Oneflower Helianthella

Two infraspecific taxa within Helianthella uniflora may be distinguished; they have been named at varietal rank.

Variety douglasii has stems hirsute; involucres (15–)20–25(–30) mm diam.; outer phyllaries rarely elongated, margins ciliate, abaxial faces sparsely puberulent; ray laminae 30–40 mm; and 2n = 30. It grows in grasslands in the northern Rocky Mountains and on the east side of the Cascade Range (B.C.; Idaho, Oreg., Wash.) at 300–2500 m where it flowers May–Jul.

Variety uniflora has stems sparingly puberulent to scabrous; involucres 15–20(–25) mm diam.; outer phyllaries frequently elongated, margins not ciliate, abaxial faces uniformly cinereous-pubescent; ray laminae 20–30 mm; and 2n = 30. It grows in meadows, sagebrush scrublands, swales, aspen forests, rocky slopes, and spruce-fir forests of the Rocky Mountains, intermountain plateaus, and Great Basin ranges (Ariz., Colo., Idaho, Mont., Nev., Oreg., Utah, Wyo.) at 1500–3400 m, where it flowers (May–)Jun–Jul(–Aug).

Plants 40–120 cm. Cauline leaves: largest at mid stems; blades usually 3-nerved, usually lanceolate to elliptic, rarely ovate, 12–25 cm, faces puberulent, hirsute, or scabrous. Heads usually borne singly, sometimes 2–3+, erect. Involucres turbinate to hemispheric or broader, 15–30 mm diam. Phyllaries lanceolate to lance-linear (subequal or outer larger, margins sometimes ciliate, faces ± cinereous-pubescent to sparsely puberulent). Paleae chartaceous, relatively firm. Ray florets 11–13(–21); laminae 15–30(–45) mm. Disc corollas yellow. Cypselae strongly compressed, narrowly obovate (margins ciliate, faces strigose); pappi of 2 ± subulate scales plus 2–4 shorter scales. 2n = 30.

Helianthus uniflorus Nuttall, J. Acad. Nat. Sci. Philadelphia 7: 37. 1834; Helianthella uniflora var. douglasii (Torrey & A. Gray) W. A. Weber

Helianthella uniflora, the oneflower helianthella, is a North American plant species in the family Asteraceae. It grows in the western United States and western Canada. It has been found from British Columbia south as far as northern Arizona and northern New Mexico.

Helianthella uniflora is a herbaceous plant up to 120 cm (3.9 ft) tall. Leaves are up to 25 cm (9.8 in) long, each with 3 prominent veins running the length of the leaf. The plant usually produces only one yellow flower head per stem, though sometimes 2 or 3, the heads not nodding (hanging). Each head contains 11-21 bright yellow ray flowers surrounding numerous yellow disc flowers.