Herbs perennial, short-lived or suffrutescent, or annual. Leaves: blade margins subentire or serrulate or spinulose-serrate. Flowers usually crowded near stem apex; buds quadrangular; floral-tube 2–20 mm; sepals with keeled midrib; stamens in 2 unequal series, antisepalous set conspicuously longer, pollen 30–100% fertile. Capsules hard, straight or, sometimes, slightly recurved, tardily dehiscent 1/2 to throughout their length. Seeds obovoid or oblanceoloid, sometimes sharply angled. 2n = 14.

Distribution

w, c North America, n Mexico

Discussion

Species 3 (3 in the flora).

Subsection Calylophus consists of three species (four taxa), one of which (Oenothera capillifolia) occurs primarily in Texas, but extends to southeastern Colorado, southern Kansas, southern Louisiana, and northeastern Mexico, and is disjunct in northwestern New Mexico; O. serrulata occurs throughout the Great Plains to Alberta, Manitoba, and Saskatchewan east to Wisconsin, west to east-central Arizona, with one occurrence in Chihuahua, Mexico, at elevations 0–1800(–2100) m. Species of subsect. Calylophus have diurnal flowers.

Selected References

None.

Lower Taxa

Oenothera capillifolia, Oenothera gayleana, Oenothera serrulata

Key

1	Petals 5–12(–20) mm; stigmas surrounded by anthers at anthesis; pollen 30–60(–80)% fertile.	Oenothera serrulata
1	Petals 6–25 mm; stigmas exserted beyond anthers at anthesis; pollen 90–100% fertile.	> 2
2	Leaves (0.1–)0.3–1 cm wide; stems (10–)25–80 cm, 1–many, unbranched to moderately branched, weakly decumbent to erect; sepals 4–12 mm; floral tube 5–20 mm; petals 6–25 mm.	Oenothera capillifolia
2	Leaves 0.1–0.2 cm wide; stems 15–30(–40) cm, many, branched from base, ascending to erect; sepals 4–6 mm; floral tube 7 mm; petals 15–20 mm.	Oenothera gayleana

"/2" is not declared as a valid unit of measurement for this property."thin" is not a number.