Oenothera clelandii

Native

Dry soils. Prairies, fields, roadsides, and waste places. Full sun. Sandy soil.

June to October

Yellow

16″ to 40″

This is a 16″ to 40″ tall, erect, biennial forb that rises from a taproot.

In the first year it forms a 3″ to 6″ wide rosette of basal leaves. In the second year it sends up a flowering stem. It usually dies after bearing fruit once.

The stems are erect or ascending, seldom branched, light green, and densely covered with white, appressed hairs.

The leaves are alternate, ascending to widely spreading, linear to narrowly lance-shaped or linear-oblong, 1¾″ to 3⅛″ long, and ¼″ to ¾″ wide. The upper surface is medium green and sparsely covered with short, white, appressed hairs. The lower surface is paler green and densely covered with short, white, appressed hairs. The margins are mostly untoothed, though sometimes there are barely perceptible teeth near the tip.

The inflorescence is a dense, 4″ to 12″ long spike of numerous flowers at the end of the stem and branches. The central axis of the stalk (rachis) is densely covered with short, white, appressed 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 and covered with straight, stiff, sharp, appressed hairs. When in bud it is ⅝″ to 13 ⁄16″ long, 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 ½″ to 1¼″ in diameter when fully open. There are 4 green sepals and 4 yellow petals. The sepals are linear, 3 ⁄16″ to ⅝″ long, and strongly bent backward along the flower stalk. The petals are yellow, broadly elliptic or egg-shaped, 3 ⁄16″ to ⅝″ long, and usually pointed at the tip. There are 8 equal stamens, 4 united styles, and a distinctive, 4-lobed, cross-shaped stigma. The flowers open around sunset and on cloudy days, and close by noon. 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 cylinder-shaped, ⅜″ to 11 ⁄16″, 4-celled capsule. The capsule is round in cross section, 4-sided with rounded angles, curved near the base, and densely covered with white, appressed hairs. Each cell of the capsule contains two rows of dark brown, egg-shaped seeds.

Fourpoint evening primrose (Oenothera rhombipetala) flower sepals are much larger, ⅝″ to 1″ long. The flower petals are much larger, ⅝″ to 1″ long.