Wild Flowers of Pittsburgh

Evening Primrose (Oenothera Biennis)

A tall and stately weed whose flowers we almost never get to see in their full glory. It’s a night-bloomer, opening at dusk and fading in the early hours of the morning. These pictures were taken shortly after sunrise at the edge of a parking lot in Beechview, where Evening Primroses were blooming in the middle of August.

Flowers. Pale yellow; four broad petals; cross-shaped anther in the middle; borne in branching racemes.

Leaves. Lanceolate, sessile, slightly toothed; net-veined, with center rib often reddish toward base; alternate; thick on the stem, with branches or abortive branches in axils; mostly smooth.

Stem. Stout; somewhat sticky; woody below, with dark brownish stripes; to 6 feet or more; much branched.

At one time this plant was placed in a genus Onagra, from which the family Onagraceae was named; but Gray and most modern botanists make that genus part of Oenothera.

Gray describes the genus and the species:

OENOTHERA L. EVENING PRIMROSE. Calyx-tube prolonged beyond the ovary, deciduous; the lobes 4, reflexed. Petals 4. Stamens 8; anthers mostly linear and versatile. Capsule 4-valved, many-seeded. Seeds naked or with an obscure membranaceous crest. — Leaves alternate or rarely all basal. Flowers yellow, white, or rose-color. (An old name of unknown origin, for a species of Epilobium.)

§ 1. ONAGRA (Adans.) Ser. Stigma-lobes linear, elongated; flower-buds upright; petals yellow; fruit subcylindrical, elongated; seeds in 2 rotos in each cell; caulescent annuals or biennials.

O. biennis L. (COMMON E.) Rather stout, erect, 3-15 dm. high, usually simple, more or less spreading-pubescent to hirsute; leaves lanceolate to oblong or rarely ovate-lanceolate, repandly denticulate, acute or acuminate; bracts lanceolate, shorter than or scarcely exceeding the capsules; calyx-tube 2.5-3.5 cm. long; petals yellow, obovate, 1.5-2.5 cm. long; pods more or less hirsute, narrowed almost from the base, 2-3.5 cm. long. (Onagra Scop.) —Open places, common.

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