Stems stout, wandlike and simple or somewhat branched, 1 to 6 feet high from a biennial root. Stems and leaves somewhat hairy. Leaves lanceolate to ovate-lanceolate, sessile, 2 to 6 inches long, the lower ones with petioles, the upper ones much reduced in size; margins with low, distant teeth. Flowers in the axils of the reduced upper leaves (or bracts), bright yellow, 1 to 2 inches broad in terminal spikes, opening in the evening; calyx tube slender, two or three times longer than the ovary, its four slender lobes reflexed; petals four, broadly obovate; stamens eight, equal in length, the linear anthers on threadlike filaments. Fruiting capsules oblong, narrowed toward the apex, three-fourths to 11/2 inches long and longer than the upper leaves (or bracts), one-eighth to one-fourth of an inch thick.
A. Common Evening Primrose - Oenothera biennis
Dry or sandy soil in fields, waste ground and along roadsides, Labrador to Minnesota, south to Florida and Texas. Flowering from the latter part of June until autumn. Often appearing like a weed.
The Evening Primrose is a variable species and consists of several races or mutants which have been regarded as valid species. There are also two other closely related species in addition to the next one which is described. They are the Small-flowered Evening Primrose (Oenothera cruciata Nuttall), with linear-lanceolate calyx segments and linear petals, one-fourth to one-half of an inch long, found usually in sandy soil from Maine and Massachusetts to northern New York; and Oakes's Evening Primrose (Oenothera oakesiana Robbins), a dull-green plant covered with a soft, appressed pubescence, rather large flowers with linear-lanceolate calyx segments and obovate petals one-half to three-fourths of an inch long. Frequent in sandy soil in southern New England, Long Island and Eastern New York.