Rosinweed Sunflower

Similar to Helianthus atrorubens, H. silphioides is distinguished by shorter hairs (less than 2 mm ) on stems proximally and on abaxial leaf midveins, and by petioles of basal leaves less than ¹/2 lengths of blades and winged less than ¹/2 their lengths. As befits the name, specimens of H. silphioides (and also H. atrorubens) are not infrequently misidentified as species of Silphium.

Perennials, 50–300 cm (with crown buds; nonflowering stems usually present). Stems erect, hispid to strigoso-hispid proximally, glabrate distally. Leaves basal and cauline; mostly opposite; petioles 0.1–5.5 cm; blades ovate to broadly ovate or suborbiculate, 7–15 × 4.5–15 cm, bases rounded to truncate or ± cuneate, margins entire or crenate to serrate, abaxial faces usually scabrous, sometimes ± strigose (hairs on midribs to 1 mm), not gland-dotted (cauline 9+ pairs proximal to heads, smaller ). Heads 3–15+. Peduncles 0.5–10 cm. Involucres hemispheric, 10–20 mm diam. Phyllaries 16–23, oblong to obovate, 8–10 × 3–5 mm, (margins ciliolate) apices obtuse to acute, sometimes mucronate, abaxial faces glabrous or glabrate. Paleae 9–10 mm, entire or ± 3-toothed. Ray florets 8–13; laminae 15–20 mm (abaxial faces not gland-dotted). Disc florets 75+; corollas 6–7 mm, lobes reddish; anthers dark, appendages dark (style branches yellow ). Cypselae 3–4 mm, glabrous or distally puberulent; pappi of 2 aristate scales 2.5–2.7 mm. 2n = 34.

Helianthus kentuckiensis F. T. McFarland & W. A. Anderson

Helianthus silphioides is a North American species of sunflower known by the common names rosinweed sunflower or Ozark sunflower. It is native to the central United States, primarily in the Ozarks and the Tennessee Valley with additional populations north into Kentucky and Illinois and south as far as Louisiana, Mississippi and Alabama.

Helianthus silphioides grows in open locations. It is an perennial herb up to 300 cm (10 feet) tall. Leaves are broadly egg-shaped. One plant usually produces 3-15 flower heads, each containing 8–13 yellow ray florets surrounding 75 or more red disc florets.

A 2004 Illinois conservation assessment listed Helianthus silphioides as critically imperiled within the state. The species is also considered endangered within Kentucky, likely due to habitat loss of open oak woodlands and barrens. Throughout the remained of its range, it is considered apparently secure or conservation status is unknown.