Formerly included couesi and related forms as subspecies (see account of O. couesi). Geographic variation evaluated by Humphrey and Setzer (1989), who acknowledged the nominate and only one other subspecies, O. p. natator; Whitaker and Hamilton (1998), on the other hand, regarded the island taxa planirostris and sanibeli as valid subspecies and viewed natator as indistinguishable from nominate palustris, observing their philosophical emphasis of overwater gaps as "primary isolating mechanisms" rather than renewed data analyses. Overwater dispersal capability studied by Forys and Dueser (1993) in the context of understanding differentiation of populations on near-shore islands. Recoveries from sub-Recent archeological and cave excavations document the species substantially to the north (E Nebraska to SW Pennsylvania) of its present range limits (see Graham and Lundelius, 1994; Richards, 1980).
The form argentatus was described as a species from the lower Florida Keys (Goodyear and Lazell, 1986; Spitzer and Lazell, 1978), later synonymized under O. palustris natator (Humphrey and Setzer, 1989), and pointedly reinstated as a species (Goodyear, 1991). Its status continues to oscillate in faunal works (or reviews thereof), unilluminated by fresh data or reanalysis (e.g., a species, as per Lazell, 1993, and Whitaker and Hamilton, 1998; not a species, as per Brown, 1997, and Rose and Dueser, 1999). We continue to follow Humphrey and Setzer (1989) because of their better measurement protocol, larger sample sizes, broader geographic and taxonomic scope, stronger analytical rigor that accounts sources of nongeographic variation, and firmer grasp of the biological and paleogeographic contexts. As an anecdotal aside, based on few specimens reviewed and not to be confused with scientific process, we cannot separate the crania of argentatus from those of O. palustris with the same confidence that one can sort O. palustris from O. couesi or O. nelsoni. In light of the subspecific endemism displayed among other Florida‑Key mammals, the status of argentatus merits further study drawing upon genetic evidence; the investigatory tools and data sources appropriately sensitive to this taxonomic question are at hand and merely await application. See Wolfe (1982, Mammalian Species, 176).