| | 1. Petals white or rose to ± purple; seeds in 1 row per chamber or clustered (fruit not tubercled) or in 2 rows per chamber (fruit tubercled) |
| |
| | 2. Fruit much wider toward tip; petals white, rose, or rose-purple; seeds clustered |
| |
| | 3. Hypanthium 4–8 mm; petals 5–10 mm; fruit base tapered (sect. Hartmannia) |
| O. rosea |
| | 3' Hypanthium 10–23 mm; petals 25–40 mm; fruit base cylindric (sect. Xylopleurum) |
| O. speciosa |
| | 2' Fruit narrower toward tip (except slightly wider in O. stricta); petals white; seeds in rows |
| |
| | 4. Stem not peeling; bud erect; fruit 4–9 mm wide, tubercled; seeds in 2 rows per chamber, with an obvious cavity on 1 side (sect. Pachylophus) |
| O. caespitosa |
| | 5. Fruit 10–34 mm, lanceolate to elliptic-ovate, generally S-shaped, stalk-like base 0–1 mm; petals fading rose to purple; margin of seed-cavity lobed |
| subsp. crinita |
| | 5' Fruit 25–68 mm, cylindric, ± straight, stalk-like base 0–55 mm; petals fading lavender to pink; margin of seed-cavity entire |
| subsp. marginata |
| | 4' Stem peeling; bud nodding; fruit 1.5–5 mm wide, not tubercled; seeds in 1 row per chamber, cavity 0 (sect. Anogra) |
| |
| | 6. Perennial; new shoots generally from lateral roots; free sepal tips in bud 0 or < 1 mm |
| O. californica |
| | 7. Stem hairs dense, short, appressed and long, spreading, wavy; roots fleshy; new rosettes at stem tips |
| subsp. eurekensis |
| | 7' Stem hairs 0 (to dense, short, appressed and long, spreading); roots not fleshy; new rosettes not forming at stem tips |
| |
| | 8. Cauline leaves generally ± pinnately lobed; plant ± grayish green; |
| subsp. avita |
| | 8' Cauline leaves subentire to deeply wavy-dentate; plant green to slightly grayish |
| subsp. californica |
| | 6' Annual or perennial herb; new shoots from lateral roots 0; free sepal tips in bud 0–1 mm (plant annual or short-lived perennial herb) or 1–9 mm (plant per) |
| O. deltoides |
| | 9. Grayish green per; free sepal tips in bud 1–9 mm |
| subsp. howellii |
| | 9' Green annual or short-lived perennial herb; free sepal tips in bud 0–1 mm |
| |
| | 10. Upper leaves pinnately lobed; stem generally < 1 dm; petals 15–25(30) mm |
| subsp. piperi |
| | 10' Upper leaves subentire to ± dentate, rarely pinnately lobed; stem generally 2–10 dm; petals 15–40 mm |
| |
| | 11. Spreading hairs ± 2 mm above; fruit base 3–5 mm wide |
| subsp. cognata |
| | 11' Spreading hairs 1–1.5 mm above; fruit base 2–3 mm wide |
| subsp. deltoides |
| | 1' Petals yellow; seeds generally in 2 rows per chamber (fruit not tubercled, but hairs sometimes with red blister-like bases) |
| |
| | 12. Stem erect; biennial; flowers in generally dense spikes; seeds angled, irregularly pitted (sect. O. subsect. Oenothera) |
| |
| O. longissima |
| |
| | 14. Petals 25–52 mm; stigma well above anthers; pollen ± all fertile or ± 50% sterile (sterile grains small and shriveled at 10×) |
| |
| | 15. Leaf crinkled; seeds and pollen ± 50% sterile |
| O. glazioviana |
| | 15' Leaf ± flat, ± not crinkled; seeds and pollen ± all fertile |
| O. elata |
| | 16. Sepals green or red-flushed; red blister-like hair bases ± 0; anthers 8–15 mm |
| subsp. hirsutissima |
| | 16' Sepals red-flushed; red blister-like hair bases obvious; anthers 12–23 mm |
| subsp. hookeri |
| | 14' Petals 7–25(30) mm; stigma ± not above anthers; pollen ± 50% sterile |
| |
| | 17. Petals 13–23 mm, generally < sepals; coastal |
| O. wolfii |
| | 17' Petals 7–25(30) mm, ± = sepals; generally not near coast |
| |
| | 18. Spike dense (internodes in fruit < fruit); longest hairs generally without red blister-like bases; petals 10–25(30) mm; sepals generally green or yellowish (reddish) |
| O. biennis |
| | 18' Spike ± open (internodes in fruit generally > fruit); longest hairs generally with red blister-like bases; petals 7–20 mm; sepals often marked reddish |
| O. villosa subsp. strigosa |
| | 12' Stem ± 0, decumbent, or erect; annual or perennial herb (except O. stricta biennial); flowers few, in upper axils; seeds not both angled and irregularly pitted |
| |
| | 19. Fruit winged; seeds obliquely wedge-shaped (sect. Lauvaxia) |
| O. flava subsp. flava |
| | 19' Fruit not winged (sharply angled in O. xylocarpa); seeds ± round to oblanceolate |
| |
| | 20. Fruit lanceolate to ovate, 4–11 mm wide; seed 2.4–3.5 mm, ± wrinkled; pollen ± all fertile |
| |
| | 21. Petals fading deep salmon-red; fruit generally ± twisted; 1 side of seed with 2 small ridges; c&s High Sierra Nevada (sect. Contortae) |
| O. xylocarpa |
| | 21' Petals fading reddish purple to orange; fruit not twisted; 1 side of seed with thick, U-shaped area surrounding a groove; Desert (sect. Eremia) |
| O. primiveris |
| | 22. Leaf grayish green; petals (22)29–40 mm; stigma above anthers |
| subsp. bufonis |
| | 22' Leaf generally green; petals 6–25(28) mm; stigma ± not above anthers |
| subsp. primiveris |
| | 20' Fruit cylindric (sometimes slightly wider toward tip), 2–4 mm wide; seed 1–1.8 mm, pitted; pollen ± 50% sterile |
| |
| | 23. Bud erect; petal base generally with a red spot; fruit slightly wider toward tip (sect. O. subsect. Munzia) |
| O. stricta subsp. stricta |
| | 23' Bud nodding or curved upward; petal base unspotted; fruit tapered to tip |
| |
| | 24. Bud curved upward; sepal free tips in bud 0.3–3 mm (sect. O. subsect. Raimannia) |
| O. laciniata |
| | 24' Bud nodding; sepal free tips in bud 0.1–1 mm (sect. O. subsect. Nutantigemma) |
| O. pubescens
|