Colonial by long rhizomes; stems 4-15 dm, glabrous or ±puberulent in lines; lvs all cauline, glabrous, or slightly scabrous above, linear to narrowly lanceolate, acute, tapering to the sessile base, entire or slightly toothed, to 11 נ1 cm, those of the branches becoming much reduced; heads mostly numerous in an open, ample infl with long, divaricate, divergently bracteate, often recurved branches that tend to be secund, the shortly bracteate peduncles short or to 1.5 cm; invol 2.5-3.5(-4) mm, glabrous, its bracts imbricate, with mostly elongate green tip; rays 15-30, white or seldom purplish, 3-6 mm; lobes of the disk-cors comprising ca 40% of the limb. Mostly in moist, open places, and in floodplain-forests; Me. to Fla. and La., chiefly near the coast, and upstream along river-bottoms in the Mississippi R. drainage to w. Tenn., s. O., and w. Mo. (A. brachypholis; A. fragilis, misapplied, the type at B! probably a garden hybrid of A. lanceolatus and some other sp. such as A. dumosus; A. vimineus Lam., misapplied, the type at P! better referred to A. lateriflorus or a hybrid derivative thereof)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.