Perennials, 30–200+ cm (rhizomatous, stoloniferous, or with basal offshoots). Stems erect to ascending, branched distally (ribbed), glabrous. Leaves basal (withering by flowering) and cauline; alternate; sessile (sometimes decurrent); blades 1-nerved, linear, subulate to lanceolate or oblanceolate (bases attenuate, cauline sometimes decurrent), margins entire to serrulate (teeth callous-tipped), (apices acute to acuminate) faces glabrous. Heads radiate, (10–100+) in leafy, corymbiform or paniculiform arrays. (Peduncles bracteate or ebracteate, bracts leaflike or scalelike.) Involucres hemispheric, (2–5 ×) 3–14 mm. Phyllaries 30–55 in 3–6 series, 1-nerved (midribs thickened, resinous; flat), linear to oblanceolate or spatulate, unequal to subequal, margins ± membranaceous, faces glabrous. Receptacles conic to hemispheric, obscurely pitted, epaleate. Ray florets 20–60, pistillate, fertile; corollas white to lilac (laminae linear to elliptic). Disc florets 50–400+, bisexual, fertile; corollas yellow, tubes shorter than funnelform throats, lobes 5, erect, triangular; style-branch appendages deltate. Cypselae dimorphic (brownish); ray ± triquetrous, margins arrowly winged, ribs 2 abaxial, 1 adaxial; disc obovoid to cuneate or obcordiform, laterally compressed, margins winged or not, resin ducts present, faces often puberulent; pappi persistent, usually of 2–3 sclerified awns plus (0–)7–12 shorter bristles or scales in 1 series. x = 9.
Species 5 (5 in the flora).
|1||Disc cypselae lacking wings, or if present wings 0.01–0.1 mm wide; pappus awns 0–0.4 mm||> 2|
|1||Disc cypselae wings 0.1–0.5 mm wide; pappus awns (0.3–)0.4–2 mm||> 3|
|2||Heads in corymbiform arrays; outer phyllaries 1.7–2.8 mm; ray laminae 5–13 mm||Boltonia asteroides|
|2||Heads in paniculiform arrays; outer phyllaries 1.2–1.6 mm; ray laminae 3–7.5 mm||Boltonia caroliniana|
|3||Bases of cauline leaves decurrent; rhizomes and stolons absent; Illinois, Missouri||Boltonia decurrens|
|3||Bases of cauline leaves not decurrent; rhizomes or stolons present or absent; widely distributed or not in Illinois or Missouri.||> 4|
|4||Heads in paniculiform arrays, primary branches mostly spreading; only proximal bracts leaflike, 8–55 mm, others reduced and linear to linear-oblanceolate or subulate, 2–10(–15) mm||Boltonia diffusa|
|4||Heads in corymbiform arrays, branches spreading to ascending; most bracts leaflike, 10–120 mm, only peduncle bracts reduced, linear to subulate or ovate to linear-oblanceolate, 1–12(–62) mm||> 5|
|5||Pappus awns 0.3–0.8 mm; outer phyllaries 1.3–2 mm; ray laminae 5–9 mm; Florida panhandle to se Louisiana||Boltonia apalachicolensis|
|5||Pappus awns 0.4–2 mm; outer phyllaries 1.5–3.8 mm; ray laminae 5–13 mm; e North America, Idaho, Oregon||Boltonia asteroides|