Oenothera acutissima (Onagraceae), a New Species from Northwestern Colorado and Adjacent Utah

Abstract

Oenothera acutissima W. L. Wagner is a rare new species of sect. Lavauxia from Moffat Co., Colorado, and adjacent Daggett Co., Utah. Oenothera acutissima is clearly distinguished from its closest morphological relatives, 0. flava and 0. triloba, by its long slender branching taproot, which is capable of vegetative reproduction by producing new shoots along its length, linear irregularly dentate leaves, deep reddish-orange color of the faded petals, and small, fewer-seeded cap- sules. It occurs in seasonally moist sandy soils in medium altitude conifer forests to sagebrush scrub communities, whereas O.fiava grows in heavier clay soils and rarely comes in contact with 0. acutissima. Attempts to produce artificial hybrids produced mostly empty seed, but with difficulty two variegated plants were obtained. The distinctive new species of Oenothera described here was first rec- ognized by William M. Klein, who collected it with the late H. D. Har- rington at Stuntz Reservoir, Moffat County, Colorado, in 1966. A decade later, I initiated the preparation of a revision of Oenothera L. sect. La- vauxia (Spach) Endl. and was able to confirm Klein's suggestion that this population did represent an undescribed species. It is now known from a few scattered localities in Moffat Co., Colorado, and adjacent Daggett Co., Utah. In 1978, I studied a population consisting of approximately 15 scat- tered individuals of this species in the Douglas Mountain area of Colo- rado. At the same time, Elizabeth Neese and Scott Peterson located a population at Flaming Gorge, Daggett Co., Utah, from which Peterson kindly provided seed for the cultivation of a second strain for further study. I am publishing the name of this species in advance of my revision of the section primarily because of the current listing of the species in the Federal Register by U.S. Fish and Wildlife Service (1980, p. 82524) as Oenothera sp., a potentially threatened species.