Oenothera rhombipetala

Herbs biennial, densely to sparsely strigillose, sometimes also sparsely glandular puberulent distally. Stems sometimes with lateral branches arising obliquely from rosette, 30–100(–150) cm. Leaves in a basal rosette and cauline, basal 6–20 × 0.6–2 cm, cauline 3–15 × 0.8–2.5 cm; blade narrowly oblanceolate, gradually narrowly elliptic to narrowly lanceolate, oblanceolate, or ovate distally, margins lobed to remotely dentate or subentire; bracts slightly longer than capsule they subtend. Inflorescences dense, usually without lateral branches, mature buds usually not overtopping spike apex. Flowers 2–several per spike opening per day near sunset; buds erect, with free tips erect, 0.5–3 mm; floral tube slightly curved upward to ± straight, 30–45 mm; sepals 15–30 mm; petals yellow, broadly elliptic to rhombic-elliptic, 15–35 mm; filaments 13–25 mm, anthers 3–8 mm, pollen 85–100% fertile; style 25–50 mm, stigma exserted beyond anthers at anthesis. Capsules narrowly lanceoloid, 13–25 × 2.5–3 mm. Seeds brown, sometimes flecked with dark red spots, ellipsoid, 1–1.7 × 0.4–0.7 mm. 2n = 14.

Phenology: Flowering May–Oct.
Habitat: Fields, prairies, sandy soil.
Elevation: 60–600(–1300) m.

Ark., Colo., Ill., Kans., Mich., Minn., Mo., Nebr., N.Mex., Okla., S.Dak., Tex., Wis.

Discussion

Oenothera rhombipetala is primarily a central plains species that has scattered localities in the Midwest to Illinois, Michigan, and Wisconsin, and barely entering the easternmost parts of Colorado and New Mexico.

Oenothera rhombipetala had a broader delimitation (P. A. Munz 1965) until W. Dietrich and W. L. Wagner (1988) divided it into three species (O. clelandii, O. curtissii, and O. rhombipetala), with both of the split-off species being PTH. Evidence gathered by Dietrich and Wagner showed that these PTH species are geographically separated populations of small-flowered plants, and although they are very close morphologically, their distributions and morphological differences suggest that they were each derived independently from O. rhombipetala. Oenothera rhombipetala is self-incompatible.

Oenothera pyramidalis H. Léveillé is a superfluous name and pertains here.

Selected References

None.

Lower Taxa