The Evening Primroses are generally known for flowers that close during daylight hours. The species that are referred to as "Sundrops" have flowers open during the day. Prairie Sundrops is a shorter erect perennial forb, growing to 1-1/2 feet high on green to greenish-red stems that have long hairs. Stems may tend to recline as the plant flowers.
The leaves are alternate, mostly without stalks, lance-shaped, with smooth to slightly toothed margins and fine hair on both upper and lower surfaces and margins.
The inflorescence is a dense short spike held at or above the leaves.
The flowers are 1-1/4 to 2 inches wide when open and appear to have a long stalk, but that is the corolla tube which has the ovary at the base, where there is also a small, linear floral bract. The 4-part flowers have large ovate yellow petals, broader near the tip, base narrowed. These have a notch at the tip. There are four green sepals. The flowers are perfect with 8 stamens that have yellow filaments and long yellow anthers that are held almost perpendicular to the filament. The pollen turns reddish as the flower matures. The ovary has a single style but with a 4-cleft stigma that looks like a "cross" shape.
Seed: An elliptical seed capsule forms after the flower fades; the capsule tapers toward the base, unlike the Common Evening Primrose O. biennis L. where it enlarges. When mature, the capsule opens at the tip allowing the numerous small, light seeds (apprx. 266,000 to the ounce) to be dispersed by wind shaking the stem. Seeds should be sown in a warm location and if stored, they should be kept in cold dry storage.
Habitat: Prairie Sundrops grows from a rhizomatous root system, which allows the plant to spread and form colonies. It does best in full sun, richer soils and wet mesic to dry mesic moisture conditions. Lack of full sun usually results in prostrate stems. While still found in the wild in some states, it is primarily grown as an ornamental. A century ago it was quite popular for that and is a beautiful addition to a garden.
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 found, when eaten, and were said to establish a desire for wine - others say it would do away with the effects of wine. The species name, pilosella is from pilosus for "hairy" and from ella for "a little" meaning "a little hairy, referring to the hairs on the plant stem. The author name for the plant classification - ‘Raf.’ is for Constantine Samuel Rafinesque, (1783-1840), European polymath who traveled in the United States, lived here many years, collected specimens, and published over 6,700 binomial names for plants. He applied to be botanist on the Lewis & Clark expedition but Jefferson turned him down in favor of training Lewis to act as botanist and saving the expense of another person.
Comparisons: The Evening Primrose family has showy yellow flowers rising from the axils of leafy bracts at the top of the stems. Flowers have yellow petals and an elongated calyx tube. A much taller Oenothera in the Garden is Common Evening Primrose, O. biennis, which is native to the state.
Above: This grouping of Sundrops was in bloom during the last half of June.
Below: The lines on the yellow petals are nectar guides for insects. Note the yellow stigma of the pistil that is 4-cleft, forming a cross.
Below: All the upper parts of the stem and flower are hairy except the yellow petals. At the base of the open flower are the decaying sepals. The yellowish green floral tube leads down to the separated green ovary which is subtended by a green hairy bract.
Below: The leaves have a hairy surface and margins both upperside (1st photo) and underside (2nd photo).
Below: A historical photo of the old Garden Office with Prairie Sundrops blooming in front. Photo from a Kodachrome taken by Martha Crone on June 23, 1949. (Photo Courtesy Minnesota Historical Society, Martha Crone Collection.)
Notes: Prairie Sundrops is not indigenous to the Garden area but was listed on Martha Crone's 1951 inventory of plants in the Garden at that time under the name "Meadow Sundrops" or Oenothera pratensis which today refers to this plant - O. pilosella. Its not clear when it first arrived in the Garden, but Martha noted it in bloom in 1938 and noted planting it in 1946. A photo of the Garden Office taken in 1949 shows an extensive planting in the front of the office. Not native to Minnesota - introduced here as well as in in neighboring Wisconsin. Its native range in North America is generally east of the Mississippi River in the U.S. excluding the SE Atlantic coast states and in Canada it is known in Ontario and Quebec.
There are seven species of Oenothera found in Minnesota that 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.
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"