Common Evening Primrose

Oenothera biennis

ee-no-THEE-ruh  by-EN-iss

As of 12-21-23 when this page was last updated, Plants of the World Online lists a whopping 127 synonyms of Oenothera biennis. Including them all here would take up a lot of space, but you can see them by clicking HERE. 

Oenothera biennis L. is the accepted scientific name for the Evening Primrose. Both the genus and species were named and described as such by Carl von Linnaeus in the first volume of the first edition of Species Plantarum in 1753. 

As of 12-21-23 when this page was last updated, Plants of the World Online lists 157 species in the Oenothera genus. It is a member of the plant family Onagraceae with 22 genera. Those numbers could change as updates are made on POWO.

The above distribution map for Oenothera biennis is from Plants of the World Online. Areas in green are where the species is native and purple is where it has been introduced. The map on the USDA Plants Database for the United States and Canada is similar.

The map on iNaturalist shows where members have made observations. Anyone can join and it is a great website to confirm and share your observations. The maps on iNaturalist are continually updated as members post new observations.

THERE ARE SEVERAL LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING AND TO HELP WITH A BETTER POSITIVE ID.

When I moved back to the family farm in west-central Missouri in 2013, I noticed this plant coming up in the cracks in the floor of what used to be the back porch of my grandparent’s old house. My dad said it always comes up there every year. I let it grow so I could figure out what it was. Well, it grew and flowered but normally they were always closed by the time I got up and went outside. I was able to identify it as Oenothera biennis, the Evening Primrose, from photos on the Missouri Plants website.

It is odd I haven’t seen the Oenothera biennis growing anywhere else on the farm or even along back roads. They spread like crazy! I guess perhaps I am looking at flowers while wildflower hunting and maybe I just haven’t noticed them. It has always been strange to me how some species just pop up and do well in certain areas.

Oenothera biennis is a biennial species, sometimes annual, that is native throughout most of North America. In some areas, it is quite common while it is sparsely found in others. Its preference is full sun in a variety of habitats and is even used in wildflower gardens. It may prefer somewhat sandy soil, but other types are sometimes acceptable. In my experience, it is very drought-tolerant and rarely receives supplemental water. 

The Missouri Plants website lists 12 species of Oenothera found in Missouri.

Being a biennial, it sends up a rosette of leaves the first year and a long stem with flowers the second. The plant dies once it sets seed. The flowers of Oenothera biennis begin to open at dusk and close in the morning once it receives bright sun. For me, that is before I get up… 

Oenothera biennis can grow to around 6’ tall in optimum conditions with one or more stems, branched or unbranched. The light green or red stems are densely hairy (pubescent) with a combination of long and short hairs. The short hairs are appressed to upward curving while the longer hairs can be loosely appressed or spreading. 

The light green lance-shaped leaves grow up to 8” long a 2” wide and grow in an alternate pattern along the stem. Leaf margins are smooth to irregularly toothed (dentate) and sometimes lobed toward the base. The leaves can have short petioles (leaf stalk) or be sessile (no petiole) and have very short-appressed or curved hairs. There could be smaller secondary leaves growing from the axils of leaves at the nodes. Several species of caterpillars feed on the leaves.

My thanks to Pamela Trewatha of the Missouri State University for allowing me to use her photo from Midwest Weeds and Wildflowers. I will replace it with my own if I can get up early enough…

Panicles of yellow flowers grow from the ends of stems or branches. Each flower has 4 petals that are broadly ovate or broadly heart-shaped and have prominent stamens and a 4-lobed stigma. There is a long floral tube, that looks more like a flower stalk (pedicel), with the ovary below that. Below the corollas (petals) is the calyx which normally encloses the petals. With this one, they bend backward… The page on the Missouri Plants website gives a great description with a well-detailed photo.

The flowers are pollinated mainly by nocturnal moths, such as the Sphinx Moth. Hummingbirds and bees feed on the nectar when the flowers are open in the morning if they get a chance. 

The Oenothera biennis has REALLY spread over the past few years.

Once flowering is completed, they are replaced by fruit/seedpod. Seedpods are fairly long and split open (longitudinally dehiscent) to release the seed. The seeds are dark brown to nearly black and are so tiny they can be dispersed by the wind. Information indicates the seeds remain viable for over 70 years! Information says Goldfinches eat the seed…

The above photo taken on March 20 in 2022 shows how the fruit splits open to release the seed.

The above photo shows a rosette of first-year plants. At least I think they are first-year plants… We’ll see what happens… Maybe this is their second year and they are getting an early start.

The summer of 2023 was very hot and dry and most of the wildflowers on the farm had burned up by mid-summer. I photographed a few wildflowers around the yard and in the garden because there was no point in walking through the hayfield and pastures. Of course, as always, the Oenothera biennis were growing in the cracks on the old back porch floor where my grandparent’s home was.

Then, on September 24 in 2023, I was wildflower hunting in the south hayfield and spotted a single Oenothera biennis. It was the first time I found any growing anywhere besides around the old foundation where my grandparent’s old home was.

What was even stranger was the plant still had flowers at almost 6 PM! I thought it was maybe a different species of Oenothera, but it was definitely Oenothera biennis…

I have enjoyed photographing and learning about the many wildflowers growing on the family farm and in other areas. The farm is in Windsor, Missouri in Pettis County (Henry County is across the street, and Benton and Johnson aren’t far away). I have grown over 500 different plants and identified over 200 species of wildflowers (most have pages listed on the right side of the page). I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can be somewhat variable from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky.

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
USDA PLANTS DATABASE
USDA PLANT GUIDE
DAVE’S GARDEN
MISSOURI PLANTS
MISSOURI BOTANICAL GARDEN
MSU-MIDWEST WEEDS AND WILDFLOWERS
MISSOURI DEPARTMENT OF CONSERVATION
iNATURALIST
WILDFLOWER SEARCH
ARKANSAS NATIVE PLANT SOCIETY
FRIENDS OF THE WILDFLOWER GARDEN
ILLINOIS WILDFLOWERS
MINNESOTA WILDFLOWERS
KANSAS WILDFLOWERS AND GRASSES
NORTH CAROLINA STATE UNIVERSITY
PFAF(PLANTS FOR A FUTURE)
GO BOTANY
LADY BIRD JOHNSON WILDFLOWER CENTER
FLORA FINDER
MARYLAND BIODIVERSITY PROJECT
GARDENIA
OHIO PERENNIAL AND BIENNIAL WEED GUIDE
UNIVERSITY OF WASHINGTON-BURKE HERBARIUM

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. Some websites have hundreds and thousands of species to keep up with. Accepted scientific names change periodically and can be hard to keep with. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is one of the most reliable and up-to-date plant databases and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos but I do get behind. We are all a work in progress. 🙂