Perennials, 15-120 cm (rhizomatous or with stout, branching, woody caudices). Stems erect, simple, glabrate to hairy. Leaves basal (in rosettes, usually withering by flowering) and cauline; alternate; petiolate (basal) to sessile (cauline); basal blades spatulate, margins distally serrate; cauline blades 1-nerved (reticulately nerved), linear, obovate or ovate, reduced distally, margins serrate or entire, ciliate (apices acuminate to acute, sometime slightly cuspidate), faces glabrate or hairy. Heads radiate, (2-5 per branch in clusters) in corymbiform to broadly corymbiform (sometimes compact) arrays. Involucres cylindric, (3-9 ×) 2.4-8.5 mm. Phyllaries 15-30 in 3-5 series, 1-nerved (± keeled), thumbnail-shaped, inner more linear, unequal, bases ± indurate, margins scarious, ciliate, apices with dark green zones, (faces glabrate to hairy). Receptacles slightly convex, pitted, epaleate. Ray florets 1-6, pistillate, fertile; corollas white. Disc florets 5-19, bisexual, fertile; corollas white to cream, tubes shorter (longer in S. linifolius) than weakly funnelform throats, lobes 5, erect to spreading, triangular; style-branch appendages linear-lanceolate. Cypselae fusiform to obconic, terete to slightly compressed, 7-10-ribbed, ± densely strigose; pappi persistent, of 25-50, white to tan or rust , barbellate bristles in (2-)3(-4) series (outermost, when present, 0.1-1 mm, outer distally attenuate, 3-7 mm, inner distally clavate, 3-8 mm). x = 9. Gray et al. [1878-1897, vol. 1(2)], J. K. Small (1903), M. L. Fernald (1950), and L. Abrams and R. S. Ferris (1923-1960, vol. 4) considered Sericocarpus as a genus distinct from the traditionally defined genus Aster. In the last fifty years most botanists, including A. G. Jones (1980) and J. C. Semple and L. Brouillet (1980), followed A. Cronquist (1955, 1980; H. A. Gleason and Cronquist 1963, 1991), who included the species in Aster in the broad traditional sense. Semple et al. (1996) retained Sericocarpus within Aster subg. Aster on the basis of similarities in phyllary traits and the results of a restriction fragment length polymorphism analysis of chloroplast DNA (Xiang C. and Semple 1996). DNA sequence data conclusively show that Sericocarpus is more closely related to Solidago than to other North American species of asters, which themselves can no longer be placed in the genus Aster (R. Noyes and L. H. Rieseberg 1999; Semple et al. 2002). J. L. A. Hood and J. C. Semple (2003) included observations on the triple pappus of some species of Sericocarpus in their paper on pappus variation in Solidago. They also proposed a 'nomenclature' for the pappus whorls in the Astereae. The triseriate pappus of Sericocarpus is similar to that of Doellingeria and more obviously triple than in species of Solidago. M. J. Blondin et al. (2005) included detailed descriptions of pappus traits for all taxa in their multivariate study of the genus. In the descriptions below, involucre lengths were taken at flowering. Subtending peduncle bracts are those immediately subtending heads.