Kinosternon stejnegeri was considered a subspecies of the Yellow Mud Turtle (Kinosternon flavescens) for six decades, as K. flavescens stejnegeri Hartweg, 1938, and then as K. f. arizonense Gilmore, 1923 (Iverson 1979b, 1989) before being assigned to full species status as Kinosternon arizonense (Serb et al. 2001). Kinosternon arizonense was then synonymized with Pliocene fossil material from Cochise County, Arizona (McCord 2016) and is now considered a separate (extinct) species (TTWG 2021). A partial treatment of the species’ taxonomy was provided by Legler and Vogt (2013). The living form was assigned to Kinosternon stejnegeri, and this is the lineage found today in south-central Arizona and Sonora. It is the sister species to K. durangoense, a species from the Chihuahuan Desert in northern Mexico (Serb et al. 2001, Ernst and Lovich 2009, Iverson et al. 2013), although it is morphologically similar to K. baurii, K. flavescens, and K. subrubrum (Iverson 1991, TTWG 2021). 

Hurtado-Gómez et al. (2024) analyzed phylogeographic structure and taxonomic limits within the genus Kinosternon that demonstrated deep intrageneric divergences; they proposed the recognition of three subgenera: Kinosternon, Cryptochelys, and Thyrosternum. The subgenus Thyrosternum was found to include K. baurii, K. durangoense, K. flavescens, K. steindachneri, K. stejnegeri, and K. subrubrum. TTWG (in press) agrees with this proposed taxonomy.

The Arizona Mud Turtle, Kinosternon stejnegeri, is assessed as Near Threatened under criteria A2c+4c due to a combination of ongoing desertification of the North American hot deserts, senescence of anthropogenic cattle tanks within occupied habitat, lack of confirmed protected localities, and human-induced hydrologic changes. Effects of regional desertification and/or sustained periods of drought are likely to continue to influence and further reduce the species’ habitat, both over the last three generations (ca 51 yrs) and on an ongoing basis as projected into the future for one to two generations, and may also reduce overland dispersal opportunities. The range of K. stejnegeri has been further fragmented by mining, urbanization, and agriculture, and these threats are likely to be exacerbated in the future and synergistically affect the species’ viability. The species' vulnerability is further supported by the NT status of other commensal species, such as the Banner-tailed Kangaroo Rat, with which it is closely associated at one protected location in Arizona. Development along the United States-Mexico border adds additional strain on the species' habitat and the local connectivity of metapopulations. Renewed and focused conservation and restoration measures should focus on habitat protection, strategic restoration of riparian corridors, restoration of cattle tanks in the context of basin-level planning, and management that takes into account desertification, drought, and habitat degradation. The species was previously assessed (as K. arizonense) in 2007 as Least Concern (LC) (Frost et al. 2007).

Kinosternon stejnegeri occurs from Pima County, Arizona, to the vicinity of Tecoripa in central Sonora (TTWG 2021). Its estimated historical indigenous range (area of occupancy, AOO) was ca 36,175 sq. km, and its historical extent of occurrence (EOO) was ca 69,238 sq. km (TTWG in press). An estimate of current AOO of K. stejnegeri using a maximum entropy distribution model (MaxEnt) delineated a larger potential AOO of 105,664 sq. km (Berriozabal-Islas et al. 2020), clearly at odds with the known distribution. The species is generally distributed below 1,000 m asl (Legler and Vogt 2013), and most populations occur at elevations between 200–800 m asl. The species reaches its highest reported elevational occurrence of ca 1,050 m asl in the upper Magdalena basin in Pima County, Arizona, along the border with Sonora (Iverson 1989; Jones et al., unpubl. data). It is generally known from foothill and mountainous areas of interior Sonora; Legler and Vogt (2013) speculated that coastal areas are generally too sandy and porous to support temporary ponds.

Much of what is known about population size, extent, and status of Kinosternon stejnegeri was reported by Iverson (1989) (as K. arizonense), who found the species to be somewhat widespread and common in suitable habitat. Now 35 years later, these parameters have generally not been updated. The originally published localities by Iverson (1989) have not been recently assessed or confirmed. Legler and Vogt (2013) speculated that this species may be more common now because of earthen tank construction. If true, then the species’ trend will closely track the condition and distribution of suitable tank habitat. At least one population in southern Arizona (Jones et al., unpubl. data) appeared relatively stable over two decades, but it is likely connected to and interacting with adjacent demes in Mexico.

Kinosternon stejnegeri has a specialized seasonal ecology strongly driven by the availability of surface water in desert, grassland, and thornscrub ecosystems of southern Arizona and northern Sonora. Populations of K. stejnegeri primarily occur around clusters of anthropogenic, seasonal ponds or “tanks” and has been observed in various types of natural aquatic features such as ditches, arroyos, and washes. When ephemeral rainwater pools are available, K. stejnegeri will utilize those features (Jones et al., unpubl. data). The availability and persistence of seasonal tanks is central to the seasonal ecology of K. stejnegeri; seasonal tanks usually provide the core aquatic environments for foraging and courtship. Arizona Mud Turtles also heavily rely upon adjacent upland habitats for nesting sites, overwintering burrows, and aestivation areas. Burrow complexes of the Banner-Tailed Kangaroo Rat are locally important in Arizona (Jones et al., unpubl. data), and probably elsewhere where the species co-occur. Kinosternon stejnegeri appears to rely on the microhabitats of these terrestrial structures for shelter and thermoregulation. Foraging and feeding habits of K. stejnegeri are poorly documented, though Iverson (1989) indicated that the species feeds on Dytiscid and Hydrophilid beetles as well as odonates, tadpole shrimp and fairy shrimp, and anurans, and speculated that the species feeds diurnally. Legler and Vogt (2013) also described the species as primarily carnivorous, feeding on amphibians, beetles, odonates, and fairy shrimp. Iverson (1989) noted that the species will bask aerially at temperatures as high as 45˚C.

