By late February, the spent stems of many herbaceous plants are beginning to fall to the ground and break down, adding to the nutrients in the soil, or making nesting material available for birds and other animals. Evening Primrose (Oenothera biennis) is an exception, with stems still upright, and fruit capsules still dispersing seeds – via wind, or scattered on the ground near parent plants.  Evening Primrose is a biennial, a characteristic reflected in its scientific name, ‘biennis’.  This means that it typically lives only two years, the first as a ground-level rosette of leaves.  If it gathers enough energy, the second year of life it will bloom, develop fruits, and die.  Replacing the parent plant with offspring in the same location is a good evolutionary strategy for the plant.

Evening Primrose (Oenothera biennis) fruit capsules

Not all seeds are destined to grow into another Evening Primrose plant, since some will become a snack for hungry birds. Evening Primrose can afford this loss.  There are plenty of seeds, with potentially hundreds produced by each fruit capsule.

Eastern Goldfinches eat Evening Primrose seeds.

Evening Primrose can be found throughout most of the United States (some Rocky Mountain states are an exception) and Canada, blooming from late June through much of the fall, often in disturbed areas.  ‘Evening’ in this plant’s name refers to the fact that the flowers open late in the day, usually blooming from dusk until the early morning hours, although they may stay open longer on cloudy or overcast days.

Evening Primrose in bloom

Plant species that bloom at night have generally evolved to partner for pollination services with an animal that is active at night, usually moths or bats. The flowers are fragrant, which is another characteristic of night blooming plants.  Many moth species can detect fragrances from long distances, and will follow the fragrance to find their nectar reward.  Moths, particularly some sphinx moths, are among Evening Primrose’s pollinators.

During those daylight hours that the flowers are open, butterflies may drink nectar from Evening Primrose flowers.

Little Glassywing drinking nectar from an Evening Primrose flower.

Many bee species also visit the flowers, including some that specialize on Evening Primrose and other related species.

Sweat Bee, probably Lasioglossum oenotherae, on Evening Primrose

Sweat Bee, probably Lasioglossum oenotherae, harvesting pollen from Evening Primrose. These bees have evolved scopa that are efficient for handling Evening Primrose’s stringy pollen.

Some of these specialists are able to fly in dim light during dusk and dawn, and even into the night when there is enough moonlight. In addition to the large compound eyes on each side of their faces, bees have ocelli, simple eyes at the top of their heads.  Ocelli help the bee in positioning and orientation, with the aid of light from the sun or even a full moon. These specialist bees are aided by larger ocelli than the typical bee, so they can function in low light.

Sweat Bee, probably Lasioglossum oenotherae, on Evening Primrose. These bees evolved scopa on their hind legs that are efficient for carrying Evening Primrose’s stringy pollen. Look for the ocelli (eyes) at the top of its head. They look like little dots.

Caterpillars of several moth species feed on the leaves or flowers of Evening Primrose.

Yellow Bear (Virginian Tiger Moth) caterpillar on Evening Primrose

For human consumers, the young leaves, flowers, shoots and first year roots of Evening Primrose are edible, with the proper preparation. The leaves and roots are thought to have a peppery taste.   Evening Primrose is cultivated for its oil, which contains some essential fatty acids (Omega-6 fatty acid, linolenic acid and gamma-linolenic acid). Evening Primrose oil has been licensed in several countries for treatment of eczema and breast pain.  Native Americans used it to treat a broad range of ills.

Evening Primrose (Oenothera biennis)

Look for Evening Primrose fruit capsules now,

Evening Primrose (Oenothera biennis) fruit capsules

and watch for new plants blooming at nearby locations this summer.

Evening Primrose (Oenothera biennis) in bloom

Resources

Foster, Steven; Duke, James A. A Field Guide to Medicinal Plants and Herbs of Eastern and Central North America.  2000.

Peterson, Lee Allen. A Field Guide to Edible Wild Plants of Eastern and Central North America. 1977.

Wagner, David L.; Caterpillars of Eastern North America, 2005.

Wilson, Joseph S.; Carril, Olivia Messinger. The Bees in Your Backyard. 2016.

Illinois Wildflowers

Discover Life

USDA Plant Database

Mayo Clinic