Helianthus decapetalus
Helianthus maximiliani
hélianthe à dix rayons, thin-leaf sunflower
hélianthe de maximilien, Maximilian sunflower, Maximilian's sunflower
erect, glabrous.
erect, 5–30 dm, scabrous to scabro-hispidulous.
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; mostly alternate;
petioles 0–2 cm;
blades (light green to gray-green, 1-nerved, conduplicate) lanceolate, 10–30 × 2–5.5 cm, bases cuneate, margins usually entire, sometimes serrulate, abaxial faces scabrous to scabro-hispid, gland-dotted.
2–12 cm (not gland-dotted).
1–11 cm.
hemispheric, 13–28 mm diam.
8–12;
laminae 20–25 mm.
10–25;
laminae (15–)25–40 mm.
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 5–7 mm, lobes yellow;
anthers dark brown or black;
appendages usually yellow, sometimes partly 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.
30–40, lanceolate, 14–20 × 2–3 mm, (margins ciliate) apices acute to attenuate, abaxial faces canescent, gland-dotted.
3–6(–10).
(1–)3–15 (often in racemiform to spiciform arrays).
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
3–4 mm, glabrate;
pappi of 2 aristate scales 3–4.1 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
7–11 mm, entire or 3-toothed (apices greenish, mucronate, hairy).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus maximiliani
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 maximiliani is introduced in eastern Ontario and in Quebec. It appears to be native to midcontinental prairie regions and has spread along railroads and highways into all areas of North America. Its wide dispersal may be aided by cultivation for its attractive, showy floral displays. In addition to the usually conduplicate, single-nerved leaves and spikelike arrangement of the heads, it is distinguished by the whitish-canescent indument of the leaves and stems and the long-attenuate phyllaries.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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