by Jane Thomson
Each spring, I hike trails in the northern Front Range of the Colorado Rockies with a group of fellow wildflower enthusiasts. This spring, much of the western U. S. had been suffering from severe heat and drought. However, the northern part of the Front Range, as locals call Colorado’s eastern foothills, had been blessed with unusually cool temperatures and drenching rains. As a result, wildflower displays were the best seen in years. Flowers were bigger, and plants were much taller than usual. Wild evening primroses are one of the delights of this display.
Evening primroses are in the genus Oenothera, and their flowers can be recognized because they have four petals, four or eight stamens, and a stigma with four terminal parts. The picture above shows one of this year’s flowers on steroids, O. howardii, Howard’s evening primrose. Note the size compared to the handle portion of the hiking pole. Its flower measures more than four inches across. Spent flowers in this species fade to a copper orange (inset). Another yellow evening primrose found in a dry, sandy area is O. lavandulifolius, lavender-leaved evening primrose (see below). Its species name was chosen because of leaves similar to those of lavender plants.
Oenothera species are believed to have originated in Mexico and Central America, although they have now spread from North to South America. Many species form hybrids with one another. As a result, their appearance is now quite variable, with heights ranging from four inches (alpine) to ten feet (Mexico) and leaves that can be entire, toothed, lanceolate, or ovate. Flower colors also vary widely and can be yellow, white, pink, purple, or red. However, the most common colors in our area are yellow and white, with white flowers typically found in dry, desert habitats.
One white evening primrose that we often see out hiking is O. coronopitifolia, cut leaf evening primrose, which can be identified by its deeply divided leaves (see inset). Another characteristic is that its flowers turn pink with age.
Sometimes evening primroses are hard to identify because flowers open late in the day. This is because they have evolved in sequence with their main pollinators, nocturnal moths. Typically their flowers begin to wither and close in the sun the day after flowering. The plant below, O. cespitosa, tufted evening primrose, shows flower buds that are only partially open. Often at the start of a hike, we find evening primroses aren’t open yet, and we see them to better advantage on the way home.
This primrose is one of four varieties of tufted evening primroses in Colorado. Which one? We’ll leave that to the experts. Do you find any evening primroses growing wild in your area? It is fun to see how many you can identify out on the trail or scattered here and there in fields near where you live.
Photo Credits: 1) O. howardii, Howard’s evening primrose, Coyote Ridge Natural Area (inset photo by Ed Seely, Pineridge Natural Area); 2) O. lavandufolia, lavender-leaved evening primrose, Pawnee Buttes National Grassland, Weld County, CO; 3) O. coronopitifolia, cut leaf evening primrose, Eagle’s Nest Open Space; 4) O. cespitosa, tufted evening primrose, Hermit Park, Limber Pine trail. All photos taken in Larimer County, CO by the author, except as noted.
Ackerfield, J. 2015. Flora of Colorado. Brit Press.
Bilsing, L. (ed.). 2017. Wildflowers and other plants of the Larimer County foothills region, 2nd ed. Larimer County Department of Natural Resources.
Elpel, T.J. 2010. Botany in a day, 5th ed. HOPS Press, LLC.
Oenothera. Accessed 8/28/2021. wikipedia.org/wiki/Oenothera
Jane Thomson has been a member of the Herb Society of America for over 20 years, first with the Sangre De Cristo Unit in Santa Fe and currently with the Rocky Mountain Unit. She is a retired chemist and amateur wildflower enthusiast.