common evening primrose

not listed

N5 - Secure

SNR - Unranked

not listed

FACU - Facultative upland

FACU - Facultative upland

FACU - Facultative upland

Common evening primrose is an erect, biennial forb that rises usually on a single stem from a fleshy taproot. It can be up to 80″ tall, though it is usually much shorter. In the first year it forms a rosette of basal leaves. In the second year it sends up a flowering stem. It dies after bearing fruit once.

The rosette leaves are green to pale green, stalked, narrowly inversely lance-shaped or lance-shaped, 4″ to 12″ long, and ¾″ to 2″ wide. The blade is broadly or narrowly angled at the tip and tapers gradually to the leaf stalk at the base. The upper and lower surfaces are covered with minute, straight, sharp, stiff, appressed hairs. The margin is toothed. The teeth are sometimes blunt, sometimes widely spaced. The lower part of the blade sometimes has broad, wavy teeth or is lobed.

The stem is erect, green, leafy, and sometimes flushed with red near the base. It may be unbranched or have a few branches rising from the rosette or a few branches on the main stem. It is densely to sparsely covered with minute, straight, sharp, stiff, appressed hairs, and also with longer, somewhat appressed to spreading hairs.

Stem leaves are alternate, narrowly inversely lance-shaped to lance-shaped or narrowly elliptic to elliptic, 2″ to 8½″ long, and ⅝″ to 2″ wide. The blade is narrowly angled at the tip and wedge-shaped or tapered at the base. They are otherwise similar to rosette leaves. There is often a cluster of smaller, secondary leaves in the axil of the leaf.

The inflorescence is a stiff, relatively open spike of numerous flowers at the end of the stem and branches. The spike is unbranched but there is often a secondary spike below the main one. The central axis of the spike (rachis) sometimes red. It is densely to sparsely covered with minute, straight, sharp, stiff, appressed hairs, and also with longer, somewhat appressed to spreading hairs.

The individual flowers are stalkless. What appears to be a flower stalk is actually a structure formed by the fused bases of the sepals, petals, and stamens (hypanthium). The hypanthium is yellowish-green, sometimes flushed with red. It is sparsely to densely covered with short, straight, glandular hairs and also sparsely covered with long, soft, shaggy hairs. When in bud it is 1″ to 19 ⁄16″ long, 1 ⁄32″to 1⁄16″ in diameter, widely spreading near the rachis then strongly ascending, with the bud held upright. When in bloom the hypanthium elongates, straightens somewhat, and the flower is held at about a 45° angle.

The flowers are crowded and 1″ to 2″ in diameter when fully open. There are 4 sepals, 4 petals, 8 stamens, and 1 style. The sepals are yellowish-green, linear, ½″ to ⅞″ long, and strongly bent backward along the hypanthium. The petals are yellow, rarely pale yellow, very broadly egg-shaped, ½″ to 1″ long, and 9 ⁄16″ to 11 ⁄16″ wide. They are broadly rounded and notched at the tip. They fade to orange as they begin to wither. The stamens extend only slightly beyond the corolla. They have 5 ⁄16″ to ⅝″ long filaments and ⅛″ to ¼″ long anthers. The style has a distinctive, 4-lobed, cross-shaped stigma. The flowers open around sunset and on cloudy days, 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 flowers have a mild lemony scent.

The fruit is a cylinder-shaped, ¾″ to 19 ⁄16″ long, ⅛″ to ¼″ in diameter, 4-celled capsule. The capsule is green, stalkless; bluntly 4-angled with rounded angles; thickest at the base and tapered toward the tip; and straight, not curved near the base. Each cell of the capsule contains two rows of dark brown, egg-shaped seeds. The seeds do not have a tuft of hairs (pappus) at the top.

20″ to 80″

Yellow

Cleland’s evening primrose (Oenothera clelandii) is a smaller plant, no more than 40″ in height. The flowers are smaller and have diamond-shaped petals. The seed capsules are smaller and are curved.

Cut-leaved evening primrose (Oenothera laciniata) is a short plant, reaching only 18" at maturity. The leaves are lobed.

Northern evening primrose (Oenothera parviflora) has smaller flowers, no more than one inch wide.

Nuttall’s evening primrose (Oenothera nuttallii) has white flowers.

Perennial evening primrose (Oenothera perennis) is a shorter plant, reaching only 24″ at maturity. It has smaller flowers, ⅓″ to ¾″ wide.

Rhombic evening primrose (Oenothera rhombipetala) flower has diamond-shaped petals.

Toothed evening primrose (Oenothera serrulata) is a much shorter plant, reaching only 24″ at maturity. It is usually found with clustered stems, which may be woody at the base. The leaves are toothed, and are linear or oblong and narrow.

Dry to moderate moisture. Prairies, fields, thickets, roadsides, railroads, disturbed sites and waste places. Full sun.

June to October

Sources

2, 3, 4, 5, 7, 28, 29, 30.

Native

Common and widespread

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.

Plant

Inflorescence

Flower

Infructescence

Winter