Plants 10-100 cm; in lax clones, eglandular; rhizomes elongate or short, filiform or cordlike, herbaceous, remotely scaly. Stems 1, erect, straight, often reddish, simple, glabrous or glabrescent to sparsely villous proximally, villous distally. Leaves cauline, rugose-veined, margins ± revolute, ± remotely, ± deeply serrate, scabrous, teeth ± indurate (mucronate), apices mucronulate, abaxial faces scabrous, adaxial ± villous, particularly on veins (increasingly so distally); proximalmost withering by flowering, winged-petiolate, petioles equaling or longer than blades, bases ± sheathing, sometimes marcescent, blades spatulate to oblanceolate, 10-42 × 3-8 mm, sometimes reduced, smaller than mid, bases attenuate to cuneate, apices obtuse to acute; mid sessile, lanceolate, oblanceolate, or narrowly obovate to narrowly elliptic or elliptic, (23-)30-115 × 5-36 mm, gradually reduced distally, bases tapering or rounded to ± auriculate-clasping (often narrowed above base), apices acute to acuminate; distal (arrays) sessile, (6-)10-40 × 2-7 mm. Heads 1-25+ in open corymbiform arrays or borne singly. Peduncles ± densely villous; bracts 0-2, sometimes subtending heads. Involucres campanulate, 5.5-9 mm, shorter than pappi. Phyllaries 30-50 in 4-5 series, oblong or oblong-lanceolate, seldom ovate (outer), lanceolate to linear-lanceolate (inner), strongly unequal, membranous, bases indurate, rounded (outer), green zones full-width, occasionally purplish (inner), in distal 1 / 2 (outer; rarely 2 / 3 and foliaceous) to less than 1 / 6 and paler or none (inner), margins hyaline (seldom purplish), narrowly scarious, ± erose, densely ciliate, apices usually appressed, often squarrose, usually acute, sometimes obtuse, mucronulate, faces glabrous or sparsely strigillose. Ray florets 13-30; corollas pale blue-violet, 10.5-15 × 1.4-2 mm. Disc florets 37-72; corollas yellow, 4.5-6 mm, slightly ampliate, 4.8-5.8 mm, tube lengths about twice funnelform throats (2.7-3.4 mm), lobes erect, lanceolate, 0.6-1 mm. Cypselae tawny to stramineous, fusiform to cylindro-obconic, slightly compressed, 2.7-3.5 mm, ribs 8-18 (stramineous or reddish brown), ± crowded, faces glabrous; pappi of pale cinnamon bristles 4.5-5.2 mm, shorter than disc corollas. 2n = 18.
Flowering late summer-early fall. Fens, sphagnum bogs, lake and creek shores, edges of or openings in wet spruce or tamarack forests, open boggy woods, ± wet meadows, ditches; 0-600+ m; St. Pierre and Miquelon; N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que.; Conn., Del., D.C., Ky., Maine, Md., Mass., N.H., N.J., N.Y., Pa., R.I., Vt., Va., W.Va.
Eurybia radula reaches its northwestern limit south of James Bay in northeastern Ontario, where it is rare (J. C. Semple et al. 2002). It is vulnerable in most of its United States range. Aster radula var. strictus (Pursh) A. Gray (for which no combination exists in Eurybia) appears to be a reduced, more slender plant with 1-8 heads (M. L. Fernald 1950) from more northern parts of the range (Newfoundland and Labrador, northern Quebec, northern Nova Scotia), presumably due to harsher conditions; an entire spectrum of intermediates appears to exist with the typical variety to the south, however, and it is unclear whether the variety should be recognized. It seems that the common name, rough aster, stems from a misinterpretation of the Latin epithet radula, which means scraper (rough would be radulans).