Common Evening Primrose

(Oenothera biennis)

Common Evening Primrose (Oenothera biennis L.)

Identification: Flowers yellow, large (1 to 2 inches in diameter), with 4 petals and 8 stamens. Stigma with 4 lobes, cross-shaped. Calyx with 4 sepals, the sepals bent downward (reflexed). Flowers buds completely covered and enclosed by the sepals. Seed capsules narrow, elongate, ridged, sessile to the stem in the leaf axils. Stem usually branched, tinged with dark red. Leaves crowded on the stem, elongate, narrow, and with ragged outer margins. Plant 1 to 5 feet in height.

Distribution: Throughout most of North America.

Habitat: Common Evening Primrose is typically found on dry soils and in open areas such as empty lots, roadsides, and fields.

Flowering period: June to September.

Similar Species: Common Evening Primrose is very difficult to separate from Small-flowered Evening Primrose. The flowers of Small-flowered Evening Primrose are usually smaller (about 1 inch in diameter). The stem is not as heavily branched. The flower bud of Common Evening Primrose is completely encased by the sepals, but the sepals of Small-flowered Evening Primrose are usually slightly spread with the yellow of the petals showing through.

Comments: The flowers of Common Evening Primrose open in the early evening and wilt by noon of the following day.