Silene spaldingii

Distinct species.

Silene spaldingii is a perennial forb occurring in grasslands, sagebrush-steppe communities, and occasionally in open pine forests of western North America. It is a regional endemic of eastern Washington, northeastern Oregon, northern Idaho, and western Montana in the United States, extending into southern British Columbia, Canada. There are an estimated 132-139 occurrences of this species containing approximately 110,000 individuals. However, threats to Silene spaldingii are significant and include habitat degradation due to invasive plants, development, cattle grazing, alteration of fire regimes, predation, herbicide drift, and climate change. Range-wide, a significant amount of habitat has been lost to conversion to agriculture, restricting most remaining occurrences to small, isolated fragments of native vegetation, where they are vulnerable to degradation. To date, conservation activities for Silene spaldingii have included an impressive array of research, monitoring, invasive plant control efforts, outplanting activities, prescribed burns, and partnerships to protect core habitat. As of 2020, 23 Key Conservation Areas (KCAs) spanning various jurisdictions have been established across this species' range to protect, manage, and monitor this rare plant.

Silene spaldingii occurs in western North America as a regional endemic of eastern Washington, northeastern Oregon, northern Idaho, western Montana in the United States, and extending into southern British Columbia, Canada (USFWS 2007). In the United States it occurs in five physiographical regions: the Poulouse Prairie grasslands of Idaho and Washington, the Channeled Scablands of eastern Washington, the Blue Mountain Basins in Oregon, the Canyon Grasslands of the Snake River and its tributaries, and the Intermontane Valleys of Montana. Range extent was estimated using herbarium specimens and NatureServe Network occurrence data collected between 1994 and 2025 (RARECAT 2024, NatureServe 2025, SEINet 2025).

By applying a 1.6 km separation distance to herbarium records and NatureServe Network occurrence data documented between 1994 and 2025, there are estimated to be 132 occurrences rangewide (RARECAT 2024, NatureServe 2025, SEINet 2025). This separation distance is typically used for this species to delineate populations in Idaho and Washington (USFWS 2020). However, Montana and Oregon use a finer-scale separation distance of less than 1.6 km. The U.S. Fish and Wildlife Service estimated that there were 139 occurrences in the United States in the most recent Five Year Review for the species conducted in 2020.

Threats to Silene spaldingii are summarized below (Hill and Gray 2004):

"Threats of greatest concern to the continued existence of S. spaldingii include, in order of priority: 1) habitat degradation from weed invasion and livestock grazing, 2) habitat loss and fragmentation and associated genetic pressures of small populations, i.e., pollinator limitation, inbreeding depression, loss of populations, 3) alteration of fire regimes, including fire suppression, increasing fire frequencies, and out-of-season fires, 4) predation by herbivores, including domestic livestock, native ungulates, rodents and insects, 5) herbicide drift, and 6) prolonged drought and global warming."

Many remaining occurrences are in small remnant, isolated fragments of native vegetation, and 50 occurrences are found entirely on privately owned (or partially privately-owned) lands (USFWS 2007). These populations are vulnerable to changes to land-use practices such as livestock grazing and trampling and development. Hill and Gray (2004) considers habitat loss due to urban, agriculture, and recreational development to be an ongoing and significant threat to this species.

Populations are also threatened by agricultural practices, including the application of herbicides and grazing (USFWS 2007). Livestock grazing, in particular, is a significant threat to Silene spaldingii, both directly—by removing seedheads and flowers, thereby limiting reproduction—and indirectly, through trampling, which can damage seedlings or roots. Heavy grazing pressure by cattle has also degraded fescue bunchgrass communities and promoted the establishment of invasive species through selective grazing and disturbance (Hill and Gray 2004).

Most populations are threatened by invasive annual grasses such as Bromus japonicus (Japanese brome), Bromus secalinus, Bromus tectorum (cheatgrass), and Ventenata dubia, which alter fire regimes, degrade rangelands, and compete with native plant vegetation where S. spaldingii occurs (USFWS 2007). Invasive rhizomatous plants such as Acroptilon repens (Russian knapweed), Chondrilla juncea (rush skeletonweed), and invasive Cirsium spp. also co-occur with Silene spaldingii and can invade and outcompete native plant communities. Centurea solstitialis in particular is found in the vicinity of all known occurrences in Idaho and is an aggressive invasive plant known to form monocultures.

The alteration of natural fire regimes through fire suppression has led to increasing fire severity and frequency throughout the range of S. spaldingii and has led to community successional changes such as the invasion of sagebrush steppe habitat by deciduous shrubs and ponderosa pine in Washington. Increasing fire frequencies and severity due to invasive annual grasses, and out-of-season fires occurring in fall, winter, and spring when the species is actively growing are additional concerns.

Predation of S. spaldingii by deer, elk, rodents, and insects has been documented at populations throughout the range of the species. A 2012 demographic study found that over 75% of plants that emerged were impacted by insect predation and/or ungulate browse, and few plants produced seed (Taylor et al. 2012).

Herbicide drift due to invasive plant control by landowners and land managers is a threat to plants, particularly for populations occurring on private lands, State lands, and along highway rights-of-ways (USFWS 2007). Shifting climate and increased prevalence and severity of drought due to climate change is a concern for this species, though its specific effects are unknown.