Helianthus debilis
Helianthus arizonensis
cucumberleaf sunflower, weak sunflower
Arizona sunflower
decumbent to erect, glabrous, hirsute, or puberulent.
erect to ascending, glabrous (glaucous).
mostly cauline; mostly alternate;
petioles 1–7 cm;
blades deltate-ovate, lance-ovate, or ovate, 2.5–14 × 1.8–13 cm, bases cordate to truncate or broadly cuneate, margins subentire to serrate, abaxial faces glabrate to hispid, not gland-dotted.
cauline; opposite;
sessile;
blades (bluish green) lanceolate, 2–7 × 0.5–1.3 cm, bases cuneate, margins entire (undulate), faces glabrous (glaucous).
9–50 cm.
2–7.5 cm.
hemispheric, 10–22 mm diam.
hemispheric, 9–18 mm diam.
11–20;
laminae 12–23 mm.
10–14;
laminae 7–9 mm.
30+;
corollas 4.5–5 mm, lobes usually reddish, sometimes yellow;
anthers dark, appendages dark (style branches usually reddish, rarely yellow).
30+;
corollas 3–3.5 mm, lobes yellow;
anthers reddish brown, appendages brownish.
20–30, lanceolate, 8–17 × 1–3 mm, apices acute to long-attenuate, abaxial faces glabrous or ± hispid, not gland-dotted.
16–19, lance-ovate, 3.5–7 × 2–2.8 mm, (margins ciliate) apices acute, abaxial faces glabrate, sparingly gland-dotted.
1–3.
1–7.
2.5–3.2 mm, glabrous or sparsely hairy;
pappi of 2 lanceolate or lance-linear scales 1.2–2.5 mm.
2.8–3.2 mm, glabrous;
pappi of 2 deltate, erose scales 1–1.7 mm.
7.5–8 mm, apices 3-toothed (middle teeth acuminate, usually glabrous or hispid, sometimes ± villous or bearded).
5.5–6.5 mm, 3-toothed (apices acute, gland-dotted).
= 34, 51.
Helianthus debilis
Helianthus arizonensis
Subspecies 5 (5 in the flora).
C. B. Heiser (1956) placed 8 subspecies in Helianthus debilis; he noted that alternative taxonomic treatments might recognize these in as many as three species, or expand the single species to include H. petiolaris. Later, Heiser et al. (1969) separated three of the subspecies as H. praecox. Isozyme data (R. P. Wain 1982, 1983; L. H. Rieseberg and M. F. Doyle 1989) show that all are closely related. Documented hybridization with H. annuus further complicates the situation. The treatment by Heiser et al. is followed here.
Helianthus debilis is adventive beyond the Atlantic and Gulf coasts of the United States.
(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.)
1. Stems decumbent; peduncles 9–20(–22) cm | → 2 |
1. Stems erect; peduncles (15–)20–50 cm | → 3 |
2. Stems glabrous or puberulent; leaf blades serrulate or shallowly, regularly serrate, abaxial faces sparsely, if at all, gland-dotted | subsp. debilis |
2. Stems hirsute; leaf blades deeply, irregularly serrate, abaxial faces densely gland-dotted | subsp. vestitus |
3. Leaves 8–14 cm; peduncles (relatively slender) 20–40 cm; discs 10–15(–17) mm diam | subsp. silvestris |
3. Leaves 2.5–9 cm; peduncles (not notably slender) 10–50 cm; discs 14–20 mm diam | → 4 |
4. Leaf blades usually deeply, irregularly serrate; peduncles 10–25(–30) cm; ray lami-nae 12–20(–22) mm | subsp. tardiflorus |
4. Leaf blades usually shallowly, regularly serrate; peduncles 25–50 cm; ray laminae (15–)20–23 mm | subsp. cucumerifolius |
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