14. Helianthus silphioides Nutt. (rosinweed sunflower)

Pl. 283 c, d; Map 1201

Plants perennial herbs, lacking rhizomes or with very short, thick rhizomes, often occurring as clumps. Stems solitary or more commonly few to several, 80–250(–300) cm long, sparsely to densely pubescent with short, ascending, slender hairs and/or more or less spreading, short, stiff, pustular-based hairs toward the base, usually glabrous above the midpoint. Leaves well developed along the stem (usually with 8–15 nodes), all or mostly opposite, mostly with an unwinged, short petiole 1–4 cm long. Blades of the stem leaves 3–15 cm long, 1–15 cm wide, ovate to broadly ovate or nearly circular (mostly 1.0–1.7[–2.0] times as long as wide), the uppermost leaves occasionally somewhat narrower, flat, not folded longitudinally, rounded or abruptly short-tapered at the base, rounded or broadly angled to a bluntly pointed tip, the margins finely toothed or scalloped to nearly entire, flat, the surfaces strongly roughened with moderate, minute, stout, pustular-based hairs, but lacking 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 open clusters or open panicles. Involucre 8–15 mm long, 10–20 mm in diameter, slightly shorter than to about as long as the tips of the disc corollas, the bracts in 3 or 4 noticeably unequal, overlapping series, oblong to oblong-ovate, rounded or narrowed to a bluntly pointed, tightly appressed tip, the margins often with a fringe of minute, spreading hairs, the outer surface glabrous or sparsely hairy toward the base but lacking glands. Receptacle convex, the chaffy bracts 8–10 mm long, narrowly oblong to narrowly oblong-oblanceolate, angled or short-tapered to a sharply pointed, green, straw-colored, or purplish-tinged, glabrous tip, occasionally with a pair of additional short, broad lobes toward the tip, the outer surface also usually glabrous. Ray florets (8–)12–15, the corolla 1.5–2.0 cm long, glabrous or the outer surface with inconspicuous, short, slender hairs along the veins. Disc florets with the corolla 6–7 mm long, the corollas reddish brown to dark purple (at least the lobes and the upper portion of the tube), the lobes and tip of the tube often minutely hairy on the outer surface. Pappus of 2 scales 2.5–3.0 mm long, these lanceolate to narrowly triangular, sometimes with an irregular pair of small basal lobes, tapered to a sharply pointed, often minutely awnlike tip. Fruits 3.0–4.5 mm long, narrowly wedge-shaped to narrowly obovate, flattened but sometimes more or less 4-angled in cross-section, the tip and margins moderately to densely pubescent with short, ascending hairs, the surface otherwise glabrous, uniformly dark brown or more commonly with fine, darker and lighter brown mottling. 2n=34. August–October.

Scattered in the Mississippi Lowlands Division and westward along the southern portion of the Ozarks to McDonald County (Oklahoma, Missouri, Illinois, and Kentucky south to Arkansas, Tennessee, Louisiana, Mississippi, and Alabama). Banks of streams, sand prairies, and openings of mesic to dry upland forests; also fallow fields, fencerows, and roadsides.

Steyermark (1963) noted that this showy species does well in the wildflower garden.