hairy evening primrose

Hairy evening primrose is a common and widespread flowering plant. There are two subspecies of Oenothera villosa, both share the common name with the parent species hairy evening primrose, and both occur in Minnesota. The eastern subspecies Oenothera villosa ssp. villosa is by far the most common subspecies in Minnesota.

Hairy evening primrose (ssp. villosa) is native to North America. In the United States it occurs in every state from the East Coast to the foothills of the Rocky Mountains. It occurs across southern Canada from Nova Scotia to British Columbia. It has been widely introduced worldwide in the temperate regions of Europe, Asia, southern Africa, and southern South America. It is found in a variety of open habitats, including prairie hillsides, forest openings, open woodlands, lake shores, and stream sides. It is often found in disturbed areas, including abandoned fields, roadsides, railroads, and ditches. It grows usually in moist soil.

Hairy evening primrose (ssp. villosa) is an erect, biennial, 20″ to 80″ (50 to 200 cm) tall, herbaceous forb. In the first year it forms a rosette of basal leaves. In the second year it sends up one to several flowering stems from a taproot and a fibrous root system. It dies after bearing fruit once. The overall color is dull grayish green.

Basal leaves are narrowly inversely lance-shaped to inversely lance-shaped, 4″ to 12″ (10 to 30 cm) long, and usually ½″ to 1½″ (12 to 40 mm) wide, sometimes wider. They are usually tapered at the base to the leaf stalk (petiole), but they are occasionally rounded at the base. The upper surface is grayish green to dull green. The upper and lower surfaces are moderately to densely covered with short, appressed, nonglandular hairs. Occasionally the hairs are loosely ascending, shaggy. The margins are sparsely to moderately toothed, and there are sometimes a few lobes near the base.

The stem is erect or strongly ascending, and it may be branched or unbranched. It is densely covered with short, appressed to upwardly curved, nonglandular hairs. It sometimes also has longer, loosely appressed to spreading, nonglandular hairs that have a small blister (pustule) at the base. The hairs give the stem a grayish appearance.

Stem leaves are alternate, 2″ to 8″ (5 to 20 cm) long, and usually ⅜″ to 1″ (10 to 25 mm) wide, sometimes much wider. Lower stem leaves are similar to the basal leaves. The veins are prominent, especially on the underside, and they are usually pale green, rarely red. As the leaves ascend the stem they become narrowly lance-shaped to lance-shaped and shorter stalked to stalkless, and the margins become sparsely to moderately toothed.

The inflorescence is an erect, unbranched, relatively dense spike terminating the stem.

Each flower is subtended by a persistent, leaf-like bract. What appears to be a stalk is, in fact, an elongated ovary surmounted by a hypanthium, a floral tube formed by the fused bases of the sepals, petals, and stamens. The ovary is sparsely to densely covered with short, appressed, nonglandular hairs, and sparsely to densely covered with longer, spreading, nonglandular hairs with red pustular bases. The floral tube is green to yellowish green and ⅞″ to 1¾″ (23 to 44 mm) long. It is sparsely to densely covered with short, appressed, nonglandular hairs; with longer, spreading, nonglandular hairs; and sometimes with minute, gland-tipped hairs.

Each flower is 1″ to 1½″ (25 to 40 mm) wide. There are 4 outer floral leaves (sepals), 4 petals, 8 stamens, and 1 style. The sepals are green to yellowish green, ⅜″ to 11⁄16″ (9 to 18 mm) long, and strongly bent backward. The midribs are not keeled, and the pubescence is similar to the floral tube. The petals are yellow to pale yellow, ¼″ to ¾″ (7 to 20 mm) long, and 5⁄16″ to 13⁄16″ (8 to 21 mm) wide. They are very broadly inversely heart-shaped, but they are sometimes only slightly notched at the tip. They fade to orange or pale yellow as they begin to wither. The stamens have ¼″ to ⅝″ (7 to 15 mm) long filaments and ⅛″ to ⅜″ (4 to 10 mm) long anthers. The style has a distinctive, 4-lobed, cross-shaped stigma that is surrounded by the anthers when the flower is fully expanded (anthesis). The flowers open around sunset and close by noon except on cloudy days, when they remain open. They change from closed to fully open in just one minute. They are pollinated by hawk moths or sphinx moths, which feed on their nectar at night. The hypanthium, petals, and sepals are deciduous, withering and falling off when the fruit is formed.

The fruit is a ¾″ to 1¾″ (20 to 43 mm) long, ⅛″to ¼″ (4 to 7 mm) wide, four-celled, seed capsule. It is elongated, cylindrical, straight, widest below the middle, and tapered slightly toward the tip. It is dull green or grayish green, and it does not blacken when dry. It is moderately hairy. Each capsule cell contains two rows of dark brown to nearly black seeds. The seeds are prismatic, exhibiting multiple distinct flat surfaces.

20″ to 80″ (50 to 200 cm)

Yellow to pale yellow

Prairie hillsides, forest openings, open woodlands, lake shores, stream sides, abandoned fields, roadsides, railroads, and ditches. Moist soil.

July to August

Sources

3, 4, 28, 29, 30.

Native

Common

The family name refers to the flowers which are partially to fully closed during the day, open in the evening, and close at noon. The plants are pollinated by hawk moths and sphinx moths, which feed on their nectar at night.

Alfredo Colon
8/3/2022

Location: Albany, NY