Cutleaf Evening Primrose
Oenothera laciniata is a non-native annual herb with long, slender, dentate (toothed) leaves and white flowers. The common name comes from the fact that flowers usually open just before sunset. It is now mostly found in camp and West Turnaround RA.
Figure 78: Oenothera laciniata
Oenothera cotyledons are cuneate (wedge-shaped) and broadly rounded at both the tip and base. They share this basic shape with Anagallis, which differs in being sessile (lacking a stem) so that the two cotyledons butt up against each other. The first true leaves are generally elliptic (oval, rounded at both ends) and sometimes tightly clustered. Close examination reveals coarse bristles on the leaves.
As the plant grows the central nerve becomes prominent and the leaves are oblanceolate (lance-shaped but wider towards the end). These basal leaves differ somewhat from the cauline leaves (leaves growing from a stem), which are described as obovate (oval, wider at the ends) to narrowly elliptic. We rarely see Oenothera reach this stage and they are presumably easy to identify based on the flowers.
Though somewhat similar in form, Oenothera (left) is easily distinguished from Lepidium (middle), and Sonchus (right) based on color and leaf dentition. The teeth on Oenothera leaves are larger, broader, and more rounded than either Lepidium or Sonchus.
Description: Taprooted annual herbs; stems erect to procumbent, 0.5-5 dm long, usually branched, strigillose, sparsely villous, and usually glandular-pubescent in the inflorescence. Basal leaves oblanceolate, 5-13 cm long, 1-3 cm wide, margins lobed or dentate; cauline leaves narrowly obovate to narrowly elliptic, 2-10 cm long, 0.4-3.5 cm wide, lobed, dentate, or occasionally subentire. Flowers solitary in the leaf axils, usually only 1 opening each day per stem near sunset; floral tube 1.5-3.5 cm long; sepals with distinct tips 1-3 mm long; petals pale yellow or yellow, broadly obcordate, 0.5-1.3 (-2) cm long; pollen ca. 50% fertile; stigma surrounded by anthers at anthesis. Capsules 2.5-5 cm long. Seeds in 2 rows per cell, ellipsoid to subglobose, 0.8-1.8 mm long, the surface pitted. Self-compatible, autogamous, permanent translocation heterozygote (Wagner et al., 1999; p. 1000).