365 Urban Species. #233: Evening Primrose

Photos by urbpan. Location: Charles River, near the Mass Ave Bridge, Boston.

Urban species #233: Evening primrose Oenothera biennis

Ignore a weed long enough, and eventually it may reward you with beautiful flowers. That's the lesson I learn each year from evening primrose. Particularly at work, where coworkers dislike the unkept appearance of tall weeds around buildings and cages, I have to lobby for leaving the wild plants intact. Evening primrose is a biennial, growing a low rosette with no flowers in its first year. Its second year it bolts upward early in the summer, and can keep growing until it's five feet tall or more. But it's not until around now, as the days begin to shorten again, that its many yellow blossoms open.

Each four-petaled flower bears a clearly evident cross-shaped stigma. The flowers open in the evening, and close before noon. Like most night-blooming flowers (such as white lychnis) evening primrose is pollinated by moths, specifically sphinx moths. (Other night-blooming flowers, such as some cactus species, are pollinated by bats.) Hover flies, and butterflies visit it in the morning hours. Evening primrose fruits persist on the dry stalk of the plant through winter, feeding a variety of finches deft enough to pick them out.

Evening primrose was originally native to the plains states, but the clearing of forests, and the movements of birds and humans have allowed it to naturalize in all but some of the Rocky Mountain states. Native Americans used evening primrose root for medicinal purposes, and the modern herbal medicine movement prizes the plant for many different uses. It's nice to see the tall weed at the edge of the buildings get some respect.



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