15. Helianthus strumosus L. (pale-leaved sunflower)

Pl. 283 a, b; Map 1202

Plants perennial herbs, with slender to stout, usually long-creeping, branched rhizomes (the branches sometimes with small tubers at the tip), usually occurring in dense colonies. Stems usually solitary, less commonly appearing in small clumps, 80–200 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), all or less commonly mostly opposite, mostly short-petiolate (the petioles of the larger leaves 1–2[–3] cm long). Leaf blades 4–20 cm long, 1–10 cm wide, relatively thick-textured, lanceolate to ovate (mostly 2–5 times as long as wide), flat, not folded longitudinally, rounded to broadly angled or short-tapered at the base, tapered to a sharply pointed tip, the margins finely toothed to entire, flat, the upper surface strongly roughened with moderate to dense, minute, stout, pustular-based hairs, the undersurface sparsely to densely pubescent with somewhat softer, loosely appressed to more or less spreading hairs, less commonly glabrous or nearly so and pale green to silvery (this phase more common elsewhere), also with sparse to moderate, sessile, yellow glands, with 3 main veins, the lateral pair branching from the midnerve at or just above the base of the blade, arching upward. Inflorescences of solitary terminal heads or appearing as open clusters or occasionally open panicles. Involucre 7–12 mm long, 8–20 mm in diameter, about as long as or slightly longer than the tips of the disc corollas, the bracts in 3 or 4 subequal, overlapping series, lanceolate, tapered to a sharply pointed, loosely ascending to spreading or recurved tip, the margins with an irregular 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, sometimes also with minute, sessile, yellow glands. Receptacle convex to short-conical, the chaffy bracts 5.0–6.5 mm long, narrowly oblong to narrowly oblong-oblanceolate, often with 3 short-tapered, sharply pointed lobes at the tip, these green or straw-colored, the outer surface minutely hairy, especially toward the tip. Ray florets 8–15, the corolla 1.5–3.0(–4.0) cm long, the outer surface usually with sparse, minute hairs and scattered, minute, sessile, yellow glands. Disc florets with the corolla 5.5–6.5 mm long, the corollas yellow, the lobes often minutely hairy on the outer surface. Pappus of 2 scales 1.5–2.5 mm long, these lanceolate to narrowly triangular, tapered to a sharply pointed, often minutely awnlike tip. Fruits 4.0–5.5 mm long, wedge-shaped to 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=68, 102. July–September.

Scattered nearly throughout the state (eastern U.S. west to Wisconsin, Kansas, and Texas; Canada). Bottomland forests, mesic upland forests, banks of streams and rivers, bases and ledges of bluffs, fens, and upland prairies; also railroads and roadsides.

Although apparently reasonably distinct elsewhere in its range, this species can be very difficult to distinguish from H. hirsutus in Missouri, especially in the Ozarks. Plants with slightly hairy, nonglaucous stems and the leaf undersurface relatively hairy are encountered with some frequency. How much of this variation represents the results of introgressive hybridization between the taxa is not known and requires further detailed genetic study. Heiser et al. (1969) thought that these plants, which they considered a tetraploid (2n=64) race, might as easily be accommodated in H. hirsutus. It is possible that future studies may show that the apparent separation of H. strumosus from H. hirsutus is an illusion and that these should be combined as a single species, perhaps with two or more varieties to account for the various races.

Occasional specimens also can be difficult to distinguish from H. divaricatus and H. tuberosus. Heiser et al. (1969) discussed a hexaploid (2n=102) race of H. strumosus from Illinois, Missouri, Arkansas, and Oklahoma, which had been named H. formosus S. Watson. These plants were characterized as having the leaf undersurface strongly glaucous and the rhizomes with well-defined, small tubers.