Plants 30-120(-150) cm. Stems simple. Heads (10-)30-100(-150), in elongate, pyramidal, much branched arrays. Involucres (5-) 6-7(-8.2) mm. Phyllaries 20-30, subulate to lanceolate, narrow, green zones narrowly to broadly lanceolate, extending phyllary length. Ray florets 16-30 in 2 series; laminae white (drying white or lavender), (1.3-)1.5-2.6(-3.1) × 0.2-0.5 mm, shorter to slightly longer than pappi, drying in 0-1 coil (apices often deeply lobed). Disc florets 4-10(-13); corollas 3.8-4.6(-4.9) mm. Cypselae (1.2-)1.5-2.5 mm; pappi (3.5-)4-5.5 mm. 2n = 10.

Flowering midsummer-autumn(-winter). Salt marshes, brackish marshes, tidal marshes, salted highways; 0 (100-300 inland) m; N.B., Ont.; Ala., Ark., Conn., Del., Fla., Ga., Ill., Ind., La., Maine, Md., Mass., Mich., Miss., Nebr., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tex., Va.; introduced in Asia, Africa.

Variety subulatum is disjunct in northern New Brunswick. It is apparently introduced around salt mines and other salted habitats in Ontario, Michigan, and Ohio.