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Oenothera hartwegii  Benth.
[=Calylophus hartwegii  (Benth. ) Raven]
Barber County, Kansas
Height: 2-16 inches
Family: Onagraceae - Evening Primrose Family
Flowering Period:   April, May, June, July
Also Called: Hartweg's sundrops, fendler evening primrose.
Stems: Decumbent or slightly ascending, 1 to several, usually branched, nearly glabrous throughout.
Leaves: Alternate, simple, somewhat ascending, linear to oblanceolate or lanceolate, up to 2 inches long, less than 1/2 inch wide, glabrous; margins entire or serrate; tips pointed; stalks mostly absent; stem leaves sometimes have clusters of small leaves in axils.
Inflorescences: Flowers in axils of upper leaves.
Flowers: Sepals 4, each without keeled midrib, pale yellow, sometimes fade pinkish or orange; floral tube .5 to 2.5 inches long, lower half tubular ; petals 4, yellow, fading pinkish or purplish; stamens 8, nearly equal; style mostly longer than stamens; stigma flat, 4-sided, shield-shaped.
Fruits: Capsule, cylindrical, .2 to 1.6 inch long, sessile; seeds less than 1/10 inch long.
Habitat: Prairie hillsides, valleys, roadsides, and open woods; rocky or gravelly soils.
Distribution: Southern portion of the southwest 1/4 of Kansas.
Uses: The plant was used by the Navajo to treat internal bleeding.
Comments: The flowers open in the late afternoon or near sunset. The related subspecies Calylophus hartwegii (Benth.) Raven ssp. pubescens (A. Gray) Towner & Raven is also found in the same area. It is usually covered with long spreading hairs.

Hartweg evening primrose flower
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