Oenothera coloradensis (Rydberg) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 211. 2007.

Wagner, Warren L., Krakos, Kyra N. & Hoch, Peter C., 2013, Taxonomic changes in Oenothera sections Gaura and Calylophus (Onagraceae), PhytoKeys 28, pp. 61-72 : 66-67

4. Oenothera coloradensis (Rydberg) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 211. 2007.

Basionym.

Gaura coloradensis Rydberg, Bull. Torrey Bot. Club 31: 572. 1904. Gaura neomexicana var. coloradensis (Rydberg) Munz, Bull. Torrey Bot. Club 65: 114. 1938. Gaura neomexicana coloradensis (Rydberg) P. H. Raven & Gregory, Mem. Torrey Bot. Club 23: 63. 1973 [ “1972”].

Type.

United States. Colorado: Larimer County, Ft. Collins, 5000 ft, 8 Jul 1895, J. M. Cowen s.n. (Holotype: NY-BC00232160!; Isotype: GH!).

Biennial from a stout, fleshy taproot, with several branches from the base, 50-80(-100) cm tall, strigillose proximally, becoming glandular puberulent and strigillose distally. Leaves: rosette leaves 4-18 × 1.5-4 cm; cauline leaves 5-13 × 1-4 cm, very narrowly elliptic, subglabrous or strigillose, margin subentire to repand-denticulate. Flowers 4-merous, opening at sunset; floral tube 8-12 mm; sepals 9.5-13 mm; petals 7-12 mm; staminal filaments 6.5-9 mm, anthers 2.5-4 mm, pollen 90-100% fertile; style 19-25 mm. Capsule indehiscent, 6-8.5 × 2-3 mm, nut-like, hard, woody, not reflexed, the body ellipsoid or ovoid, sharply 4-angled, with fairly deep furrows alternating with the angles for 2-3 mm from the apex, ribbed from base of furrow to base of the fruit. Seeds 1-4, 2-3 mm, yellowish to light brown. Gametic chromosome number: n = 7. Probably self-compatible.

Phenology and distribution.

Flowering in July and August.In early successional vegetation of the North and South Platte River watersheds on the high plains, sloping floodplains, and drainage base in heavy soils, from southern Laramie and Platte counties in Wyoming, northern Weld County, Colorado, formerly near Fort Collins, Larimer County, Colorado, and in western Kimbal County, Nebraska; 1530-1950 m.

The Colorado butterfly plant is currently known from fewer than two dozen populations and has been federally listed as a Threatened species in the U.S. ( USDI Fish and Wildlife Service 2000). The primary threats are agricultural use of habitat, herbicide spraying to control weed species, and livestock trampling and grazing (see Fertig 2000, Heidel and Handley 2011, NatureServe 2013). Recent study by Krakos (unpubl.) has determined this species to probably be self-compatible.