Perennials [subshrubs, shrubs], 3-300 cm (rhizomatous, rhizomes long or short, plants sometimes with branched caudices). Stems ascending to erect, simple, ± densely hairy [glabrous], sometimes stipitate-glandular. Leaves basal and/or cauline; sessile or petiolate; blades 1-nerved, spatulate, obovate (mainly basal), oblanceolate, lance-oblong, lanceolate, or linear, distal often reduced, margins entire or serrate [lobed], faces hairy. Heads radiate, borne singly or in corymbiform [paniculiform] arrays. Involucres broadly campanulate or hemispheric [cylindro-campanulate], 15-25 mm diam. Phyllaries persistent, 25-50 in 2-4 series, 1-nerved (flat), ovate to lanceolate, unequal to subequal, bases ± scarious, herbaceous distally or not, green zones along midnerves, margins scarious to hyaline, densely villous, strigillose, or glabrous, sometimes ± short-stipitate-glandular. Receptacles flat or convex, pitted, epaleate. Ray florets 14-55(-100)[-150] in 1 series, pistillate, fertile; corollas white, pink, purple, blue, or violet. Disc florets 20-100+, bisexual, fertile; corollas usually yellow (sometimes reddening), slightly ampliate [tubular], tubes shorter than to equaling funnelform or campanulate throats, lobes 5, usually erect to spreading, rarely reflexed, lanceolate; style-branch appendages lanceolate. Cypselae obconic, compressed, 2 marginal ribs, faces ± densely strigillose [glabrous], sometimes short-stipitate-glandular; pappi persistent, of 20-30 white to tawny, ± equal, barbellate, apically usually attenuate, sometimes ± clavate bristles in 1-2 series. x = 9. Some species of Aster are cultivated and sold in the horticultural trade (J. C. Semple et al. 2002). Some species, notably the type of the genus, Aster amellus Linnaeus, have a large number of cultivars. The genus name is the type of the family name Asteraceae. As circumscribed here, Aster excludes members of the Crinitaria-Galatella-Tripolium complex, which are closer to the Bellidinae ( Bellis, Bellium, Bellidiastrum; O. Fiz et al. 2002). Analysis of molecular data shows that Aster in the strict sense includes Diplactis, Kalimeris, Heteropappus, and a few other eastern Asiatic segregates. The relationship of Aster in the strict sense to other Astereae genera is unclear, and the delimitation of subtribe Asterinae in the sense of G. L. Nesom (1994b) is still uncertain.