The Evening Primrose Family consists of herbs usually with simple leaves. The flowers have 4 petals and most commonly, 8 stamens. The stigma is either ball- shaped or 4-lobed. The ovary is inferior.
The name is misleading, for these plants are not related to the Primroses (Primulaceae). John Parkinson, an English herbalist who was the first to describe these New World flowers, gave the Primrose name to them in the early 1600’s. Their scent reminded him of the Wild Primroses in English meadows. The "Evening" of the name refers to the habit of some species of opening at sundown and closing by morning. (Dale 139).
About 600 species of wide distribution especially in western North America. (Munz, Flora So. Calif. 589).