Oenothera parviflora is a biennial or brief perennial herb, 10-80 cm tall, very similar to O. biennis but stem rarely branches. Hairier than O. biennis, hairs having enlarged, swollen reddish bases.
Leaves alternate, stem leaves narrowly lance-shaped, somewhat fleshy and thickened. Upper leaves becoming leafy floral bracts, the lower flowers shorter than the bracts.
Flowers yellow, petals 4, 1-2 cm long; calyx tube 1.5-4 cm long, lobes 1-2 cm long; flower buds with appendages near tips of sepals projecting above bud 0.1-0.3 cm, not touching along edges and the base attached just slightly below the actual top of the calyx lobe; tips of inflorescence nodding; blooms and fruits July-Oct.
Fruit a dry capsule to 4 cm long.
Wetland status: FACU-.
Frequency in NYC: Very infrequent, or very infrequently recognized as different from O. biennis.
Habitat: Open, disturbed sites.