Plants 30-150 cm. Stems simple or branched basally. Heads 30-100 in open, diffuse arrays, secund on primary branches longer than peduncles. Involucres 5-7(-8) mm. Phyllaries 18-24(-30), subulate to lanceolate (often broadly so), green zones broadly lanceolate, absent from proximal portion. Ray florets 21-28(-38) in (2-)3 series; laminae white (drying white or lavender), 1.3-1.7(-2) × 0.2-0.3 mm, shorter than pappi, drying in inward curls, rarely coiling. Disc florets (3-)7-14, 4-4.9 mm. Cypselae 1.5-2.6(-3) mm; pappi 4-5.1(-5.3) mm. 2n = 20. Flowering Jul-Nov. Salt marshes, brackish marshes; 0-10 m; introduced; Ala., Fla., La., N.C., Tex.; Bermuda; South America; introduced in Europe (France), Asia (Iraq, Japan), Australia, and elsewhere. The name Astersubulatus Michaux var. sandwicensis (A. Gray ex H. Mann) A. G. Jones (Brinttonia 36: 465. 1984) has priority at the varietal level; the combination in Symphyotrichum has yet to be made.