Helianthus decapetalus
Helianthus angustifolius
hélianthe à dix rayons, thin-leaf sunflower
swamp sneezeweed, swamp sunflower
erect, glabrous.
erect, usually ± hairy.
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 cauline; opposite or alternate;
sessile or subsessile;
blades (3-nerved near bases) narrowly lanceolate to linear, 8–15 × 0.15–0.5(–1) cm, bases cuneate, margins entire (revolute, abaxial face sometimes obscured by rolled margins), abaxial faces strigose to hispid or hirsute, sometimes (adaxial not) gland-dotted.
2–12 cm (not gland-dotted).
5–15 cm.
shallowly hemispheric, 10–20 mm diam.
8–12;
laminae 20–25 mm.
10–20;
laminae 10–20 mm (abaxial faces 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.
75+;
corollas 4–4.5 mm, lobes yellow;
anthers dark brown or black, appendages dark (style branches usually 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.
25–32 (loose), lanceolate, 4–9 × 1–2 mm, apices acute to slightly acuminate, abaxial faces usually scabrous, rarely glabrous, usually gland-dotted.
3–6(–10).
3–16.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
2–3 mm, glabrate;
pappi of 2 aristate scales 1.5–2.1 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
(oblanceolate) 5.5–6.5 mm, entire or ± 3-toothed (apices purplish, mucronate, gland-dotted).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus angustifolius
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.)
The distal parts of Helianthus angustifolius are identical in appearance to those of H. simulans; plants of the latter are taller (200+ cm) and more robust. The leaves are not only narrower in H. angustifolius but also tend to be more strongly revolute (abaxial faces sometimes scarcely visible).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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