One factor to distinguish oenothera californica
(California evening primrose) from the similar oenothera deltoides
is the rather smaller leaves - often mostly hidden by the large petals; the deltoides species has leaves that are twice as long, projecting out beneath the flower head. Flowers of the California evening primrose are up to 3 inches in diameter, formed of four white, yellow-centered petals which fade to pink as they wither. In the middle are 8 stamens each terminated by a split anther. Like most members of this genus, flowers open in the evening. Flower buds point downwards. The stem becomes woody with age, and has peeling bark.