Helianthus decapetalus
Helianthus exilis
hélianthe à dix rayons, thin-leaf sunflower
serpentine sunflower
erect, glabrous.
(often reddish) erect, 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; mostly alternate;
petioles 0.7–2.5 cm;
blades lance-linear to lance-ovate or ovate, 3–15 × 0.5–3 cm, bases cuneate, margins usually entire or shallowly serrate, abaxial faces gland-dotted.
2–12 cm (not gland-dotted).
(1–)3–13(–20) cm.
hemispheric, 15–20 mm diam.
8–12;
laminae 20–25 mm.
10–13;
laminae 14–20 mm.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
50+;
corollas 4–6 mm, lobes reddish;
anthers reddish purple, appendages usually purplish (style branches reddish or 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.
12–17, lanceolate, 8–17 × 3–4 mm, apices narrowed gradually, abaxial faces hirsute.
3–6(–10).
1–7.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
(2.5–)3–3.5(–4) mm, glabrate;
pappi of 2 lanceolate scales 1.7–2.7 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
9.5–10 mm, 3-toothed (middle teeth surpassing discs, apices greenish or yellow-brown, glabrous).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus exilis
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 exilis is very similar morphologically to H. bolanderi and is often included in it; there are discrete differences between the two for fatty acid composition (C. E. Rogers et al. 1982) as well as some molecular markers (L. H. Rieseberg et al. 1988). It is listed as of concern by the California Native Plant Society.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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