The Evening Primrose's are generally known for flowers that close during daylight hours, although the flowers are usually partially open until noon, especially on cloudy days. Common Evening Primrose is an erect native biennial (or occasionally perennial) rising up to 6 feet in height on a usually unbranched stem. The stem is green with some reddish tones, ridged and usually has fine white hair.
The leaves are both basal and stem. Basal leaves taper to short stalks and form a rosette in the first year of growth. The stem leaves develop the second year when the flowering stem rises; they are alternate, lance-like, wavy edged, slightly toothed, slightly hairy on both surfaces, with one main central vein and fine laterals. They can be up to 8 inches long near the base and 1/4 as wide, but become considerable shorter near the top of the stem. Some leaves tend to have a twist at the tip. The upper leaves are sessile. There are usually much smaller secondary leaves showing in the leaf axils.
The inflorescence is a stiff, terminal flower spike of many flowers which open from the base of the spike and progress upward as the spike elongates. Short side branches in the inflorescence are not uncommon.
The flowers are 4-part, fragrant, from 3/4 to 2 inches wide with yellow corollas. They appear to have stalks but are really sessile. The corolla tube is quite long, slightly hairy, greenish with the ovary at the base next to the stem of the inflorescence. There is a small linear floral bract at the base of the tube. The petals are widest at the broad rounded tip, which has a slight notch. The bases are very narrow. There are four greenish-yellow sepals which are longer than the petals, very linear and reflexed back to the corolla tube when the flower opens. There are 8 stamens with yellow filaments and anthers, the anthers linear and quite long. The single style has a greenish 4-cleft stigma.
Seed: As the blooming flowers move upward, seed capsules, or pods, which are thicker at their base and about 1-1/4 inch long, form under them in a spiral pattern around the spike. These are stiff and hard, composed of 4 chambers (valves) and contain 300 to 400 very small reddish brown seeds per capsule (apprx. 90,000 to the ounce). The capsule opens at the top, seeds are dispersed by wind shaking the stem. Seeds can germinate in four weeks and will form a rosette, then the plant over-winters and flowers the following year. Seeds germinate best in cool soil and need light to germinate. If seeds are stored it should be in cold but dry storage. Cold moist stratification is not needed.
Habitat: Common Evening Primrose grows from a branching taproot and spreads via re-seeding. It prefers full sun, average moisture to dry (wet-mesic to dry) and well drained soil. It is adaptable to a number of sunny locations and will be found in fields, roadsides, abandoned areas, thickets and drier banks, etc.
Names: There are a number of similar species confusingly using the common name although those other species have available more appropriate names. The genus name Oenothera, comes from two Greek words, oinos for "wine" and thera for "to imbibe". This is an old name give by Theophrastus (371-286 BC) (a pupil of ARISTOTLE and the first important botanist of antiquity) to an unidentified plant, whose roots when eaten, were said to establish a desire for wine - others say it would do away with the effects of wine. The species name, biennis, refers to the biennial character of the plant. The author name for the plant classification - 'L.' is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. An older scientific name, still in use in Martha Crone's time is Oenothera muricata.
Comparisons: A much shorter Oenothera in the Garden is Prairie Sundrops, O. pilosella, which is not native to the state.
Below: 1st photo - There are 8 yellow stamens and a single style that has a greenish 4-cleft stigma (visible in photo and photo above). 2nd photo - The four sepals are long and linear and reflex back against the hairy corolla tube which is more densely hairy at its base, which is where the ovary is placed. A small green bract can be seen there also.
Below: 1st photo - The still partially open flowers of mid-morning. They will close soon. 2nd & 3rd photos - Seed Pods formed. Note - the flowers are not stalked, what appears as a stalk is the long corolla tube, the base of which contains the ovary and becomes the seed pod.
Below: 1st photo - Wavy-edge leaf structure. Note the small secondary leaves in the leaf axils. 2nd photo - The seed heads of October with open tips to release the many fine seeds by the wind shaking the stem. Note the spiral progression around the stalk.
