Helianthus atrorubens
Helianthus divaricatus
purpledisc sunflower, purpledisk sunflower
woodland sunflower
erect, proximally villous to strigoso-hispid, distally hispid or glabrate.
erect, usually glabrous, rarely ± hairy (often glaucous).
mostly basal; opposite;
petioles 4–25 cm (usually winged at least 1/2 their lengths);
blades lanceolate to ovate, 7–26 × 3–10 cm, bases broadly cuneate to nearly truncate (often decurrent onto petioles), margins serrate to crenate, abaxial faces strigoso-hispid (hairs of midribs1+ mm), not gland-dotted (cauline to 8 pairs proximal to heads, ovate to elliptic, smaller).
cauline; opposite;
sessile;
blades (light to dark green, sometimes whitish abaxially, 3-nerved at bases) lanceolate to lance-ovate, 6–15 × 1–5 cm, bases rounded to cordate, margins subentire to serrate, abaxial faces sparsely hispid to hispidulous, gland-dotted.
0.3–17 cm.
0.5–9 cm.
broadly hemispheric, 9–16 mm diam.
hemispheric, 10–15 mm diam.
10–15;
laminae 15–22 mm (abaxial faces not gland-dotted).
8–12;
laminae 15–30 mm.
75+;
corollas 4–6 mm, lobes reddish;
anthers dark, appendages dark (style branches yellow).
40+;
corollas 4.2–5.5 mm, lobes yellow;
anthers usually dark brown to black, appendages yellow.
15–22, broadly ovate to oblong, 7–9 × 4–5 mm, (margins ciliolate) apices obtuse to acute, sometimes mucronate, abaxial faces usually glabrous.
18–25, lanceolate, lance-linear, or lance-ovate, 6–12 × 2–2.5 mm, (margins ciliate) apices acuminate to attenuate, abaxial faces hispidulous to glabrate, not gland-dotted.
(1–)3–15+.
1–10.
2.8–3 mm, glabrous or distally puberulent;
pappi of 2 aristate scales 2.5–2.8 mm.
3–3.6 mm, glabrate;
pappi of 2 aristate scales 2.2–2.5 mm.
4–5.5 mm, ± 3-toothed to entire.
5–8 mm, 3-toothed (apices ciliate).
= 34.
= 34.
Helianthus atrorubens
Helianthus divaricatus
Helianthus atrorubens and H. silphioides form a morphologically similar pair of species that share the distinctive feature of relatively broad, tightly appressed phyllaries with apices obtuse to acute. Helianthus atrorubens has a more easterly geographic distribution along the Piedmont and the Atlantic coastal plain and the southern Appalachian Mountains; distribution of H. silphioides is centered in the Ozark region. In general, H. silphioides differs in its usually well developed cauline leaves, and basal leaves with winged petioles that are less than half the total lengths. Involucres with phyllaries tightly appressed are also observed in H. occidentalis and H. pauciflorus subsp. pauciflorus, which differs in having the phyllary apices acute to acuminate as well as in usually having abaxial faces of leaves and ray laminae densely gland-dotted.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
One of the earlier flowering perennial Helianthus, H. divaricatus resembles the tetraploid H. hirsutus but differs by its usually glabrous and often glaucous stems, sessile or subsessile leaves, and smaller reproductive organs (disc corollas, paleae, cypselae). Plants from the Ozark region of Arkansas have larger leaves and heads and may represent a polyploid form of H. divaricatus. Natural hybrids with H. microcephalus have been named H. glaucus Small (D. M. Smith and A. T. Guard 1958). Hybrids with other species differ from H. divaricatus in having short but distinct petioles, hairy stems, leaves with more rounded bases, and primary lateral leaf veins diverging in a subopposite manner distal to bases, rather than being strictly opposite and basal.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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