Helianthus decapetalus
Helianthus petiolaris
hélianthe à dix rayons, thin-leaf sunflower
prairie sunflower, unknown
erect, glabrous.
erect, usually densely canescent, hispid, or strigillose, rarely ± hirsute or glabrate.
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 2–4 cm;
blades (often bluish green) lanceolate to deltate-ovate or ovate, 4–15 × 1–8 cm, bases subcordate or truncate to cuneate, margins entire or ± serrate, abaxial faces strigose, sparsely to densely, or not at all, gland-dotted.
2–12 cm (not gland-dotted).
4–15(–40) cm.
± hemispheric, 10–24 mm diam.
8–12;
laminae 20–25 mm.
10–30;
laminae 15–20 mm.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
50–100+;
corollas 4.5–6 mm, lobes usually reddish, rarely yellow;
anthers reddish to purplish, appendages purplish (style branches reddish).
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.
14–25, lance-linear to lanceolate to lance-ovate, 10–14 × 1–4(–5) mm, (margins sometimes ciliate) apices short-attenuate, abaxial faces usually hispidulous, rarely sparsely hirsute to glabrate.
3–6(–10).
1–5.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
3–4.5 mm, ± villous;
pappi of 2 aristate scales 1.5–3 mm plus 0–2 erose scales 0.3–0.5 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
4.5–7.5 mm, 3-toothed, middle teeth ± ciliate or bearded, hairs whitish, 0.5–0.7 mm.
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus petiolaris
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.)
Subspecies 2 (2 in the flora).
Helianthus petiolaris is adventive beyond western North America.
A third subspecies has yet to be named at that rank in Helianthus petiolaris; it has been called H. petiolaris var. canescens A. Gray. It differs in having stems, leaves, and phyllaries densely canescent and abaxial faces of leaves densely gland-dotted. It is additionally characterized by peduncles usually ebracteate, phyllaries 1–2 mm wide, disc corolla throats gradually narrowed distal to slight, not densely hairy basal bulges, and 2n = 34. It flowers late spring through late summer and grows on sandy soils in open areas at (10–)1000–2300 m in Arizona, California, Nevada, New Mexico, and Texas and in Mexico. It was treated as H. niveus (Bentham) Brandegee subsp. canescens (A. Gray) Heiser by C. B. Heiser et al. (1969); molecular and morphologic data appear to favor a placement within H. petiolaris.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Stems usually hispidulous to strigillose; peduncles usually bractless; phyllaries 3–5 mm wide; disc corollas: throats abruptly narrowed distal to densely hairy basal bulbs | subsp. petiolaris |
1. Stems usually ± hispid; peduncles usually each with leafy bract subtending head; phyllaries 2–3.5 mm wide; disc corollas: throats gradually narrowed distal to slight, not densely hairy, basal bulges | subsp. fallax |
MD Biodiversity- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
Go Botany, 
IL Wildflowers, 
KS Wildflowers, 
LA Plants, 
MI Flora, 
MN Wildflowers, 
MO Plants, 
PNW Herbaria 
WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
