Perennials, 100–400 cm (rhizomatous). Stems (usually reddish) erect, hairy. Leaves cauline; mostly alternate; petioles 0–1.2 cm (ciliate); blades (3-nerved from bases) lanceolate to lanceovate, 7–20 × 1.2–3.5 cm, bases cuneate, margins serrulate to subentire (± flat), abaxial faces scabrous or ± hirsute, sometimes glanddotted. Heads 1–12. Peduncles 8–12 mm. Involucres hemispheric, 10–24 mm diam. Phyllaries 20–25 (loose or spreading), linear, 8–15 × 1.2–2 mm, (margins usually ciliate) apices acute to attenuate, abaxial faces sparsely strigose, not glanddotted. Paleae 7–9 mm, entire or ± 3-toothed (apices acute, hairy). Ray-florets 12–20; laminae (often pale-yellow) 15–25 mm (abaxial faces not glanddotted). Disc-florets 60+; corollas 5–6 mm, lobes yellow; anthers dark-brown or black, appendages dark. Cypselae 3–4 mm, glabrate; pappi of 2 aristate scales 2.4–3 mm. 2n = 34.

Phenology: Flowering late summer–fall.
Habitat: Usually wet, open sites
Elevation: 10–600+ m

Distribution

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N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Miss., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Vt., Va., W.Va., Wis.

Discussion

Helianthus giganteus was probably introduced in Newfoundland. It intergrades with H. nuttallii and H. grosseserratus; it is distinctive in its hairy, reddish-colored stems, dark anther appendages, and prominent setae on the petioles. The natural hybrid of H. giganteus with H. grosseserratus has been called H. luxurians E. Watson (R. W. Long 1954). Hybrids of H. giganteus with H. divaricatus have been referred to as H. ambiguus (Torrey & A. Gray) Britton and H. ×divariserratus R. W. Long (Long 1954).

Selected References

None.

Lower Taxa

None.