Virginia Tech Weed Identification Guide

Common Eveningprimrose: Oenothera biennis

oenothera1-15b.jpg (97613 bytes) Weed Description:  Usually a biennial or a winter annual, but may rarely occur as a summer annual.  Common eveningprimrose has narrow leaves with untoothed margins and produces many showy yellow flowers.  This weed is primarily a weed of landscapes, nurseries, some agronomic crops, and occasionally turfgrass and lawns.  Common eveningprimrose occurs throughout the southern and eastern United States.
Seedlings:  Cotyledons are 6 to 11 mm long, and usually egg-shaped with a short petiole.  The stem at the base of the cotyledons has a reddish tint.  Leaves initially develop as a basal rosette.   Upper leaf surfaces of young leaves may have a few hairs near the base. oenothera1-15.jpg (138727 bytes)
oenothera3-30.jpg (206782 bytes) Leaves:  Leaves are elliptic to lanceolate in outline, are relatively narrow, and have untoothed margins.  Leaves have a distinctive white or pink midvein and may have wavy margins.  Leaves along the erect flowering stem are alternate and become progressively smaller up the stem.
 

Stems:  Erect, reaching as much as  6 1/2 feet in height.

Roots:  A taproot.

oenothera4-6b.jpg (74287 bytes)
cevngprmrose5-15c.jpg (72813 bytes) Flowers:  Occur in the upper leaf axils and are without flower stems (sessile).  Flowers consist of 4 bright yellow petals (12 to 25 mm long).    Individual flowers are approximately 3/4 to 2 inches wide.

Fruit:  An erect, hairy capsule that is approximately 1/2 to 1 1/2 inches long.  Many seed are arranged in rows within the capsule.

Identifying Characteristics:  Erect plants with lanceolate or elliptic leaves that have untoothed margins, and showy yellow flowers.   Common eveningprimrose is very similar in appearance to Cutleaf Eveningprimrose (Oenothera laciniata), but cutleaf eveningprimrose has toothed margins and usually grows much more prostrate than common eveningprimrose.