Tufted Evening Primrose
One evening in late May, bundled up like it was mid-February, I wandered around the Rims area of Billings in search of native plants. It’s hard to imagine that the sandstone comprising the Rims was once a barrier island in the subtropical environment of the Western Interior Seaway. No one could possibly confuse today’s cold, semi-arid climate with the sub-tropics. It’s a climate of extremes: blazing heat in the summer, bone-chilling cold in the winter, an annual precipitation of less than 20 inches, and the ever-present wind.
Climate defines soil, which on the Rims can be little more than weathered sandstone and siltstone fragments littering the bedrock surface. Like soil, climate also defines plant communities. Although a cold, dry climate with poorly developed soils may not typically be associated with plant diversity, it’s filled with hardy souls. Nature adapts and is full of surprises, and it is pure delight to see clumps of Oenothera caespitosa, or tufted evening primrose, in full bloom among the jumble of boulders, or sometimes, growing directly within the cracks of the rock. This treat is always worth the price of admission, which on this May day was snow squalls and icy-cold wind.
Tufted evening primrose is one of the loveliest native plants found in dry climates across western and central North America. Its botanical name translates to “wine seeker, densely clumped,” which is apt for a low-growing, mounded plant with very fragrant, citrus-scented flowers. Everything about this plant—its physical structure, leaf shape and size, and bloom shape and time—are adapted to conserving energy and water, maximizing photosynthesis and pollination, and protecting it from wind and temperature extremes in the harsh arid climate where it first evolved tens of millions of years ago, Mexico’s Sierra Madre.
It’s a night-blooming plant, growing up to seven inches tall and a foot or more in diameter. This mounding structure protects it from the wind and cold, and also shades the soil to conserve moisture during the heat of the day. The leaves are long and narrow, wider at the tip than the base, providing plenty of surface area for photosynthesis and protection from the harsh climate. Its grayish, bluish-green leaves are covered with a soft-to-the-touch white “fuzz” that conserves moisture.
Although the plant is quite interesting in itself, its luminescent white flowers, like the stars, are jewels of the night. They are large, two to four inches in diameter, with four heart-shaped petals joined together at the base, forming a cup. The eight bright-yellow stamens provide strong contrast against its white petals. Depending upon a plant’s size, there can be as few as three or four or well over 20 flowers blooming at the same time.
The flowers begin blooming in late afternoon or early evening, just in time for the arrival of the white-lined sphinx moth, upon which the tufted evening primrose depends for pollination. When direct sunlight hits the flowers the following day, they close, turn pink, and wither. Although an individual flower’s beauty is all too ephemeral, the long bloom season, May through July, ensures plenty of viewing opportunities. On a warm, soft, moonlit summer’s evening there is no better sight than tufted evening primrose in full bloom and the accompanying dance of white-lined sphinx moths.
The good news is you don’t have to be in the Rims area to see these flowers. They are found across Montana in dry soils, especially along backroads. You can even enjoy this plant in your garden; all it requires is dry soil. Plant it. The white-lined sphinx moths will follow, and you can sit back and watch the show. You will not be disappointed.
Today’s Field Note was written in the Field Notes Writing Workshop at the Montana Natural History Center. I’m Deb Drain for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. To find out about upcoming events and programs at the Center, call 406.327.0405, or visit our website at MontanaNaturalist.org.