Perennials, 7-39 cm, cespitose; slender, woody, short-rhizomatous (rhizomes of season shallow- or deep-seated, not producing ro­settes near parent stems). Stems 1, ascending to decumbent (slender, green to reddish brown), glabrate or sparsely short woolly-pilose in lines or zones, more densely so distally. Leaves (light green, abaxial sometimes becoming much darker) thin to firm, margins entire, scabrous, apices mucronulate, faces glabrous; basal persistent or withering by flowering, petiolate, blades oblanceolate to short-spatulate, 10-130 × 2-8 mm, bases cuneate to attenuate, margins rarely sparsely serrulate, apices obtuse, faces glabrous; proximal cauline persistent or withering by flowering, sessile, blades oblanceolate to linear lanceolate, 13-60 × 2-6 mm, bases ± clasping, apices acute; distal sessile, blades linear to linear-lanceolate, 10-36 × 1-4 mm, reduced distally, bases subauriculate, subclasping to ± clasping. Heads usually borne singly or in open, paniculiform arrays (sometimes terminating lateral branches arising from decumbent stems or from proximal stem branches), branches few. Peduncles 10-70 mm, sparsely to moderately short-strigose, bracts 0-10, lanceolate, often foliaceous, reduced distally. Involucres cylindro-campanulate, 4.7-7.4 mm. Phyllaries in 3-4 series, outer spatulate, inner lanceolate, ± unequal to subequal, bases indurate, margins reddish, papery, erose-ciliate, green zones lanceolate, apices acute, faces glabrous. Ray florets 15-41; corollas white to pale rose, often becoming rose-violet, laminae 5-13 × 0.7-1.8 mm. Disc florets 20-60; corollas yellow turning reddish with age, 3.7-6.6 mm, tubes shorter than funnelform throats, lobes erect to spreading, lanceolate, 0.4-0.8 mm. Cypselae tan (nerves stramineous), obovoid, compressed, 2-3 mm, 3-5-nerved, faces strigillose; pappi white, 4-6.5 mm. 2n = 16.

Flowering Aug-Sep. Stream banks near hot mineral springs; of conservation concern; ± 1000 m; N.W.T.

Symphyotrichum nahanniense is known only from the South Nahanni River (Mackenzie Mountains), Nahanni National Park.