37.
Helianthus angustifolius
Linnaeus, Sp. Pl. 2: 906. 1753.
Swamp sunflower
Helianthus angustifolius
var.
planifolius
Fernald
Perennials
, 50—150+ cm (with crown buds, rhizomes absent or poorly developed).
Stems
erect, usually ± hairy.
Leaves
mostly cauline; opposite or alternate; sessile or subsessile; blades (3-nerved near bases) narrowly lanceolate to linear, 8—15 × 0.15—0.5(—1) cm, bases cuneate , margins entire (revolute, abaxial face sometimes obscured by rolled margins), abaxial faces strigose to hispid or hirsute, sometimes (adaxial not) gland-dotted.
Heads
3—16.
Peduncles
5—15 cm.
Involucres
shallowly hemispheric, 10—20 mm diam.
Phyllaries
25—32 (loose), lanceolate, 4—9 × 1—2 mm, apices acute to slightly acuminate, abaxial faces usually scabrous, rarely glabrous, usually gland-dotted.
Paleae
(oblanceolate) 5.5—6.5 mm, entire or ± 3-toothed (apices purplish, mucronate, gland-dotted).
Ray florets
10—20; laminae 10—20 mm (abaxial faces gland-dotted).
Disc florets
75+; corollas 4—4.5 mm, lobes yellow; anthers dark brown or black, appendages dark (style branches usually yellow).
Cypselae
2—3 mm, glabrate;
pappi
of 2 aristate scales 1.5—2.1 mm.
2
n
= 34.
Flowering late summer—fall. Open to shaded, usually moist places; 10—700 m; Ala., Ark., Fla., Ga., Ind., Iowa, Ky., La., Md., Miss., Mo., N.J., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va.
The distal parts of
Helianthus angustifolius
are identical in appearance to those of
H. simulans
; plants of the latter are taller (200+ cm) and more robust. The leaves are not only narrower in
H. angustifolius
but also tend to be more strongly revolute (abaxial faces sometimes scarcely visible).
