Subgenus Alexandromys. Earlier included in the subgenus Pallasiinus (Gromov and Erbajeva, 1995; Pavlinov and Rossolimo, 1998; Pavlinov et al., 1995a; Zagorodnyuk, 1990), also containing M. montebelli and M. limnophilus, or arranged in subgenus Microtus (Gromov and Polyakov, 1977; Pavlinov and Rossolimo, 1987). Based on morphometric, chromosomal and hybridization analyses, Meyer et al. (1996) placed M. oeconomus in a clade containing M. middendorffii, M. mongolicus, M. fortis, M. sachalinensis, M. maximowiczii, M. jujanensis, and M. evoronensis; according to phylogenetic analysis of cytochrome b sequences, member of a clade that includes the Taiwanese M. kikuchii as sister-species, along with M. montebelli, M. middendorffii, and M. fortis (Conroy and Cook, 2000a). Close alliance of M. oeconomus and M. montebelli is also supported by pairing patterns of X-Y chromosome (Borodin et al., 1997).

Homogeneity of Old and New World populations averred by Zimmerman (1942) and sustained by subsequent studies (Nadler et al., 1976, 1978; Ognev, 1964; Rausch, 1953; Conroy and Cook, 2000a). Interpretations of mitochondrial DNA led Conroy and Cook (2000a) to propose that M. oeconomus represented one of only two colonizations of North America by Old World stocks, the earlier one radiating into the North American endemics. Allozymic and chromosomal differentiation among subspecies surrounding the Bering Strait minimal, also suggesting a relatively late entry of the species into North America and rapid expansion of populations once arrived (Lance and Cook, 1998).

Geographic variation and subspecies of Nearctic populations reviewed by Paradiso and Manville (1961), populations in Russia and adjacent regions by Gromov and Erbajeva (1995), and European populations by Tast (1982b) and Mitchell-Jones et al. (1999). Chromosomal data evaluated by Zima and Kral (1984a); Modi (1987) and Lance and Cook (1998) documented recent chromosomal results (uniformly 2n = 30, FN = 54). Synaptic association of sex chromosomes and its evolutionary significance discussed by Ashley and Fredga (1994). Gastrointestinal morphology of Chinese sample and its adaptive significance reported by Wang et al. (1995). Interdependence and correlation among non-metric characters with sex, age, and body size evaluated by Markowski (1995). Molar patterns intensively investigated, addressing frequency and interpretation of morphotypes in large isolated sample from W Poland (Rachowiak, 1993), assessment of variation in extant samples against which patterns in extinct species can be judged (Angermann, 1984), correlation of variation with latitude and altitude (Pozdnyakov and Litvinov, 1994), and departures from bilateral symmetry (Kovaleva et al., 2002).

Kaneko and Hasegawa (1995) identified M. oeconomus from a late Pleistocene cave on Miyako Isl, Ryukyu Isls, an occurrence far outside the modern and Pleistocene distribution as known by other fossils. They also allocated Pleistocene epiratticeps as another synonym of M. oeconomus. The taxon corneri, based on Pleistocene (Late Glacial) cave deposits in the British Isles, testifies the former presence of M. oeconomus (Berry, 1996; Yalden, 1999).

Ognev (1964) identified ratticeps Keyserling and Blasius, 1841, as the proper name applicable to this species, and suggested that oeconomus Pallas, 1776, was based upon an example of M. gregalis. Ellerman and Morrison-Scott (1951:705), however, noted that kamtschaticus Pallas, 1779, would be the oldest name, not ratticeps, if Ognev is correct (also see Hall, 1981:805). While most systematists continue to utilize oeconomus Pallas, 1776, for reasons of familiarity, ratticeps has been used in the past (G. M. Allen, 1940) and even recently (Berry, 1996). This nomenclatural uncertainty requires formal resolution.