42.
Helianthus grosseserratus
M. Martens, Index Seminum (Louvain). 1839: unpaged. 1839.
Sawtooth sunflower, hélianthe à grosses dents
Helianthus instabilis
E. Watson
Perennials
, 100—400(—500) cm (rhi-zomatous).
Stems
erect, glabrous proximally, distally glabrate, scabrellous, or strigillose (glaucous).
Leaves
cauline; opposite (proximal) or alternate; petioles (1—)2—5 cm; blades (light to dark green, 3-nerved distal to bases) lanceolate to lance-ovate, 10—32 × (1.2—)4—9 cm, bases cuneate, margins usually coarsely to shallowly serrate, rarely subentire (flat), abaxial faces puberulent to tomentulose, gland-dotted.
Heads
3—15+.
Peduncles
0.3—10 cm.
Invo-lucres
broadly hemispheric, 15—25 mm diam.
Phyllaries
25—30 (loose, spreading
),
lance-linear, 10—14 × 1.5—2.5 mm (subequal), (margins ± ciliate) apices attenuate, abaxial faces glabrous or puberulent, not gland-dotted.
Paleae
7—8 mm, entire or 3-toothed (apices acuminate, ± hairy).
Ray florets
14—20; laminae 23—40 mm.
Disc florets
100+; corollas 5—6 mm, lobes yellow; anthers dark brown to black, appendages yellow.
Cypselae
3—4 mm, glabrate;
pappi
of 2 aristate scales 1.9—2.5 mm.
2
n
= 34.
Flowering late summer—fall. Dry to wet prairies, other open sites; 10—300+ m; Ont., Que.; Ark., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., S.Dak., Tenn., Tex., Va., Wash., W.Va., Wis.
Helianthus grosseserratus
is native to midwestern North America and has spread as a roadside weed into other areas, such as New England and the southeastern United States. It is introduced in Canada. Hybrids between
H. maximiliani
and
H. grosseserratus
are known as
H.
×
intermedius
R. W. Long (R. W. Long 1954; Long 1966). Hybrids of
H. grosseserratus
with
H. salicifolius
have been described as
H
.
kellermannii
Britton (Long 1955), and those with
H. mollis
as
H
.
brevifolius
E. Watson (R. C. Jackson and A. T. Guard 1957b).
