Plants 40-120 cm; in clones; rhizomes elongate, strong. Stems 1, erect, strict (slightly flexuous distally), simple, glabrous, distally ± villosulous (arrays). Leaves cauline; proximal withering by flowering, narrowly winged-petiolate, blades broadly oblanceolate or elliptic to obovate, smaller than mid; mid and distal winged-petiolate (5-30 mm), broadly elliptic to oblanceolate, (70-)90-140 × 40-50(-60) mm, reduced distally, bases cuneate, with 4-5 pairs of marked veins, margins coarsely serrate (teeth 1-4 mm), slightly revolute, scabrous, apices acuminate; abaxial faces glabrescent, adaxial sparsely pilose, mainly on veins. Heads 1-10, borne singly or in corymbiform arrays. Peduncles sparsely pilose; bracts 0-1, foliaceous, remotely serrulate. Involucres campanulate, 7-11 mm, shorter than pappi. Phyllaries 32-36 in 4-5 series, broadly oblong, strongly unequal, scarious, dark green zones wide, from ¹ / 2 distally, margins hyaline, narrow, erose, densely ciliate, apices appressed or often slightly squarrose, obtuse to subacute, faces glabrous, eglandular. Ray florets 10-30; corollas pale white to pale blue, 10-15 × 1.5-2 mm. Disc florets 10-20; corollas yellow turning pinkish, ca. 4.5-5 mm, tubes longer than funnelform throats, lobes spreading, triangular, ca. 1.5 mm. Cypselae tan, fusiform, cylindric, 5-6 mm, ribs 7-11, stramineous, faces ± strigose; pappi of pale stramineous (clavate) bristles 5-7 mm, shorter than to ± equaling disc corollas. 2n = 54.

Flowering late summer-fall. Back edge of spring-flooded, summer-dry, sandstone boulder-cobble river bars with shrubby vegetation; of conservation concern; (600-)1000-1500 m; Ky., Tenn.

Eurybia saxicastelli is known only from the Rockcastle River of Kentucky (J. J. N. Campbell and M. E. Medley 1989) and Tennessee.