Helianthus decapetalus
Helianthus grosseserratus
hélianthe à dix rayons, thin-leaf sunflower
hélianthe à grosses dents, saw-tooth sunflower
erect, glabrous.
erect, glabrous proximally, distally glabrate, scabrellous, or strigillose (glaucous).
cauline; opposite (proximal or all) or alternate (distal);
petioles (1–)2–5 cm;
blades (green, 3-nerved distal to bases) lanceolate to ovate, 7–21 × 4–10 cm, bases rounded to cuneate (often shortly decurrent onto petioles), margins usually serrate (moderately to notably in larger leaves), abaxial faces ± scabro-hispidulous, relatively sparsely gland-dotted.
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.
2–12 cm (not gland-dotted).
0.3–10 cm.
8–12;
laminae 20–25 mm.
14–20;
laminae 23–40 mm.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
100+;
corollas 5–6 mm, lobes yellow;
anthers dark brown to black, appendages yellow.
20–25 (often reflexed), lance-linear to lanceolate, 11–16 × 2–3 mm (sometimes leaflike, longest surpassing discs by 1/2+ their lengths), (margins ciliate) apices attenuate, abaxial faces strigillose to glabrate, not gland-dotted.
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.
3–6(–10).
3–15+.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
3–4 mm, glabrate;
pappi of 2 aristate scales 1.9–2.5 mm.
-lucres hemispheric, 12–25 mm diam.
-lucres broadly hemispheric, 15–25 mm diam.
8–10 mm, 3-toothed.
7–8 mm, entire or 3-toothed (apices acuminate, ± hairy).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus grosseserratus
Helianthus decapetalus is sometimes confused with Heliopsis helianthoides because of shared habitats and superficial similarities. The tetraploid cytotype of H. decapetalus intergrades (and apparently hybridizes) with H. strumosus, particularly in the southern Appalachians; individual specimens can be difficult to place in one or the other species. In addition to morphologic differences, H. decapetalus usually occurs in more mesic habitats, particularly along watercourses; H. strumosus is found in drier sites such as roadside slopes. Helianthus ×multiflorus Linnaeus is a sterile hybrid, often with “doubled” heads (in which disc florets are replaced by ray florets); it is cultivated and is sometimes included within H. decapetalus, e.g., H. decapetalus var. multiflorus (Linnaeus) A. Gray; its parents are H. decapetalus and H. annuus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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