12. Helianthus petiolaris Nutt. ssp. petiolaris (prairie sunflower, Kansas sunflower, plains sunflower)

Pl. 281 c, d; Map 1199

Plants annual, with taproots. Stems solitary, (25–)40–100(–150) cm long, usually relatively stout, moderately pubescent with short, stiff, ascending hairs. Leaves well developed along the stem (usually with 8–25 nodes), mostly alternate, long-petiolate. Blades of the stem leaves 4–15 cm long, 1–8 cm wide, lanceolate to triangular-ovate (mostly 2–5 times as long as wide), flat, not folded longitudinally, tapered to truncate at the base, tapered to a usually sharply pointed tip, the margins entire or finely and sometimes somewhat irregularly toothed, flat, the surfaces moderately to densely pubescent with short, straight, appressed, somewhat pustular-based hairs (somewhat roughened to the touch), sometimes also with sparse, sessile, yellow glands, more or less with 3 main veins, the lateral pair branching from the midnerve at the base of the blade. Inflorescences rarely of solitary terminal heads, more commonly appearing as open panicles. Involucre 8–14 mm long, (10–)15–25 mm in diameter, mostly shorter than or extending about to the tips of the disc corollas, the bracts in 2–4 subequal to somewhat unequal series, lanceolate to narrowly ovate, tapered to a sharply pointed, slender, loosely ascending to more commonly spreading or recurved tip, the margins with minute, stiff, ascending to more or less spreading hairs, the outer surface moderately to densely pubescent with short, stiff, loosely ascending to spreading, pustular-based hairs (the inner surface often microscopically roughened or hairy), both surfaces sometimes also with small, sessile, yellow glands. Receptacle flat or slightly convex, the chaffy bracts 5–8 mm long, narrowly oblong-triangular, usually 3-lobed above the midpoint, the lateral lobes tapered to sharply pointed, usually straw-colored, glabrous tips, the middle lobe somewhat differentiated and tapered to a sharply pointed, usually purplish-tinged, densely and conspicuously white-hairy tip, the outer surface usually glabrous below the tip. Ray florets 12–30, the corolla 1.7–2.5 cm long, glabrous or the upper surface inconspicuously hairy toward the base, both surfaces occasionally also with minute, sessile, yellow glands. Disc florets with the corolla 4.5–6.0 mm long, reddish brown to dark purple (at least the lobes and the upper portion of the tube). Pappus of 2 scales 1.5–3.0 mm long, these narrowly lanceolate-triangular, tapered to a sharply pointed, often minutely awnlike tip, more or less papery, rarely also with 1 or 2 additional oblong scales 0.2–0.5 mm long. Fruits 3.0–4.5 mm long, narrowly wedge-shaped to obovate, flattened but usually more or less 4-angled in cross-section, the surface moderately densely and usually persistently (at least along the margins) pubescent with fine, ascending hairs, finely mottled with dark brown and lighter brown patches. 2n=34. May–October.

Uncommon, mostly south of the Missouri River (Montana to New Mexico east to Wisconsin and Missouri; Canada; introduced in the western and eastern U.S.). Upland prairies, sand prairies, and tops of bluffs; also quarries, railroads, roadsides, and open, disturbed areas, often in sandy soil.

Some plants from the southwestern United States have been segregated into one or two other subspecies, based on differences in pubescence patterns and quantitative features of the heads and florets. Missouri plants are all referable to ssp. petiolaris. For a discussion of hybridization between this species and H. annuus, see the treatment of that species.