9.
Helianthus petiolaris
Nuttall, J. Acad. Nat. Sci. Philadelphia. 2: 115. 1821.
Prairie sunflower
Annuals,
40—200 cm.
Stems
erect, usually densely canescent, hispid, or strigillose, rarely ± hirsute or glabrate.
Leaves
mostly cauline; mostly alternate; petioles 2—4 cm; blades (often bluish green) lanceolate to deltate-ovate or ovate, 4—15 × 1—8 cm, bases subcordate or truncate to cuneate, margins entire or ± serrate, abaxial faces strigose, sparsely to densely, or not at all, gland-dotted.
Heads
1—5.
Peduncles
4—15(—40) cm.
Involucres
± hemispheric, 10—24 mm diam.
Phyllaries
14—25, lance-linear to lanceolate to lance-ovate, 10—14 × 1—4(—5) mm, (margins sometimes ciliate) apices short-attenuate, abaxial faces usually hispidulous, rarely sparsely hirsute to glabrate.
Paleae
4.5—7.5 mm, 3-toothed, middle teeth ± ciliate or bearded, hairs whitish, 0.5—0.7 mm.
Ray florets
10—30; laminae 15—20 mm.
Disc florets
50—100+; corollas 4.5—6 mm, lobes usually reddish, rarely yellow; anthers reddish to purplish, appendages purplish (style branches reddish).
Cypselae
3—4.5 mm, ± villous;
pappi
of 2 aristate scales 1.5—3 mm plus 0—2 erose scales 0.3—0.5 mm.
2
n
= 34.
Subspecies 2 (2 in the flora): w North America.
Helianthus petiolaris
is adventive beyond western North America.
A third subspecies has yet to be named at that rank in
Helianthus petiolaris
; it has been called
H. petiolaris
var.
canescens
A. Gray. It differs in having stems, leaves, and phyllaries densely canescent and abaxial faces of leaves densely gland-dotted. It is additionally characterized by peduncles usually ebracteate, phyllaries 1—2 mm wide, disc corolla throats gradually narrowed distal to slight, not densely hairy basal bulges, and
2
n
= 34. It flowers late spring through late summer and grows on sandy soils in open areas at (10—)1000—2300 m in Arizona, California, Nevada, New Mexico, and Texas and in Mexico. It was treated as
H. niveus
(Bentham) Brandegee subsp.
canescens
(A. Gray) Heiser by C. B. Heiser et al. (1969); molecular and morphologic data appear to favor a placement within
H. petiolaris
.
