Oryzomyini. A taxonomically complex and nomenclaturally confused taxon whose definition was successively broadened by Goldman (1918), Tate (1932d, e), and Ellerman (1941). By the time of Cabrera (1961), the genus embraced as subgenera Melanomys, Microryzomys, Nesoryzomys, Oecomys, and Oligoryzomys—a polyphyletic agglomeration of taxa as evolutionarily divergent from one another, and from Oryzomys sensu stricto, as Neacomys is from Nectomys, forms traditionally accorded generic status (see Carleton and Musser, 1989:52). Others have recognized some or all of these as genera (e.g., Carleton and Musser, 1984, 1989; Gardner and Patton, 1976; Gyldenstolpe, 1932; Reig, 1981, 1984; Thomas, 1917c), as we continue to do here; see appropriate generic accounts for taxonomic histories.

Notwithstanding the elevation of the aforementioned genus-group taxa, the generic boundary as denotatively conveyed by the species listed here remains a polyphyletic shell. The species may be morphologically and-or geographically sorted into the following groups whose relationship to one another and to other oryzomyine genera is incompatible with their continued association under a single genus: Albigularis complex (albigularis, auriventer, caracolus, devius, keaysi, levipes, meridensis); Balneator (balneator); Chapmani complex (chapmani, saturatior); Hammondi (hammondi); Megacephalus complex (megacephalus [laticeps, megacephalus, perenensis, suazensis] and yunganus [tatei, yunganus] species groups); Nitidus complex (Transandean [alfaroi, bolivaris, melanotis, rhabdops, rostratus, and talamancae] and Amazonian-Atlantic Forest [emmonsae, kelloggi?, lamia, legatus, macconnelli, nitidus, and russatus] species groups); North and Central American Oryzomys sensu stricto (couesi, dimidiatus, gorgasi, nelsoni, and palustris); and the very heterogeneous residuum of South American "Oryzomys" (angouya, galapagoensis, maracajuensis, marinhus, polius, scotti, subflavus, and xanthaeolus). See discussions in Carleton and Musser (1989), Carleton and Olson (1999), and Voss et al. (2002) on the need to objectively represent the monophyly and diagnosis of Oryzomys sensu stricto as elementary to improving comprehension of orzyomyine phylogeny. See Weksler (2003) for molecular evidence that pointedly underscores the polyphyletic contents of the genus as currently arranged.

Karyotypic information for many species supplied by Baker et al. (1983), Gardner and Patton (1976), and Haiduk et al. (1979); multispecific molecular surveys and extended taxonomic commentary provided by Patton et al. (2000), Bonvicino et al. (2001), and Weksler (2003); for morphological surveys, see Carleton (1973, 1980), Hooper and Musser (1964a), Musser et al. (1998), Voss and Linzey (1981), and Voss et al. (2001); for overview of habitat and distribution, see Sánchez-Cordero and Valadez-Azua (1989). Much basic alpha-level revision yet required.