Missouri Evening Primrose
Oenothera macrocarpa
Evening Primrose family (Onagraceae)

Description: This herbaceous perennial plant is up to 1' tall, and unbranched or sparingly so. The short stems are more or less erect. The alternate leaves are up to 6" long and 1" across; they are rather densely crowded along the stems. Their margins are smooth, or slightly dentate with widely spaced teeth; they often curve upward. The leaves are narrowly lanceolate or oblanceolate, with white veins; the upper surface of young leaves is often shiny. Lower leaves have petioles up to 1" long, while upper leaves are often sessile.

The large flowers develop singly from the upper axils of the leaves. Each flower has a winged capsule containing the ovaries that is 1–2" long; it is located adjacent to the leaf axil. A calyx tube from 2-6" connects the capsule to the rest of the flower. At the apex of the calyx tube, the flower has 4 yellow petals; it spans about 5" across. These petals are subtended by a division of the calyx into lanceolate tips that curve downward; these are purple-spotted. At the throat of the flower, are 8 stamens with linear anthers, and a long style with a stigma that is cleft into a cross-like shape. These reproductive parts are yellow. The flower buds are about 1-4" long, depending on their maturity, and quite conspicuous. They are purple-spotted and orbicular, tapering at both ends. The flowers open during the evening and close the following morning, each one lasting a single day. The blooming period occurs from early to mid-summer, and lasts about 2 months. There is a mild floral fragrance. The seeds are irregularly shaped and crested. The root system consists of a deep taproot. This plant reproduces by reseeding itself.

Cultivation: The preference is full sun, dry conditions, and lean soil that is either rocky or sandy. Most growth occurs during the first half of the year, afterwhich it forms seeds and becomes dormant (although it doesn't necessarily die down). This plant will grow in more fertile soil if it is well-drained, but has difficulty competing with taller plants.

Range & Habitat: In Illinois, the native Missouri Evening Primrose has been observed in natural habitat in only St. Clair county, where it may be extirpated (see Distribution Map). Habitats include hill prairies and limestone glades. Outside of the state, this plant is also observed in dry prairies and barrens with sparse vegetation; these habitats often have gravelly or sandy soil. Missouri Evening Primrose is often grown in flower gardens.

Faunal Associations: Sphinx moths pollinate the flowers while seeking nectar. Various bees may visit the flowers to collect pollen during the early morning or evening, but they are too small to be effective pollinators. Little information is available about this plant's relationships to birds or mammals.

Photographic Location: The photographs were taken at Crystal Lake Park in Urbana, Illinois.

Comments: Missouri Evening Primrose has striking flowers that are quite large for the size of the plant. It can be confused with no other plant that occurs (or used to occur) in the natural habitats of Illinois.