3. Helianthus decapetalus L. (thin-leaved sunflower, pale sunflower)

Pl. 282 e, f; Map 1190

Plants perennial herbs, with relatively slender, long-creeping, branched rhizomes (some of the branches rarely with small tubers at the tip), usually occurring in dense colonies. Stems usually appearing loosely clumped, less commonly solitary, 60–200 cm long, glabrous below the inflorescence or the uppermost portion of the stem sparsely pubescent with short, stiff, loosely ascending, pustular-based hairs, often somewhat glaucous. Leaves well developed along the stem (usually with 8–20 nodes), mostly opposite (often alternate in the upper third), short- to long-petiolate (the petioles of the larger leaves usually 2–5 cm long and somewhat winged toward the tip). Leaf blades 6–20 cm long, (1.5–)3.0–10.0 cm wide, relatively thin-textured, lanceolate to ovate (mostly 2–5 times as long as wide), flat, not folded longitudinally, rounded to tapered at the base, tapered to a sharply pointed tip, the margins finely to more commonly (at least on larger leaves) coarsely toothed, flat, the upper surface strongly roughened with moderate, minute, stout, pustular-based hairs, the undersurface glabrous (and usually pale green to silvery) or sparsely to moderately pubescent with stiff or somewhat softer, loosely appressed hairs and with sparse, sessile, yellow glands, more or less with 3 main veins, the lateral pair sometimes relatively thin, branching from the midnerve at or near the base of the blade, arching upward. Inflorescences of solitary terminal heads or appearing as open clusters or occasionally open panicles. Involucre 12–18 mm long, 12–25 mm in diameter, conspicuously longer than the tips of the disc corollas, the bracts in 3 or 4 subequal, overlapping series, narrowly lanceolate, tapered to a sharply pointed, spreading or recurved tip, the margins with a fringe of short, spreading to ascending hairs, the outer surface glabrous or more commonly sparsely to moderately pubescent with short, stout, ascending, often pustular-based hairs, usually lacking glands. Receptacle convex to short-conical, the chaffy bracts 8–10 mm long, narrowly oblong to narrowly oblong-oblanceolate, with 3 short-tapered, sharply pointed lobes at the tip, these straw-colored, the outer surface minutely hairy toward the tip. Ray florets 8–15, the corolla 1.5–3.5 cm long, yellow to pale yellow, the outer surface usually with sparse, minute hairs. Disc florets with the corolla 6.5–7.5 mm long, the corollas yellow, the lobes often minutely hairy on the outer surface. Pappus of 2 scales 3–4 mm long, these lanceolate to narrowly triangular, tapered to a sharply pointed, often minutely awnlike tip. Fruits 3.5–5.0 mm long, wedge-shaped to narrowly obovate, somewhat flattened and more or less bluntly 4-angled in cross-section, the surface glabrous or with a few minute hairs at the tip, uniformly brown or with fine, darker and lighter brown mottling. 2n=34, 68. July–October.

Uncommon in the northeastern portion of the state (eastern [mostly northeastern] U.S. west to Wisconsin, Iowa, and Missouri). Banks of streams and rivers, bottomland forests, mesic upland forests in ravines, and bases and ledges of bluffs.

Steyermark’s (1963) treatment of H. decapetalus differed sharply from that of Heiser et al. (1969). He accepted the species as occurring in eleven counties, mostly in a diagonal band from the northeastern to southwestern corners of the state, but also in the Bootheel and in Jackson County. All but one of these specimens subsequently were annotated by Heiser and his colleagues as either H. divaricatus or H. strumosus, and they did not include Missouri in their distribution map of the species. In its typical phase, the thin leaves with well-developed petioles and relatively coarse, blunt teeth are good morphological markers for H. decapetalus. The confusion among the taxa involved may be blamed in part on the presence of tetraploid populations, which apparently are inherently more variable morphologically than are the diploids. As noted by Steyermark (1963), further studies are still needed to accurately assess the status and range of H. decapetalus in Missouri.