Kinosternon subrubrum historically included three subspecies (K. s. subrubrum, K. s. hippocrepis, and K. s. steindachneri), however, K. s. steindachneri has recently been recognized as a distinct species (TTWG 2021). Furthermore, unpublished genetic studies suggest that K. s. hippocrepis may be divergent enough to merit full species status (J.B. Iverson, unpubl. data). Two subspecies are currently recognized: Kinosternon s. subrubrum (Bonnaterre, 1789) and K. s. hippocrepis Gray, 1856. Testudo subrubra was first used by Lacépède, 1788, but this name was made unavailable by ICZN (1987, 2005) suppressing Lacépède's work as non-binomial.

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.

While perhaps locally impacted, Kinosternon subrubrum is widespread, generally quite abundant in a variety of aquatic habitats, occurs in adequate protected areas, and is not under specific exploitation pressure; overall the species is demonstrably secure. It is therefore listed as Least Concern (LC). The historical range estimated for K. subrubrum is large and the species is currently found in numerous protected areas. The previous IUCN assessment in 2011 also listed this species as LC (van Dijk 2011). The current assessment generally agrees with the past assessment as this species often exhibits large population sizes in modified habitats with high densities, such as farm ponds and drainage ditches. Populations in the core of the range are likely not to experience significant declines or suffer from major exploitation threats beyond road collisions, habitat loss to local development, and destruction of nests from predators. The populations at the periphery of its geographic range are of the most concern, especially those in Indiana, Kentucky, Pennsylvania, and New York, where it is a listed species in those states.

Kinosternon subrubrum is distributed in the United States along the eastern Coastal Plain from New York in the Northeast, Georgia and northern Florida in the South, and throughout the Gulf Coast Plain to eastern Texas in the Southwest, north to central Oklahoma, and in the Mississippi Valley to Illinois and Indiana in the Midwest (TTWG 2021). The estimated historical indigenous range (area of occupancy, AOO) for the species K. subrubrum was 1,401,264 sq. km (TTWG 2021), and the estimated historical indigenous extent of occurrence (EOO) was 2,489,041 sq. km (TTWG in press).

Kinosternon subrubrum subrubrum is distributed in the United States along the eastern coastal plain from New York in the Northeast, Georgia and northern Florida in the South, and east to central Mississippi and north in the Midwest along the Mississippi River to southern Illinois and along the Wabash River in Indiana (TTWG 2021) (see Figure S1 in the Supplementary Information). The estimated historical indigenous range (area of occupancy, AOO) for the subspecies K. s. subrubrum was 819,921 sq. km (TTWG 2021), and the estimated historical indigenous extent of occurrence (EOO) was 1,544,395 sq. km (TTWG in press).

Kinosternon subrubrum hippocrepis is distributed in the United States in the western portion of the southern Mississippi Valley, along the Gulf of Mexico in Texas, north to central Oklahoma, and along the Mississippi River north to southern Illinois in the Midwest (TTWG 2021) (see Figure S1 in the Supplementary Information). The estimated historical indigenous range (area of occupancy, AOO) for the subspecies K. s. hippocrepis was 682,552 sq. km (TTWG 2021), and the estimated historical indigenous extent of occurrence (EOO) was 1,131,025 sq. km (TTWG in press).

Population densities of Kinosternon subrubrum vary widely and depend on the habitat, with ponds in agricultural areas exhibiting the highest densities. In Arkansas, generally, population densities ranged 17–260 turtles/ha (Trauth et al. 2004). In a farm pond in South Carolina, density was 8.2 turtles/ha (Congdon et al. 1986), 22–56 turtles/ha in the Carolina Bay in South Carolina (Gibbons 1983), 64 and 104 turtles/ha in a creek in Oklahoma (Mahmoud 1969), 58–160 turtles/ha in Alabama farm ponds (Scott 1976), 470 turtles/ha in a fertilized farm pond in Alabama (Stone et al. 1993), and 33–92 turtles/ha in ponds in southeastern New York (Larese-Casanova 1999). Population size from a 10-year study in a 10-ha bay in South Carolina was estimated at 371 turtles (range, 224­–556 turtles) (Gibbons 1983). Biomass was estimated to be 0.7 kg/ha in a 1.1-ha pond and 3.7 kg/ha in the 10-ha Carolina Bay in South Carolina (Congdon et al. 1986), 2.1–11.1 kg/ha in ponds in New York (Larese-Casanova 1999), and 25.9 kg/ha in a creek in Oklahoma (Iverson 1982). In North Carolina, Failey et al. (2007) found that this species comprised 10.4% and 3.5% of all turtles (six species), and 100% and 67% of all kinosternids in golf course and farm ponds, respectively. This species totalled 4.4% of all turtle captures (and 26.3% of all kinosternid captures) in Texas (Riedle et al. 2015), and 9.2% of kinosternid turtles and 1.1% of all aquatic turtles traversing or attempting to traverse a road that bisected a lake in northwestern Florida (Aresco 2005). In Arkansas, it was just 2% out of over 4,000 captures in a turtle assemblage of nine species (Massey 2021). During 30 years in South Carolina, J.W. Gibbons had 9,797 captures of this species, which comprised 50% of all turtle captures, whereas this species has small population sizes and is considered State Endangered in Indiana (Ernst and Lovich 2009).

Current Population Trend: Variable. Stable to increasing in range core, but stable to decreasing in range margins, particularly in Indiana where it apparently has not been seen in some time (Minton 2001) and in Pennsylvania where it was thought to be extirpated until 2008 (Ruhe and LaDuke 2011).

