Pediocactus peeblesianus

Heil and Porter's treatment in FNA (2003) recognizes two subspecies of Pediocactus peeblesianus: ssp. fickeiseniae (=P. peeblesianus var. fickeisenii) and the typical subspecies. Baker and Cloud-Hughes (2022) find "no practical manner in which to segregate groups of populations within Pediocactus peeblesianus to form any natural taxonomic boundaries. There is a weak morphological cline from the west to the east, in which central spines increase in number and length, and radial spines decrease in thickness. Populations of typical P. peeblesianus were based on neotenous individuals that probably occurred on very shallow soils, while those of P. peeblesianus var. fickeisenii occurred on deeper soils farther west along the east-west cline." Baker also examined the type specimen of Pediocactus peeblesianus var. maianus distinguished by L.D. Benson in 1969 and concludes it to belong within P. fendleri. Kartesz (1999), recognized two varieties, var. peeblesianus and var. fickeiseniae, with var. maianus placed in "excluded names". Kartesz (1994), had recognized var. peeblesianus, var. fickeiseniae and ?var. maianus. As of 2013, U.S. Fish and Wildlife Service recognizes Pediocactus peeblesianus var. peeblesianus and Pediocactus peeblesianus var. fickeiseniae. According to ICBN Art. 60.11 see Hunt 2006 the epithet of ssp. fickeisenia is corrected to "fickeiseniorum"

Pediocactus peeblesianus is a perennial cactus that is endemic to Kaibab limestone and gravel soils of Little Colorado paleochannels in North America, in Coconino, Mohave, and Navajo Counties of Arizona. There are two disjunct populations of this species (which were previously known as P. p. ssp. peeblesianus and P. p. ssp. fickeiseniorum); however a recent study examined morphological characters and determined that there was no reason to recognize infraspecific taxa. The population once considered P. p. ssp. peeblesianus is known from three populations of at least 150 plants near Holbrook, Arizona. Pediocactus peeblesianus ssp. fickeiseniorum is widely scattered throughout Kaibab limestone habitat in Coconino and Mohave Counties, and is known from 35-46 populations totaling approximately 2,000 individuals. Significant population declines have been documented at all demography sites established on BLM and Navajo Nation lands throughout the species range, with the exception of the Hellhole Bend monitoring site, where populations are increasing. The major threat to this species is drought, which has led to significant population declines across its range. Additional threats include livestock trampling, off-road vehicles, horticultural collection, gravel mining, rodent predation, invasive species, and possible pollinator limitations.

Pediocactus peeblesianus occurs in western North America where it is endemic to the state of Arizona within Navajo, Coconino, and Mohave Counties (AZGF 2013). The northern population in Mohave and Coconino Counties (previously known as ssp. fickeiseniorum) occurs scattered from Mainstreet Valley in Mohave County to House Rock Valley in Coconino County, along the canyon rims of the Colorado and Little Colorado Rivers, to the area of Gray Mountain, and along the canyon rims of Cataract Canyon on the Coconino Plateau (AZ Ecological Services Field Office 2012). The Navajo County population (previously known as ssp. peeblesianus) occurs near Joseph City and Holbrook (USFWS 2008). Range extent was estimated using NatureServe Network occurrence data from the Navajo Natural Heritge Program and herbarium specimens (for all synonyms) documented between 1984 and 2014 (NatureServe 2024, SEINet 2024).

There are three extant occurrences of Pediocactus peeblesianus ssp. peeblesianus and approximately 46 extant occurrences of P. p. ssp. fickeiseniorum that have been visited since at least 1984 (NatureServe 2024). This may be an overestimate, however, depending on how separation distances and barriers are considered in their delineation. There were 35 extant populations estimated by the U.S. Fish and Wildlife Service in their last five-year review of P. p. ssp. fickeiseniorum (USFWS 2020), using NatureServe's definition of occurrences to define a population.

For this species as a whole, the most significant threat identified is long-term drought, which has led to the population declines, mortality, and low recruitment observed in demography monitoring plots across its range (USFWS 2022, USFWS 2010).

For Pediocactus peeblesianus ssp. fickeiseniorum, other significant human-induced threats to the species and its habitat include off-road vehicles and trampling of plants by livestock (Falk 2007). Populations located both on Bureau of Land Management (BLM) and Navajo Nation lands are open to livestock grazing (USFWS 2013), and at least on population on Navajo Nation has been severely impacted by sheep grazing and use (Willeto 2011). Although populations located on the Navajo Nation largely occur in remote areas of Marble Canyon, car tires and foot traffic have been documented as damaging cacti at some sites, and new roads are continually created, presumably by locals herding livestock. Road maintenance, unauthorized vehicle use, and unauthorized camping has also impacted populations occurring on BLM lands (USFWS 2010). Rodent predation is also a concern, especially in drought years, as well as invasive annual plants such as cheatgrass, red brome, and redstem filaree, which can make up a significant proportion of vegetative cover within P. p. ssp. fickeiseniorum habitat during wet years (USFWS 2013).

For Pediocactus peeblesianus ssp. peeblesianus, threats that led to its initial listing included disturbance by gravel pit operations on private lands, construction of the I-40 highway near Holbrook, and rock collection that could result in trampling of cacti (USFWS 1980). Other potential threats include illegal collection, rodent and rabbit herbivory, and potential impacts from increased off-road vehicle use (USFWS 2022). A majority of the populations near Holbrook occurring on Bureau of Land Management (BLM) lands are fenced to protect cacti, but not all populations are fenced. Additional threats such as low soil moisture and relative humidity, and potential pollinator limitations leading to fruit abortion have been proposed as factors and should be explored further.