Evening Primroses of genus Oenothera are annual to perennial herbs with alternate or basal, simple to pinnately lobed leaves. The flowers are white or yellow, frequently aging to reddish or purplish, often nocturnal, sometimes fragrant, usually arranged in leafy to bractless spikes or elongated clusters, or stalkless among the basal leaves. The elongated floral axis below the calyx is often very conspicuous. The 4 sepals are mostly separated, bent backward, sometimes joined and turned to one side in flowering time. The 4 petals are narrowed at base, stalkless, often notched with rounded points to shallowly notched. There are 8 stamens, with the anthers usually being linear and attached near the middle, sometimes attached close to their base. The stigma has 4 linear lobes. The fruit capsules are woody to membranous, straight to curved or partially coiled, splitting open, 4-celled. The numerous seeds are not hair-tufted. The genus consists of about 50 species worldwide, all but one in N. or S. America. The name comes from the Greek name used by Theophrastus.
Guide to Identify Presented Species of Genus Oenothera
FLOWERS WHITE OR LIGHT PINK
O. cespitosa Tufted Evening Primrose Tufted, almost stemless perennial rarely up to 25 cm tall. Dry, bare hills.
Flowers white to pink, 5-9 cm wide, single from the base, open in the evening.
Leaves basal, oblanceolate, entire or toothed, 10-25 cm long, 1-2.5 cm broad.
O. villosa Hairy Evening Primrose Robust biennial with hairy stems, 30-100 cm tall. Dry, moderately open sites.
Flowers fragrant, bright yellow, 3-4 cm wide, in a tall cluster, with 4 broad petals.
Leaves alternate and basal, lance-shaped, numerous, entire to wavy-toothed.