Polypodium saximontanum

Sigel et al. (2014) and Assis et al. (2016) confirm the monophyly and circumscribe the genus Polypodium. The generic placement of this taxon is in accordance with the Pteridophyte Phylogeny Group I (2016).

Polypodium saximontanum is a perennial fern occurring on cracks and ledges of granitic or gneissic rocks of the mountains of northern New Mexico, Colorado, eastern Wyoming, and extreme western South Dakota. It was also documented in western Montana in 2011. There are an estimated 53 occurrences of this species rangewide, which are threatened by the loss of overstory tree canopy cover as a result of logging or other factors such as bark beetle infestations, recreational activities, climate change, and collection from the wild for medicinal use. The remote and relatively inaccessible nature of its habitat on cliff faces is thought to naturally protect Polypodium saximontanum from most direct anthropogenic threats.

Polypodium saximontanum occurs in the western United States, in mountain regions of north-central New Mexico, Colorado, eastern Wyoming, in the Black Hills region of western South Dakota, and, as of 2011, in western Montana (FNA 1993, Wyoming Natural Heritage Program 2012, Sigel et al. 2014, Heil and O'Kane 2025). In Wyoming, this species occurs in Albany, Carbon, and Converse counties in the southern Laramie Range and Platte River Canyon in the Medicine Bow Range (Wyoming Natural Heritage Program 2012). In Colorado, this species occurs in seventeen counties (Archuleta, Boulder, Clear Creek, Douglas, El Paso, Grand, Gunnison, Hinsdale, Huerfano, Jefferson, Larimer, Logan, Ouray, Pitkin, Pueblo, Routt, and Saguache) (CNHP 2024). In 2011, Polypodium saximontanum was also collected from the mountains of western Montana in the Bitterroot National Forest of Ravalli County, which expanded the known range of this species by approximately 800 kilometers to the northwest (Sigel et al. 2014). Range extent was estimated using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1994 and 2025 (GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2025, SEINet 2025).

By applying a 1 km separation distance to herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, it is estimated that there are 53 occurrences rangewide (GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2025, SEINet 2025). The Colorado Natural Heritage Program estimates that there are 20-30 occurrences in the state based on records tracked in their internal database and herbarium specimens (CNHP 2024). The Wyoming Natural Heritage Program estimates that there are five extant occurrences in the state, all of which have been surveyed since 1986 (Wyoming Natural Heritage Program 2012).

Prior to its recognition as a unique species, collections were variously referred to as P. montense, P. amorphum, P. hesperium and P. virginianum (FNA 1993). Polypodium saximontanum is morphologically distinguishable from all these species and also has a different range from both P. amorphum and P. virginianum. However, these early misidentifications may have caused some confusion, and there may be misidentified specimens still occurring in herbaria. For example, the collection from Montana (Erin M. Sigel 2011-41a (DUKE, MONTU)) was initially identified as Polypodium hersperium, which is a morphologically similar species and the only Polypodium included in the Manual of Montana Vascular Plants (Lesica 2012, Sigel et al. 2014).

Threats to Polypodium saximontanum across its range are not well documented but include the loss of overstory tree canopy cover as a result of logging or other factors such as bark beetle infestations, recreational activities (especially rock climbing), and changes to the hydrological regimes as a result of climate change (NatureServe 2025, CNHP 2024). In addition, Polypodium species are recommended in popular medicinal plant guides (e.g. Forey and Lindsay 1991). This may threaten populations near urban centers, but the remoteness of many of the areas where it grows suggests that it is unlikely that this is a significant threat. Similarly, the habitat inhabited by this species on cliff faces and cervices are unlikely to be impacted by typical human land uses in the near future (Wyoming Natural Heritage Program 2012, CNHP 2024).