Pediocactus winkleri

Analysis of DNA sequences provide evidence of a close relationship among P. winkleri, P. despainii, and P. simpsonii (FNA 2003b). The morphological distinction between P. winkleri and P. despainii is much more tenuous than the key and descriptions indicate.

Pediocactus winkleri is a small cactus that is endemic to silty-loam and clay soils derived from Morrison and Dakota formations in salt brush communities of south-central Utah, USA. The species is known from just sixteen widely scattered occurrences located primarily in Capitol Reef National Park and on Bureau of Land Management lands. It is seriously threatened by heavy grazing by cattle and wildlife, and drought, as well as disturbances from recreational use, off-road vehicle use, and possible coal and oil exploration. Additional threats include illegal take by cactus collectors and predation by insects and mammals.

Pediocactus winkleri occurs in western North America, where it is endemic to south-central Utah in Emery, Sevier, and Wayne counties in the United States (USFWS 2019). This cactus occurs in small populations widely scattered over a small area from the far northwest corner of Captiol Reef National Park in Sevier County to just south of Notom in central Wayne County. A disjunct population also exists near Hanksville in Wayne County. The range of P. winkleri overlaps in its northern extent with populations of the listed cactus P. despainii, and the northern boundary of Capitol Reef National Park is used by all land management agencies as an artificial boundary between these two species, even though some of the boundary populations may include hybrids or plants with P. despainii genetics (USFWS 2016). Range extent was calculated at 1285 sq km using data from the Utah Rare Plant Database (2021, UNHP 2021).

By applying a 2 km separation distance to population location data from the Utah Rare Plant Database (2021), there are sixteen estimated occurrences (UNHP 2021).

Livestock grazing was identified as a significant threat to this species in the 2016 recovery plan (USFWS 2016), and trampling and disturbance by livestock increased cactus mortality and reduced probability of flowering in long term monitoring plots (Clark et al. 2015). Since 2016, Capitol Reef National Park removed grazing from an allotment that contained 94 percent of the individuals within the park (USFWS 2019). Drought also increased mortality and decreased recruitment for Winkler cactus in long-term monitoring plots (Clark et al. 2015), and increased drought conditions resulting from climate change is a concern for this species. Predation by larvae of the cactus borer beetle and by native rodents has impacted individuals, but levels of recorded damage are low on a species scale (USFWS 2016). Off-highway vehicle use and other recreational use and road maintenance activities occurs in the range of this species and is a threat, as well as mineral exploration and oil and gas development. Illegal collection of Winkler cactus was a significant threat in the past, and it continues to be a threat to this species at levels unknown.