41.
Helianthus giganteus
Linnaeus, Sp. Pl. 2: 905. 1753.
Giant or tall sunflower, hélianthe géant
Helianthus alienus
E. Watson;
H. validus
E. Watson
Perennials
, 100—400 cm (rhi-zomatous).
Stems
(usually reddish) erect, hairy.
Leaves
cauline; mostly alternate; petioles 0—1.2 cm (ciliate); blades (3-nerved from bases) lanceolate to lance-ovate, 7—20 × 1.2—3.5 cm, bases cuneate, margins serrulate to subentire (± flat), abaxial faces scabrous or ± hirsute, sometimes gland-dotted.
Heads
1—12.
Peduncles
8—12 mm.
Involucres
hemispheric, 10—24 mm diam.
Phyllaries
20—25 (loose or spreading), linear, 8—15 × 1.2—2 mm, (margins usually ciliate) apices acute to attenuate , abaxial faces sparsely strigose, not gland-dotted.
Paleae
7—9 mm, entire or ± 3-toothed (apices acute, hairy).
Ray florets
12—20; laminae (often pale yellow) 15—25 mm (abaxial faces not gland-dotted).
Disc florets
60+; corollas 5—6 mm, lobes yellow; anthers dark brown or black, appendages dark.
Cypselae
3—4 mm, glabrate;
pappi
of 2 aristate scales 2.4—3 mm.
2
n
= 34.
Flowering late summer—fall. Usually wet, open sites; 10—600+ m; N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que.; Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Miss., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Vt., Va., W.Va., Wis.
Helianthus giganteus
was probably introduced in Newfoundland. It intergrades with
H. nuttallii
and
H. grosseserratus
; it is distinctive in its hairy, reddish-colored stems, dark anther appendages, and prominent setae on the petioles. The natural hybrid of
H. giganteus
with
H. grosseserratus
has been called
H.
luxurians
E. Watson (R. W. Long 1954). Hybrids of
H. giganteus
with
H. divaricatus
have been referred to as
H
.
ambiguus
(Torrey & A. Gray) Britton and
H
. ×
divariserratus
R. W. Long (Long 1954).
