Helianthus atrorubens
Helianthus arizonensis
purpledisc sunflower, purpledisk sunflower
Arizona sunflower
erect, proximally villous to strigoso-hispid, distally hispid or glabrate.
erect to ascending, glabrous (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 (bluish green) lanceolate, 2–7 × 0.5–1.3 cm, bases cuneate, margins entire (undulate), faces glabrous (glaucous).
0.3–17 cm.
2–7.5 cm.
broadly hemispheric, 9–16 mm diam.
hemispheric, 9–18 mm diam.
10–15;
laminae 15–22 mm (abaxial faces not gland-dotted).
10–14;
laminae 7–9 mm.
75+;
corollas 4–6 mm, lobes reddish;
anthers dark, appendages dark (style branches yellow).
30+;
corollas 3–3.5 mm, lobes yellow;
anthers reddish brown, appendages brownish.
15–22, broadly ovate to oblong, 7–9 × 4–5 mm, (margins ciliolate) apices obtuse to acute, sometimes mucronate, abaxial faces usually glabrous.
16–19, lance-ovate, 3.5–7 × 2–2.8 mm, (margins ciliate) apices acute, abaxial faces glabrate, sparingly gland-dotted.
(1–)3–15+.
1–7.
2.8–3 mm, glabrous or distally puberulent;
pappi of 2 aristate scales 2.5–2.8 mm.
2.8–3.2 mm, glabrous;
pappi of 2 deltate, erose scales 1–1.7 mm.
4–5.5 mm, ± 3-toothed to entire.
5.5–6.5 mm, 3-toothed (apices acute, gland-dotted).
= 34.
= 34, 51.
Helianthus atrorubens
Helianthus arizonensis
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.)
Helianthus arizonensis is morphologically similar to the polyploid H. ciliaris; H. arizonensis is diploid (or triploid) and has entirely yellow disc corollas. It is known from relatively few sites.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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