Sunday, June 10, 2018

Plant Story--Evening Primroses, Beautiful Whereever You Meet Them

evening primrose
There are 145 species of evening primrose, Oenothera, 80 of them native to the United States.While there are more different species in western North America, the common evening primrose, Oenothera biennis, can be found in all but the Rocky Mountain states.

Evening primroses have big flowers. If you find them open after 7 am or before 7 pm, the flowers are likely yellow. Night-flowering species are often white and close in daylight, so if you are to see them open you need to go out in twilight, wander with a flashlight or get up early. On a cloudy morning they stay open longer, but the white species tend to grow in drier places, where cloudy mornings are less common.
evening primrose, southern Wyoming
An evening primrose seen in southern Wyoming.

The common evening primrose Oenothera biennis is a tall plant--to just over 3'--of roadsides and disturbed sites all over North America. The specific epithet biennis translates from Latin as biennial. Biennial means the plant lives only two years. But biennial implies more. Most biennials grow without flowering their first year, throw all the stored energy of two years into flowers and seeds and then die. That's a monocarpic--single flowering period--life. (The alternate, the life history of most plants, is to be polycarpic, flowering more than once in a lifetime, often year after year). Thus the common evening primrose is a circle of leaves on the ground, a rosette, in its first year, forming a larger circle with each new leaf. The second year, a flowering stalk shoots upward, with leaves all along the stalk. It produces yellow flowers, the flowers develop into pods with seeds and the plant dies.
evening primrose
This is the general look of the common evening primrose
and the hairy evening primrose. 
In Colorado and the Rocky Mountain states, the hairy evening primrose, Oenothera villosa, formerly Oenothera strigosa, is a biennial very similar to the common evening primrose.

With so many species of evening primrose beyond those two, you can stumble on wonderful flowers.

This one was along the Devil's Backbone hiking trail in Loveland, Colorado on a morning in late May. It is Howard's evening primrose, Oenothera howardii.

Howard's evening primrose, Oenothera howardii
Howard's evening primrose, Oenothera howardii
Here is a close-up. This plant is a perennial. Notice that there isn't much of a stem on the flower. If there were two flowers they would grow separately from the base of the plant. Not surprisingly, this plant not very visible when it is not in flower.

Howard's evening primrose, Oenothera howardii
Howard's evening primrose, Oenothera howardii
Also inconspicuous unless it was flowering was the whitest evening primrose (USDA's common name) Oenothera albicaulis, also called prairie evening primrose and pale evening primrose. This is an annual that generally doesn't get very tall (to 15") and blooms at night. There was a population along the road west of Lake Keystone below Kingsley Dam north of Ogallala, Nebraska that I used to watch for. Some years I saw nothing, other years some early mornings there would be white flowers like stars along the road's edge.

white evening primrose

The plant below was seen in Arizona. It is probably Oenothera caespitosa, the dwarf evening primrose. They are perennials. The photo certainly shows how small evening primrose plants can be. The photo was taken in very early morning. 

Oenothera, Arizona

Here's another look that evening primroses have: nice stems and leaves below their big white flowers.This one was growing at lower elevations of Rocky Mountain National Park, Colorado.
evening primrose, Rocky Mountain National Park
evening primrose, Rocky Mountain National Park,
likely crownleaf evening primrose, Oenothera coronopifolia
And there are many yellow-flowered ones:
Missouri evening primrose
Missouri evening primrose, Oenothera missouriensis
I can name the one above because it is in my garden. Handsome evening primroses are available in the horticultural trade. In the Americas, if you plant ones that are native to your area, once established they should need no care. And you get spectacular flowers.

However, evening primroses are now found around the world. Looking for references on Google Scholar I find new reports of evening primroses published in the last four years for Spain, Bulgaria, Poland, Russia, Libya, the Punjab, and Anhui China, meaning the plants have escaped from cultivation and are spreading on their own across Eurasia. The species were Oenothera rosea, O. villosa, O. drummondii, and O. lacinata. The common evening primrose, Oenothera biennis, got to all those places in the 17th century, starting as a vegetable and garden flower and escaping to self-perpetuate in abandoned fields and roadsides. Here are three common evening primrose plants flowering as lawn weeds on Skeppsholmen Island, Stockholm, Sweden.

Oenothera biennis, Stockholm, Sweden

All over the world, watch for the beautiful evening primroses!


Comments and corrections welcome.

Previous post on evening primroses: Evening primroses--names and relations link
Missouri evening primrose

About monocarpic plants, ones that live several years, flower once and die. Century plants are a dramatic example link
flowering Agave


Kathy Keeler, A Wandering Botanist


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