Plants 50-200+ cm; basal offshoots, rhizomes, and stolons absent. Stems erect. Leaf blades linear-lanceolate to narrowly lanceolate; cauline 64-155 × 8-26 mm, bases decurrent. Heads in corymbiform to corymbo-paniculiform arrays; bracts 11-125 × 1-19 mm. Peduncles 3-53 mm; bracts 0-1(-3), linear to oblanceolate, 3-5(-9) mm. Involucres 3.2-4.3 × 8-9 mm. Phyllaries in 3-5 series, oblong to spatulate, subequal, apices acuminate to cuspidate, 0-1 merging down peduncles; outer 2.3-3.9 × 0.5-1 mm; inner 3-4 × 0.6-1 mm. Ray florets 45-60; corollas white to lilac, laminae 9-14 mm, tubes 0.6-1.1 mm. Disc florets 230-400+; corollas 1.8-2.4 mm. Cypselae obovoid to obcordiform, 1.5-2.6 × 1.1-1.9 mm, wings 0.3-0.4 mm wide; pappus awns 0.8-1.75 mm. 2n = 18. Flowering Aug-Sep. Open alluvial soils in wet prairies, shallow marshes, open river creek and lake shores; of conservation concern; 100-200 m; Ill., Mo. Boltonia decurrens is known only from the flood plains of the Illinois and Mississippi rivers. Present-day populations are isolated and restricted to disturbed alluvial habitats, old fields, roadsides, and disturbed wet lake shores that replaced its natural habitats of flooded lake shores and marshes. It is in the Center for Plant Conservation´s National Collection of Endangered Plants.
Similar to B. asteroides var. recognita, but with broader and more numerous lvs, those of the stem conspicuously decurrent; rhizomes wanting; invol bracts subequal or only slightly imbricate; disk-fls numerous, ca 250-400; pappus-awns of the disk apparently always well developed. Flood plains along major rivers; Mo. and Ill.; now rare. Sept., Oct.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.