Helianthus decapetalus
Helianthus schweinitzii
hélianthe à dix rayons, thin-leaf sunflower
Schweinitz's sunflower
erect, glabrous.
(often reddish, leafy) erect, ± strigose proximally, strigose or glabrous distally.
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 0–1 cm;
blades (light to dark green, 3-nerved distal to bases) lanceolate to lance-linear, 6–18 × 1–2 cm, bases cuneate, margins entire or subentire (revolute), faces hirsute to tomentose and gland-dotted (abaxial) or scabrous (adaxial).
2–12 cm (not gland-dotted).
1.5–8 cm (not gland-dotted).
hemispheric, 9–10(–16) mm diam.
8–12;
laminae 20–25 mm.
8–15;
laminae 15–22 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.
40+;
corollas 5–6 mm, lobes yellow;
anthers dark brown to black, appendages dark or reddish brown.
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.
16–20 (reflexed or loose), lanceolate or lance-ovate, 5–7 × 1.5–2.3 mm, apices acute to acuminate, abaxial faces hirsute (proximally) to glabrate, gland-dotted.
3–6(–10).
3–6.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
3–4 mm, glabrate;
pappi of 2 aristate scales 1.5–2 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
5.5–6.5 mm, 3-toothed (apices hairy).
= 34, 68.
= 68.
Helianthus decapetalus
Helianthus schweinitzii
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.)
Of conservation concern.
Helianthus schweinitzii is distinguished by its relatively small heads and sessile to subsessile, narrowly lanceolate leaves with revolute margins. Chromosome number, typification issues, and identification of voucher specimens were updated by J. F. Matthews et al. (1997).
Helianthus schweinitzii is found on the Carolina piedmont. It was listed as endangered in the Federal Register on May 7, 1991, and is known from 16 populations. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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