Oenothera perennis is a perennial herb, roots fibrous; stems 20-60 cm tall, usually unbranched.
Leaves alternate, stalk to 0.7 cm long; blade 3-6 cm long, to 0.8 cm wide narrow, elliptic to widest above middle, tip blunt, base tapered to stalk, leafy bracts of inflorescence smaller.
Flowers yellow, petals 0.5-1 cm long, heart-shaped, notched at tip; calyx tube 0.3-1 cm long, lobes 0.4-0.6 cm long; blooming singly during the daytime, self-fertile; inflorescence nodding in bud, becoming erect as flowers bloom; blooms June-Aug.
Fruit dry, a capsule 0.4-1 cm long, 0.3-0.4 cm wide, 4-winged (Radford et al. 1968), elliptic to club-shaped, base tapered.
Wetland status: FAC-.
Frequency in NYC: Very infrequent.
Habitat: Moist to dry soil in undisturbed, open areas, meadows.