Helianthus decapetalus
Helianthus longifolius
hélianthe à dix rayons, thin-leaf sunflower
longleaf sunflower
erect, glabrous.
(green or purplish) erect, glabrous.
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.
mostly basal; opposite;
petioles 0–1 cm;
blades linear to narrowly obovate, 13–30 × 0.7–2 cm, bases cuneate, margins entire or obscurely serrate, faces glabrous, not gland-dotted (cauline smaller).
2–12 cm (not gland-dotted).
4–11 cm.
hemispheric, 8–12 mm diam.
8–12;
laminae 20–25 mm.
8–13;
laminae 10–19 mm (abaxial faces not gland-dotted).
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
35+;
corollas 4.2–5.5 mm, lobes yellow;
anthers dark, appendages dark.
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.
18–23, linear-linear, 5–11 × 1–2.5 mm, (margins ciliolate) apices ± attenuate, abaxial faces glabrate or glabrous.
3–6(–10).
3–12.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
2–3 mm, glabrate;
pappi of 2 aristate scales 1.4–2.5 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
6–8 mm, weakly 3-toothed (apices hairy).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus longifolius
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 longifolius is locally escaped from a planting in one county in North Carolina. It is locally abundant where it occurs. It is not similar to or closely related to any other species; natural hybrids of H. longifolius with H. atrorubens and H. occidentalis are known.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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