Aster L.
Perennial herbs, rarely annuals or shrubs. Lvs alternate or all basal, simple, entire to toothed, rarely more deeply incised. Capitula 1-numerous, mostly in cymes or panicles. Involucral bracts in 2-several rows, equal or imbricate, usually herbaceous toward apices, sometimes wholly herbaceous or chartaceous. Receptacle flat or convex; scales 0. Outer florets usually ♀, rarely sterile, usually ligulate, very rarely filiform, few to numerous in 1-2 rows; ligules white to red, purple or blue. Inner florets ⚥, tubular, few to numerous. Achenes all similar, obovoid to cylindric, compressed, glabrous or hairy and sometimes glandular, often 4-5-ribbed; pappus of scabrid hairs in 1 row, sometimes with an outer row of short hairs or scales.
Key
c. 250 spp., cosmopolitan but mainly N. temperate. Naturalised spp. 4 and 1 hybrid group.
This large genus includes many spp. which are grown as ornamentals. There are considerable taxonomic problems at both sp. and generic level with segregate genera accepted by many authors. Semple, J. C. and Brouillet, L., Amer. J. Bot. 67 : 1010-1026 (1980), provided a revised scheme for subgenera and sections, accepted the genus Lasellea as distinct and referred A. novae-angliae to it. Aster is treated here in the broad sense as accepted by most N. Hemisphere Floras.
