Oenothera tanacetifolia Torrey & A. Gray in War Department [U.S.], Pacif. Railr. Rep. 2(1): 121, plate 4. 1857; Camissonia tanacetifolia (Torrey & A. Gray) P. H. Raven; C. tanacetifolia subsp. quadriperforata P. H. Raven; Taraxia longiflora Nuttall ex Raimann; T. tikurana A. Nelson

Herbs usually densely, sometimes sparsely, short-hirtellous, hairs spreading or appressed, and/or sparsely to densely strigillose; taproot deep, woody, with numer­ous slender branches in age, producing new rosettes. Leaves 6.5–32 × 0.7–3.3 cm; petiole not winged, 1–8 cm; blade very narrowly elliptic, base attenuate to narrowly cuneate, margins deeply and irregularly pinnatifid, apex acute to long-acuminate. Flowers opening near sunrise; floral tube 4–6.5(–8.5) mm, soft-pilose in proximal 1/2 inside; sepals 5.5–13 mm; petals yellow, (8–)10–23 mm; episepalous staminal filaments 5.5–12 mm, epipetalous ones 2.5–8 mm, anthers (2.3–)2.8–3.5 mm; sterile prolongation of ovary 14–55 mm, style 9.5–20(–25) mm, pilose near base, stigma exserted beyond anthers at anthesis. Capsules subterete, cylindric-ovoid, 7–25 × 3–5 mm, walls thick, evidently distended by seeds; sessile. Seeds uniformly tan to brown, curved-cylindric, 1.5–2 × 0.6–0.8 mm, pitted in rows. 2n = 14, 28, 42.

Flowering May–Jul. Open areas on clay soil, moist swales and meadows, dry streambeds, edges of drying ponds; 400–2500 m; Calif., Idaho, Nev., Oreg., Wash.

P. H. Raven (1969) determined that the majority of plants examined cytologically were tetraploid (2n = 28), making one diploid (2n = 14) determination. Raven also found hexaploid plants in a restricted area from Sierra Valley in Plumas and immediately adjacent Lassen and Sierra counties, California. They do not differ morphologically from diploid and tetraploid plants other than having greater than ten percent of pollen grains 4-pored, but there was no known diploid population that could have combined with tetraploids to give rise to this hexaploid. Raven named it Camissonia tanacetifolia subsp. quadriperforata; however, it is not currently recognized due to the lack of morphological differentiation. Raven also found Taraxia tanacetifolia to be primarily self-incompatible with possibly some self-compatible plants occurring.

Oenothera nuttallii Torrey & A. Gray 1840 (not Sweet 1830) pertains here.