Helianthus debilis
Helianthus schweinitzii
cucumberleaf sunflower, weak sunflower
Schweinitz's sunflower
decumbent to erect, glabrous, hirsute, or puberulent.
(often reddish, leafy) erect, ± strigose proximally, strigose or glabrous distally.
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 (proximal) or alternate;
petioles 0–1 cm;
blades (light to dark green, 3-nerved distal to bases) lanceolate to lance-linear, 6–18 × 1–2 cm, bases cuneate, margins entire or subentire (revolute), faces hirsute to tomentose and gland-dotted (abaxial) or scabrous (adaxial).
9–50 cm.
1.5–8 cm (not gland-dotted).
hemispheric, 10–22 mm diam.
hemispheric, 9–10(–16) mm diam.
11–20;
laminae 12–23 mm.
8–15;
laminae 15–22 mm (abaxial faces gland-dotted).
30+;
corollas 4.5–5 mm, lobes usually reddish, sometimes yellow;
anthers dark, appendages dark (style branches usually reddish, rarely yellow).
40+;
corollas 5–6 mm, lobes yellow;
anthers dark brown to black, appendages dark or reddish brown.
20–30, lanceolate, 8–17 × 1–3 mm, apices acute to long-attenuate, abaxial faces glabrous or ± hispid, not gland-dotted.
16–20 (reflexed or loose), lanceolate or lance-ovate, 5–7 × 1.5–2.3 mm, apices acute to acuminate, abaxial faces hirsute (proximally) to glabrate, gland-dotted.
1–3.
3–6.
2.5–3.2 mm, glabrous or sparsely hairy;
pappi of 2 lanceolate or lance-linear scales 1.2–2.5 mm.
3–4 mm, glabrate;
pappi of 2 aristate scales 1.5–2 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 hairy).
= 68.
Helianthus debilis
Helianthus schweinitzii
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.)
Of conservation concern.
Helianthus schweinitzii is distinguished by its relatively small heads and sessile to subsessile, narrowly lanceolate leaves with revolute margins. Chromosome number, typification issues, and identification of voucher specimens were updated by J. F. Matthews et al. (1997).
Helianthus schweinitzii is found on the Carolina piedmont. It was listed as endangered in the Federal Register on May 7, 1991, and is known from 16 populations. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(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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