Oenothera biennis (Common Evening Primrose)
|Also known as:|
|Family:||Onagraceae (Evening Primrose)|
|Life cycle:||biennial, short-lived perennial|
|Habitat:||part shade, sun; fields, along roads, edges of woods, edges of streams|
|Bloom season:||July - October|
|Plant height:||2 to 6 feet|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Leafy spike of yellow flowers at the end of the stem, blooming from the bottom up, a few to several open at a time. Flowers are 1 to 2 inches across with 4 yellow heart-shaped petals and 8 yellow stamens surrounding a style with a cross-shaped stigma in the center. The stamens and style are typically shorter than the petals.
The 4 sepals behind the flower are ½ to 1¼ inch long and bend back away from the flower as it develops, pairs typically connected along one edge (connivent) until the flower opens, and are variously hairy, sometimes with glandular hairs. The calyx tube, connecting the ovary nestled in the leaf axil and base of the flower, is ¾ to 2 inches long and resembles a flower stalk. The flowers open in the evening and close up during the heat of the day.
Leaves and stem:
Leaves are up to 8 inches long and 2 inches wide, lance-elliptic, tapering to a point at the tip, slightly rough to the touch, hairless or with fine white hairs, toothless or with small teeth, and little or no stalk. Leaves tend to fold up some from the prominent central vein and edges are often somewhat wavy. Color is olive to light green and there are often small leaves sprouting from the leaf axils. The stem is stout, reddish or light green, covered in white hairs, and unbranched or branching.
A very common species, Common Evening Primrose is easily confused with the closely related Northern Evening Primrose (Oenothera parviflora). O. biennis usually has larger flowers but the sizes and other characteristics overlap in range between the two species so distinguishing them is difficult. For O. parviflora, look for a small ridge or knob at the tip end of the sepal, which O. biennis lacks, and more spreading hairs on the sepals. There are 2 varieties of O. biennis in Minnesota: var. canescens plants are more or less densely covered in appressed or curved hairs, few or none of which are glandular, var. biennis is more sparsely hairy with some gland-tipped hairs. It can grow into quite a robust plant in cultivation.
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Photos by K. Chayka taken in Ramsey and Lake counties. Photos courtesy Peter M. Dziuk taken in Anoka and Ramsey counties.
Have you seen this plant in Minnesota, or have any other comments about it?