Perennials, 15-40(-60) cm, colonial; thinly long-rhizomatous. Stems 1, erect (straight), hirsute to hispido-hirsute, hirsutulous distally. Leaves: margins shallowly crenate to serrate-crenate, abaxial faces strigillose, adaxial scabrous; basal withering by flowering, petiolate, petioles winged, clasping to subclasping, shallowly auriculate, blades subspatulate or oblanceolate-elliptic, 30-70 × 10-15 mm, bases attenuate to cuneate, apices acute; proximal cauline withering by flowering, widely winged-petiolate, blades oblanceolate-elliptic, 50-110 × 8-22 mm, bases attenuate, apices acute; distal subsessile, blades oblong-lanceolate, 10-30 × 4-6(-8) mm. Heads in broad, cylindro-paniculiform arrays, branches ascending. Peduncles 0.5-1.5(-3) cm, bracts foliaceous. Involucres turbino-campanulate, 6-11 wide mm. Phyllaries in 3-4 series, slightly unequal, narrowly oblong-lanceolate, bases indurate ¹ / 2 - ² / 3 , margins not scarious, irregularly ciliolate, green zones rhombic-lanceolate, apices acute to acuminate, faces glabrous or distally strigoso-puberulent. Ray florets 18-32; corollas blue to lavender, laminae 6-9 × 0.8-1.4 mm. Disc florets [number unknown]; corollas yellow, at least lobes becoming purple, (4-)4.5-5.5 mm, tubes shorter than cylindro-funnelform limbs, lobes triangular, 0.8-1 mm. Cypselae tan to often purplish, oblong to oblanceoloid, ± compressed, 2.6-3 mm, 4-6-nerved, faces sparsely strigillose; pappi white, [length unknown] mm.

Flowering Sep-Oct(-Nov). Ultramafic outcrop barrens, in Quercus alba-Pinus rigida-Sporobolus heterolepis-Andropogon gerardii woodlands and grass-dominated areas; of conservation concern; 900-1300 m; N.C.

Symphyotrichum rhiannon is known only from a southern Appalachian high-elevation outcrop barren around Buck Creek, southern Nantahala Mountains, Clay County.