Below: 1st photo - The stem is slightly ridged, green with reddish tints and soft whitish hair. 2nd photo - An upper stem leaf, mostly stalkless, one main central vein and a slight twist at the tip. 3rd photo - The underside of the leaf is more hairy than the upper surface, with longer hair on the main vein and shorter hair throughout the surface area.
Seeds of Common Evening Primrose: Seed capsules, or pods, are thicker at their base then at the top. These are stiff and hard, about 1-1/4 inch long, composed of 4 chambers (valves) and contain 300 to 400 very small reddish brown seeds per capsule. The capsule opens at the top, seeds are dispersed by wind shaking the stem. Seeds can germinate in four weeks and will form a rosette and overwinter and flower the following year.
Below: A historical photo of the Upland Garden with Common Evening Primrose blooming with Partridge Pea. Photo from a Kodachrome taken by Martha Crone on July 30, 1949. [Photo Courtesy Minnesota Historical Society, Martha Crone Collection.]
Notes: Common Evening Primrose is indigenous to the Garden area. Eloise Butler catalogued it on May 31, 1907. It was one of 4 Oenothera in the Garden at the time of Martha Crone's 1951 Garden census. She noted planting it in 1945 and '48. It is native to Minnesota in most counties with most of the exceptions being in the SW quadrant. It is found in most states and all the lower Canadian Provinces.
There are seven species of Oenothera found in Minnesota and all are considered native: O. biennis, Common Evening Primrose with two varieties; O. clelandii, Cleland's Evening Primrose; O. laciniata var. laciniata, Cut-leaved Evening Primrose; O. nuttallii, Nuttall's Evening Primrose; O. parviflora, Northern Evening Primrose, in two varieties; O. perennis, Perennial Evening Primrose; and O. rhombipetala, Rhombic (or Fourpoint) Evening Primrose.
Lore and Uses: There are medicinal uses of the plant recorded by Cherokee, Iroquois, Ojibwa and Potawatomi Native Americans. Densmore (Ref. #5) however does not record use of the plant by the Minnesota Chippewa (Ojibwa). Common uses were to make a poultice to treat bruises, a tea to use as a stimulant and the roots to treat skin eruptions. Generally, the drug in the plant acts as a sedative and as an astringent. The roots were also boiled and eaten like a potato.
The plant is grown commercially in a number of countries for the oil it produces, which oil contains fatty acids, linoleic acid and gamma linolenic acid (GLA). GLA is an essential fatty acid (EFA) in the omega-6 family and is sold as a dietary supplement. Linoleic acid is also a omega-6 fatty acid, is used in cooking oils and processed foods and converted to GLA in the body.
The flowers are attractive to Hummingbirds. Seed pods provide winter bird food. HOWEVER - if you have Japanese Beetles in your vicinity - this is one of their favorite plants.
Eloise Butler wrote this about the plant: "Who has not seen a tall, stout weed with a long dense spike of sweet-scented flowers with rather large, deflexed, yellow petals? But how many take the trouble to know its name, Oenothera biennis, or Common Evening Primrose? The flowers are succeeded by stiff, four-valved pods splitting at the top, from which the seeds are threshed out by the wind. The seeds that sprout will form a rosette lying flat on the ground and made up of row upon row of oblong leaves narrowed at the base and becoming shorter and shorter above and towards the center - a fine example of one of the methods of preventing overshading. The rosette has varied autumnal tints and survives the winter to form, from a central bud, an erect flowering stalk that often branches like a candelabra, and completes its course when the seed is ripened. Such plants are biennials like many garden vegetables, cabbage, beet, etc. In flower, this weed decorates the roadside." Published 17 September 1911. Minneapolis Sunday Tribune.
Poet John Clare, English (1793- 1864) Wrote a poem titled "Evening Primrose"
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"