Flora of North America species comparison

Subspecies trichocalyx occurs across central to southern Wyoming, eastern Utah, western Colorado, northeastern Arizona, and northwestern New Mexico. Within its range it has slight overlap with subspp. pallida and runcinata. In its purest form, subsp. trichocalyx is the most distinctive phase of Oenothera pallida, but many of the populations have characteristics that approach other subspecies with perennial habit (versus annual) appearing occasionally. Plants that are glabrous, or nearly so, like subsp. pallida, but with apparent short-duration habit and divided leaves like subsp. trichocalyx, occur in southern Wyoming and in the Uinta Basin region of Utah; only more typical plants of subsp. trichocalyx otherwise occur in the region without any current evidence of the presence of subsp. pallida.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The distribution of subsp. pallida centers in the intermountain region from Oregon and Washington east of the mountains, adjacent southern British Columbia, south through southern Idaho, Wyoming, western half of Utah, southern Nevada, to northern Arizona, northwestern New Mexico, and adjacent southwestern Colorado. There are morphological intermediates with subspp. runcinata and trichocalyx. Densely strigillose plants occur within the range of subsp. pallida, especially near the St. Anthony Dunes in Idaho, and have been referred to as var. idahoensis.

Baumannia douglasiana Spach is an illegitimate name that pertains here.

(Discussion copyrighted by Flora of North America; reprinted with permission.)