Chromosomal and molecular evidence relates M. rufocanus most closely to Korean M. regulus and Japanese M. rex, M. andersoni, M. smithii, and M. imaizumii (Iwasa et al., 1999a; Suzuki et al., 1999b; Wakana et al., 1996); it is also morphologically similar to the Chinese M. shanseius (see that account). Allozymic (Mezhzherin and Serbenyuk, 1992) and chromosomal data (Sokolov et al., 1990) reveal M. rufocanus as highly differentiated from other Myodes sampled (M. centralis, M. glareolus, M. gapperi, M. rutilus). DNA/DNA hybridization and homologous landmark analyses also distantly isolate M. rufocanus from M. glareolus and New World M. rutilus and M. gapperi (Din et al., 1993). Myodes rufocanus and M. rex have rooted molars (in adults), but their purported close relatives—M. andersoni, M. smithii, and M. imaizumi from the main Japanese islands, and M. shanseius and M. regulus from mainland China and the Korean Peninsula, respectively—have rootless molars. These data collectively presume that aquisition of ever-growing molars occurred independently from a rooted rufocanus like ancestor in insular regions and on the continent, a distributional pattern in a significant dental innovation unlike that observed among other species of Myodes.

Morphological variation broadly assessed by Kaneko (1990), who documented morphological distinctions between M. rufocanus and the Korean endemic M. regulus (as Eothenomys). Geographic distribution of chromosomal variation across continental E Russia, Sakhalin Isl, and other small islands assessed by Kartavtseva et al. (1998), who recorded a conservative 2n (56) but a variable FN (56-59); Hokkaido sample also chromosomally similar to continental species (Obara et al., 1995) ; phylogenetic analyses of chromosomes and allozymes undertaken by Yoshida et al. (1989) for Japanese populations. Contrasting phylogeographic patterns, based on cytochrome b versus Sry gene, documented among populations from E Russia, Sakhalin Isl, and Hokkaido and offshore islands (Iwasa et al., 2000). M3 variation reported by Abe (1982). Cranial skeleton and myology associated with incisal biting and mastication examined by Satoh (1997, 1998, 1999) and compared with the murine Apodemus speciosus; cardiac musculature of the pulmonary vein and vena cava described by Endo and Yanagawa (1994). Ishibashi et al. (1992) used DNA fingerprinting to track individual relatedness during cyclic fluctuations in population density so common to M. rufocanus.

European distributions reviewed by Henttonen and Viitala (1982), Korean by Won and Smith (1999). Occurrence on the Svjatoj Nos peninsula and isthmus in Lake Baikal documented by Reiter et al. (1995). Kaneko et al. (1998) extensively covered the systematics and distribution of M. rufocanus on Hokkaido; the species occurs on Haikkado and those offshore islands separated only by narrow and shallow straits, but no extant population occupies Oshima Isl, separated from the coast of Hokkaido by a wide and deep strait (Iwasa et al., 2000). In the E Palearctic, the range of M. rufocanus is separated from Chinese species of Eothenomys by the Gobi Desert (Kaneko, 1992c).

Tokuda (1935) described sikotanensis (Shikotan Isl in the Kurile islands) and proposed the genus Neoaschizomys to contain it (in 1941, he transferred these to Clethrionomys). Imaizumi (1949) described akkessi from Daikoku Isl (near SE Hokkaido) as a subspecies of sikotanensis; the nomen nudum status of microtinus, associated with sikotanensis, is discussed by Gromov and Polyakov (1977) and Pavlinov and Rossolimo (1987). Although sikotanensis is frequently recognized as a distinct species (Gromov and Erbajeva, 1995; Gromov and Polyakov, 1977; Imaizumi, 1971, 1972; Musser and Carleton, 1993; Pavlinov and Rossolimo, 1987, 1998; Pavlinov et al., 1995a), chromosomal and molecular samples from these islands, and other reported insular occurrences, are unremarkably aligned with M. rufocanus (Mezhzherin and Serbenyuk, 1992; Sokolov et al., 1990; Wakana et al. 1996). Kaneko et al. (1998) reported that the holotype of sikotanensis is lost but original molar illustrations, especially the M3, match those of M. rufocanus, not M. rex; they too concluded that sikotanensis is another insular example of M. rufocanus, a view consistent with the vole’s overwater dispersal ability (Iwasa et al. 2000).