Perennials, 100-400(-500) cm (rhi-zomatous). Stems erect, glabrous proximally, distally glabrate, scabrellous, or strigillose (glaucous). Leaves cauline; opposite (proximal) or alternate; petioles (1-)2-5 cm; blades (light to dark green, 3-nerved distal to bases) lanceolate to lance-ovate, 10-32 × (1.2-)4-9 cm, bases cuneate, margins usually coarsely to shallowly serrate, rarely subentire (flat), abaxial faces puberulent to tomentulose, gland-dotted. Heads 3-15+. Peduncles 0.3-10 cm. Invo-lucres broadly hemispheric, 15-25 mm diam. Phyllaries 25-30 (loose, spreading ), lance-linear, 10-14 × 1.5-2.5 mm (subequal), (margins ± ciliate) apices attenuate, abaxial faces glabrous or puberulent, not gland-dotted. Paleae 7-8 mm, entire or 3-toothed (apices acuminate, ± hairy). Ray florets 14-20; laminae 23-40 mm. Disc florets 100+; corollas 5-6 mm, lobes yellow; anthers dark brown to black, appendages yellow. Cypselae 3-4 mm, glabrate; pappi of 2 aristate scales 1.9-2.5 mm. 2n = 34. Flowering late summer-fall. Dry to wet prairies, other open sites; 10-300+ m; Ont., Que.; Ark., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., S.Dak., Tenn., Tex., Va., Wash., W.Va., Wis. Helianthus grosseserratus is native to midwestern North America and has spread as a roadside weed into other areas, such as New England and the southeastern United States. It is introduced in Canada. Hybrids between H. maximiliani and H. grosseserratus are known as H. ×intermedius R. W. Long (R. W. Long 1954; Long 1966). Hybrids of H. grosseserratus with H. salicifolius have been described as H. kellermannii Britton (Long 1955), and those with H. mollis as H. brevifolius E. Watson (R. C. Jackson and A. T. Guard 1957b).
From Flora of Indiana (1940) by Charles C. Deam
This sunflower prefers the moist, black, sandy soil of prairie habitats and is frequent in them in the western part of the state. It grows also in moist, hard, white clay soil in the western part of the Illinoian drift with other typical prairie plants. It is now found mostly along dredged ditches, roadside ditches, and streams and in low woods.
Indiana Coefficient of Conservatism: C = 3
Wetland Indicator Status: FACW
Diagnostic Traits: plants to 5 m; stems glabrous; leaves opposite below, alternate above middle, mostly <3 cm wide, serrate or denticulate, finely to densely pubescent beneath; petiole 1-4 cm; phyllaries lance-linear, slightly ciliate.
Coarsely fibrous-rooted, rhizomatous perennial; stems 1-4 m, strigose in the infl, otherwise glabrous and often glaucous; lvs lanceolate, 10-20 נ1.5-4 cm (or the lower larger), acuminate, tapering to an often winged petiole 1-4 cm, sharply toothed to sometimes subentire, strigose on both sides, or more hirtellous or puberulent especially on the paler lower surface, usually slightly trinerved at base, the middle and upper commonly alternate; disk yellow, 1.5-2.5 cm wide; invol bracts lance-linear, loose, attenuate, surpassing the disk, ±ciliate, at least near the base, and sometimes short-hairy on the back; rays 10-20, 2-4.5 cm; 2n=34. Bottomlands, damp prairies, and other moist places; Me. to Minn., s. to Ga. and Tex., perhaps only intr. e. of O. July-Oct. A. hybrid with H. salicifolius has been called H. ثellermanii Britton.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.