Oenothera macrocarpa

This herbaceous perennial produces a red stem up to 46 cm (18 in) in height.[6] The plant can sprawl along the ground up to 0.6 m (2 ft).[4] Leaves are long and narrow, about 15 cm (6 in) long by 3 cm (1 in) across, and are densely crowded in an alternate arrangement along the stem.[6] They have either smooth margins or broadly spaced teeth and are hairy.[7]

The large flowers, up to 13 cm (5 in) across, are cup shaped with four petals, canary yellow, and have a mild fragrance. They are produced in great numbers from early to mid summer. The flowers last for one day, opening in the evening and closing the following morning.[6] The seed pods are 4-winged and 52–75 mm (2–3 in) long.[7]

There are five commonly accepted varieties.[8] These are:

• O. macrocarpa var. fremontii - restricted to Kansas and southern Nebraska[9]
• O. macrocarpa var. incana - southern Kansas, western Oklahoma and northern Texas
• O. macrocarpa var. macrocarpa - the most widespread; Texas to the Ozark Mountains, with disjunct populations in Tennessee's Nashville Basin[10]
• O. macrocarpa var. mexicana - known only from Coahuila, Mexico[11]
• O. macrocarpa var. oklahomensis - southern Kansas, Oklahoma and northern Texas

• 
  O. m. subsp. macrocarpa
• 
  O. m. subsp. incana
• 
  O. m. subsp. fremontii
• 
  Fruit

The genus name Oenothera is from the Greek for "wine-scented". The specific epithet macrocarpa is also from the Greek, meaning "large fruited".[12]

Oenothera macrocarpa is native to Arkansas, Illinois, Kansas, Missouri, Nebraska, Oklahoma, Tennessee, Texas, and northeast Mexico.[13] Habitats include limestone outcrops, glades, bluffs, rocky prairies, quarries, and roadsides.[7]

The flowers are pollinated by night-flying moths, such as sphinx moths (Sphingidae).[6]

The seed pods are often used in flower arrangements. This plant is also grown in gardens for its flowers.[14][15] It is suitable as a groundcover in poor, stony soil which does not become waterlogged in winter, in full sun. It has gained the Royal Horticultural Society’s Award of Garden Merit.[2][16]