Phacelia formosula

Phacelia formosula was first discovered by George Osterhout in Jackson County, Colorado in 1918 and was published as a species in 1919 (Osterhout 1919). More recently, two morphologically similar populations of Phacelia were discovered in Larimer and Grand counties, Colorado (P. "scullyi" [not published] and P. gina-glenneae, respectively) (Atwood and Welsh 2013, Neale et al. 2014). Since their discoveries in 2004 and 2010 genetic and morphologic research of the Phacelia populations has been on-going. Initial results indicated that there was no distinction between the Jackson and Larimer county populations (Riser et al. 2020), and that the Grand County population of P. gina-glenneae (Atwood and Welsh 2013) was a separate entity. However, additional studies conclude that taxonomic separation of the three Phacelia groups in Larimer, Jackson, and Grand counties is not warranted and that P. gina-glenneae and P. scullyi should be subsumed into Phacelia formosula (Naibauer and McGlaughlin 2022). We consider the concept of P. formosula to include the Larimer and Jackson populations and maintain the concept of P. gina-glenneae until recent research has been published (CNHP 2022).

Phacelia formosula is a small, annual or biennial plant species that is endemic to North Park and the Laramie River Valley in Jackson and Larimer counties of Colorado, USA. There are 10 extant occurrences (11 if the species concept includes P. gina-glenneae). Phacelia formosula's growth habit leads to extreme annual fluctuations in population size, this combined with genetic isolation of the populations makes the species highly vulnerable to stochastic events. The species and its habitat are threatened by livestock grazing, competition from invasive plant species, recreation use, oil and gas development, drought and habitat shifting and alteration associated with climate change.

Phacelia formosula is endemic to Jackson and Larimer counties in north central Colorado (USA); it is found on the Coalmont Formation in Jackson County and the Niobrara Formation in Larimer County. The estimated range extent in Colorado of 721 square kilometers was calculated in GeoCAT using occurrence data provided by the Colorado Natural Heritage Program (2026). When the species concept includes P. gina-glenneae the range is 1854 square kilometers and extends south into Grand County (CNHP 2026).

As of 2026 there are 12 known locations documented in the Colorado Natural Heritage Program database, and one additional occurrence that is the site for the species concept Phacelia gina-glenneae. Of the 12 known locations, two of the occurrences have not been observed in over 20 years, therefore 10 occurrences are currently considered to be extant.

Threats to Phacelia formosula include motorized recreation, inappropriate livestock grazing, competition from invasive plant species, and road and powerline maintenance. Off highway vehicle use has been reported from 45% (5 of 11) extant occurrences (CNHP 2022). Invasive species, primarily Salsola (Russian thistle) are also reported from 45% of the extant occurrences, an increase of 18% since 2019 (CNHP 2022). Livestock grazing is reported as the predominant land use within 81% of the occurrences, and cattle trailing and trampling have been observed within several occurrences (CNHP 2022). Two occurrences have a powerline passing through P. formosula habitat, and just over 50% of the occurrences are along or near roads where fugitive dust and road maintenance activities may impact the species. This species is considered to have low adaptive capacity and is expected to be extremely vulnerable to climate change under both RCP 4.5 and 8.5 scenarios, as assessed for the 2025 Colorado State Wildlife Action Plan (CNHP 2025).