Males average 14.0 cm in straightline carapace length (SCL) and females average 13.6 cm (Berry and Berry 1984). Large males can achieve a SCL of 18.1 cm (Iverson 1989, Legler and Vogt 2013). Legler and Vogt (2013) provided shell ratio data in comparison to other Mexican Kinosternon and Iverson (1989) provided growth data for the species. The smallest turtle found by Jones et al. (unpubl. data) in Pima County, AZ had a SCL of 33 mm. General reviews of the species are provided by Ernst and Lovich (2009) and Legler and Vogt (2013). Sexual maturity in females is reached at ca eight yrs (6–10 yrs; Iverson 1989), yielding an estimated generation time of 16.8 yrs (Iverson 2024). We use 17 years as a reasonable estimate in this assessment.

The main threats to Kinosternon stejnegeri centre primarily on the availability and distribution of surface water. Gradual decline and senescence of cattle tanks will result in local extirpations where tanks are not maintained. Historically the species was also affected by habitat loss and habitat degradation caused by development and agricultural conversion, but these patterns have not specifically been evaluated or quantified for this species. Hydrological changes (Owen-Joyce et al. 2021) associated with tank deterioration (Nichols et al. 2018) and a consistent drying trend (Seager et al. 2007, Williams et al. 2020) threaten K. stejnegeri just as it is causing declines in other chelonians (Lovich et al. 2014). These activities fragment and degrade the turtle's habitat, impacting its survival and reproductive success.

Climate change represents a multifaceted threat by disrupting the balance of desert and tropical ecosystems, as well as ecohydrology. According to a modelling study by Berriozabal-Islas et al. (2020), climate change may affect K. stejnegeri, potentially leading to a reduction in its currently estimated potential AOO of 105,664 sq. km to 89,304 sq. km, signifying a decrease of up to ca 15% by 2070 in an extreme global warming modelling scenario such as RCP85 (Representative Concentration Pathway 8.5). However, their estimates are somewhat suspect as they also estimated an AOO much larger than the currently known distribution. Currently, there is no evidence of significant commercial use or trade negatively impacting the species, but vigilance is needed to monitor and prevent potential exploitation. The negative effects of introduced species is not well documented, but the bullfrog (Rana catesbeiana) and other introduced species are likely predators of young turtles. Subsidized mammalian predators, pathogens, pollution, development, and fragmentation associated with USA–Mexico border installations also pose threats to the persistence of local populations.

There is no current or substantial evidence to indicate that Kinosternon stejnegeri is being targeted for illegal trade or is commercially traded. The species does not appear to be used commercially in any significant way. However, the current absence of evidence of an illegal trade does not demonstrate the absence of a potential threat in the future. If the global demand for North American turtles in the pet trade persists there is a reasonable possibility that K. stejnegeri could become a target in the future. Monitoring and regulation of the pet trade, both at state and international levels, as well as at key protected sites, remains essential to mitigate illegal collection if and when it is documented to occur.

Kinosternon stejnegeri is listed in CITES Appendix II as of 2023 as Kinosternon spp. Turtles in general are protected from exploitation under Mexican wildlife and natural resource legislation; implementation is uneven and in places better enforcement is probably needed. As an aquatic or semiaquatic species occurring in an extremely austere climatic zone, its persistence can only be considered tenuous. Full protection from all depredation except scientific study should be provided, and sanctuaries should be established where habitat destruction can be prevented (Smith and Smith 1979).

There are few protected areas in Sonora within the known range of K. stejnegeri, though it may occur in the Sistema de Presas Abelardo Rodríguez Luján–El Molinito outside Hermosillo and perhaps in El Pinacante y Gran Desierto de Altar Biosphere Reserve. It also occurs in Organ Pipe Natural Monument (IUCN Cat.III, 134 sq. km.) in Arizona, and perhaps in Cabeza Prieta National Wildlife Refuge (Cat.IV, 3480 sq. km), and in the Buenos Aires National Wildlife Refuge. The species apparently benefits from humans constructing ponds within its range.

Across most of its range, K. stejnegeri has relatively few conservation measures in place. Where it benefits from conservation action is mostly the result of targeted actions for other species, such as tank restoration for the Chiricahua Leopard Frog. Managers of sites with known occurrences of K. stejnegeri should prioritize the restoration and maintenance of human-made tanks and ponds known to support the species and ensure adequate buffers to protect adjacent upland areas occupied by the species. Small and oftentimes isolated  ponds frequently serve as essential habitat for the species. Kinosternon stejnegeri would also benefit from wildlife accommodations along the US-Mexico border, including wildlife passages in border fencing and passage structures under roadways frequently used by border agents. Furthermore, it is important to enhance conservation efforts within protected areas, such as Buenos Aires National Wildlife Refuge, where the species is known to occur. Whether the species occurs as a viable population in Organ Pipe Cactus National Monument, Arizona, is unclear.

Additional research into the species distribution, demographic trends, habitat use, space needs, dispersal, and inter-annual site fidelity is needed, as is international coordination in the border region and across the species’ range to evaluate range-wide patterns and trends.