The tufted evening primrose (Oenothera caespitosa) is a perennial plant that blooms from September through April. The flowers are about three inches wide with four white, heart-shaped petals and yellow stamens. The flowers, which are very fragrant, open in late afternoon, close the next morning, and wither to pink or red-violet. Sometimes the flowers are bright yellow. According to the U.S. Forest Service, “the flowers often have a long floral tube that holds the petals well above the base of the flower. Nectar collects in the base of the tube so only long-tongued visitors can get a nectar reward.
This plant occurs throughout the western United States and favors roadsides and dry rocky slopes from grassland to pine forest clearings. The plant gets about one foot tall.
The main pollinators are hawk moths. See this page for photos and information about hawk moths from the U.S. Forest Service. Hawk moths have very long tongues.
The flowers are also visited by hummingbirds in the morning.
These primroses can be used in gardens but they must be protected because javelinas and rabbits like to browse on this plant. Many birds eat the seeds. Foliage can be pruned to the ground during summer dormant period.
USFS notes that “This plant is showy, grows in poor soils, and requires little water, which makes it a perfect candidate for western xeriscape gardens.”
The tufted evening primrose is unrelated to the primroses of Europe. According to the University of Texas, “Apparently in the early 1600s when an eastern United States species of Oenothera was being described, its sweet scent reminded the botanist of wild primroses of Europe. He gave the name to those plants and it stuck.”
Primrose oil, derived from the seeds of various species of Oenothera, has long been used in folk and “alternative” medicine to treat various conditions. (See Chinese and American Indian uses.) However, there is little evidence that primrose oil is effective in treating any condition according to Drugs.com. WebMD opines that primrose oil is “possibly effective” for treating nerve damage caused by diabetes. That WebMD link also provides a long list of other conditions for which treatment with primrose oil is “possibly ineffective” and another list of conditions for which there is “insufficient evidence.”
See more photos from the Arizona-Sonora Desert Museum digital library.