Habitat: Aquatic habitats of K. subrubrum include shallow and slow-moving or lentic freshwater systems with heavy vegetation (Meshaka and Gibbons 2006, Meshaka et al. 2017). The species also occupies brackish marshes and barrier islands (Gibbons and Coker 1978), where it can tolerate a salinity level up to 8.5 PPT (Abubakar 2017). In general, it prefers shallow, vegetated water bodies, where it typically stays near the shore (Riedle et al. 2009, 2015; Scott 1976). This species has also been found in association with sandy-bottomed creeks, slow-moving streams, marshes, sloughs, canals, beaver ponds, farm ponds, golf ponds, vernal woodland pools, swamps, and drainage ditches (Palmer and Braswell 1995, Failey et al. 2007, Harden et al. 2009, Homyack et al. 2016). This species avoids fast-flowing rivers, streams, and spring runs (Ernst and Lovich 2009). Overwintering sites include aquatic and terrestrial habitats, sometimes far from water. In Maryland, turtles overwintered 55–224 m from the edge of the wetland (Cordero et al. 2012), up to 600 m in South Carolina (Bennett et al. 1970), and an average of 72 m for an average of 107 days in Georgia (Steen et al. 2007). The length of hibernation is positively correlated with latitude with a range from 220 days in New York (Larese-Casanova 1999) to 70 days in Alabama (Scott 1976). Nest site habitats are usually open ground not far from water, with sandy or loamy soils preferred, but piles of vegetative debris, the pulp of downed logs, and muskrat or beaver burrows can be used (Ernst and Lovich 2009).

Diet: Kinosternon subrubrum is omnivorous with primarily carnivorous tendencies. Its diet, which includes aquatic vegetation, insects, spiders, crustaceans, molluscs, crayfish, seeds, frogs, snails, carrion, and earthworms, is similar in widely separated populations (Meshaka et al. 2017).

Longevity: Longevity in the wild exceeds 30 yrs (Gibbons 1983, Parker 1996). In South Carolina, individuals were projected to live 20 to 50 years (Frazer et al. 1991). Longevity records in captivity include a turtle acquired as an adult that lived 18.3 yrs (Snider and Bowler 1992, Slavens and Slavens 2000) and a female that lived 38 years which was also acquired as an adult (Pope 1939).

Reproductive ecology: Incubation time lasts about 90–100 days and is negatively correlated with latitude (Meshaka and Gibbons 2006, Meshaka et al. 2017). Clutch size varies 1–9 eggs (mean = 3.2 eggs, n = 84) (Ernst and Lovich 2009) with larger clutches being more common in northern populations (Meshaka et al. 2017). In South Carolina, Wilkinson and Gibbons (2005) found a mean clutch size of 3.4 eggs and eggs had a mean width of 15.2 mm, which came from 635 females that had a mean plastron length (PL) of 87.5 mm. Individuals lay, on average, 2.2 clutches annually (n = 15 females) (Ernst and Lovich 2009), and in eastern Texas, K. s. hippocrepis was found to produce up to four clutches annually (n = 3 females) (Houseal and Carr 1983). Interval between clutches is about 30 days (range = 9–66 days), with about 75% of females in a population reproducing in any given year (Gibbons 1983, Frazer et al. 1991). Females may retain clutches 26–50 days before laying eggs (Buhlmann et al. 1995). Eggs range 16.3–32.2 mm in length (mean = 25.7 mm, n = 62), 12.7–20.0 mm in width (mean = 15.7 mm, n = 59), and 3.0–3.9 g in weight (mean = 4.3 g, n = 10) (Iverson 1979, Ernst and Lovich 2009). Hatchlings range 16.6–27.0 mm in straightline carapace length (SCL) (mean = 22.4 mm, n = 36), 15.0–21.5 mm in PL (mean = 19.1 mm, n = 36), and 2.9–4.0 g in weight (mean = 3.6 g, n = 10) (Iverson 1979, Ernst and Lovich 2009). In South Carolina, hatchlings overwinter in the nest and emerge the following spring (Gibbons and Nelson 1978).

Size: Size (maximum straight-line carapace length, SCL): male 116 mm, female 125 mm (Meshaka et al. 2017). In Oklahoma, the species usually matures at an SCL of 80–120 mm, with males 4–7 years and females 5–8 years of age (Ernst and Lovich, 2009). Both sexes mature in 4–6 years at 70–80 mm SCL in South Carolina (Frazer et al. 1991, Gibbons 1983) and nine years in New York (Larese-Casanova 1999). Maturity in Arkansas female K. s. hippocrepis is at 80–85 mm SCL and 6–8 yrs (Iverson 1979). As such, if we assume sexual maturity at ca 6–8 yrs, then generation time can be estimated as ca 12–14 yrs (Iverson, 2024).

Individuals and populations of Kinosternon subrubrum are affected by habitat destruction, road mortality, and pesticide poisoning. Predators include kingsnakes (Lampropeltis), opossums (Didelphis), raccoons (Procyon), crows (Corvus), gar (Lepisosteus), and blue crabs (Callinectes) (Ernst and Lovich 2009). Winzeler et al. (2015) reported Ranavirus-associated morbidity and mortality in an individual from South Carolina.

Kinosternon subrubrum is uncommon in the pet trade, and it is not consumed regularly. Massey (2021) found that commercial harvesting had no perceptible impact on this species across three years of trapping in agricultural ditches and aquaculture ponds in Arkansas.

Kinosternon subrubrum is subject to a variety of State legislation and regulations. The species is listed as Kinosternon spp. in CITES Appendix II as of 2023. It is found in many protected areas and listed (threatened, endangered, or species of conservation concern) in several states where it occurs (Table 1 in Meshaka et al. 2017): it is State Endangered in Indiana, Pennsylvania, and New York, and Species of Greatest Conservation Need in Kentucky.