Oenothera is a genus of about 160 species of herbaceous flowering plants native to the Americas. The genus includes the plants known as common evening primrose, narrow-leaved sundrops and white gaura. It is the type genus of the family Onagraceae. They are not closely related to the true primroses (genus Primula).
Description
The species vary in size from small alpine plants 10 centimeters tall, such as O. acaulis from Chile, to vigorous lowland species growing to around 3 meters talls, such as O. stubbei from Mexico. The leaves form a basal rosette at ground level and spiral up to the flowering stems. The blades are dentate or deeply lobed (pinnatifid). The flowers of many species open in the evening, hence the name "evening primrose". They may open in under a minute. Most species have yellow flowers, but some have white, purple, pink, or red. Most native desert species are white. Oenothera cespitosa, a species of western North America, produces white flowers that turn pink with age.
One of the most distinctive features of the flower is the stigma, which has four branches in an X shape.
Ecology
Evening primrose
Oenothera flowers are pollinated by insects, such as moths and bees. Like many other members of the Onagraceae, however, the pollen grains are loosely held together by viscin threads, so only insects that are morphologically specialized to gather this pollen can effectively pollinate the flowers. Bees with typical scopa cannot hold it. Also, the flowers open at a time when most bee species are inactive, so the bees which visit Oenothera are generally vespertine temporal specialists: bees that forage in the evening. The seeds ripen from late summer to fall.
Oenothera are used as food plants by the larvae of some Lepidoptera species, including the large white-lined sphinx (Hyles lineata). The flower moths Schinia felicitata and S. florida both feed exclusively on the genus, and the former is limited to O. deltoides.
