petioles sheathing, sparsely ciliate, blades lanceolate, 40-110 × (3-)5-7 mm, bases attenuate, margins entire to crenulate, rarely with 1-2 teeth, apices obtuse to rounded, callus-pointed; proximalmost cauline sometimes withering by flowering, winged-petiolate or sessile distally, blades lanceolate to linear-lanceolate, 50-120(-180) × 1-6 mm, bases attenuate, margins entire, sparsely ciliate, apices acute; distal sessile, blades subulate to lanceolate, 10-50 × 1-2 mm, bases clasping, apices acuminate. Heads (1-)3-20(-40), in paniculiform arrays, branches patent. Peduncles 1-4(-6) cm, ascending, glabrate, bracts 1-4(-5), subulate to lanceolate, foliaceous. Involucres cylindric to hemispheric, (4.5-)5-7.3 mm. Phyllaries in 2-3(-5) series, subulate to lanceolate, bases indurate, margins hyaline, entire to erose, often ciliate, green zones linear-lanceolate (outer) or rhombic (inner), apices acute, faces glabrous [sparsely villous]. Ray florets 14-27; corollas white, laminae (4.6-)5.6-7(-9.5)-10.3 × 1.3-2 mm. Disc florets 18-35(-42); corollas yellow, 3.5-5 mm, tubes shorter than funnelform throats (hairy), lobes± spreading, triangular, 0.5-0.7 mm. Cypselae light brown to gray, narrowly obovoid to fusiform, sometimes ± compressed, 2-3 mm, 5-nerved, faces glabrate to sparsely strigillose; pappi white to cream, 3.5-5.5 mm. 2n = 10.

Flowering (Jun-)Jul-Sep. Moist, muddy, sandy, or rocky soils along streams; of conservation concern; 1500-1900 m; Ariz.; Mexico.

Symphyotrichum potosinum is known from Cochise County, Arizona, south into Mexico to northern Oaxaca.