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.
Heads generally radiate, the rays pistillate and fertile, anthocyanic or white, in a few spp. reduced and inconspicuous or even wanting, the cor of the pistillate fls then a mere slender tube; invol bracts in 2 or more series, equal or more often imbricate, usually ±herbaceous at the tip and chartaceous below, sometimes herbaceous or chartaceous throughout; receptacle naked, flat or a little convex; disk-fls perfect and fertile, red or purple to yellow; style-branches flattened, with mostly narrow and acute or acuminate, externally short-hairy appendage; achenes several-nerved; pappus of numerous capillary bristles, sometimes with an additional short outer series; perennial (seldom annual) herbs, most spp. fibrous-rooted, with simple, alternate, entire or variously toothed lvs and solitary to more often several or numerous, hemispheric to subcylindric heads. (Brachyactis, Doellingeria, Ionactis, Sericocarpus) 175+, mainly N. Amer. Our spp. bloom in mid- or late summer and fall. Hybrids abound; some of the more notable ones are here formally treated. Some of the species with chromosome numbers based on x=8 (especially in the Heterophylli) tend to have additional B-chromosomes, and have often been reported to have numbers based on 9. The disk-cors characteristically consist of a slender (often short) basal tube and a more swollen limb; the lobes are part of the limb. The terms lvs basally disposed and lvs chiefly cauline are here used as explained under Solidago.
The plant traditionally called Aster (or Unamia) ptarmicoides is here referred to Solidago, in spite of its white rays. It hybridizes with several spp. of Solidago (especially of the sect. Oligoneuron), but not with Aster. It is marked by its 10-25 white rays, white disk-cors and copious (but not double) pappus with many of the bristles clavellate- thickened toward the tip.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.