argenteus group. Zimmermann (1962) included A. argenteus in the subgenus Alsomys, but this allocation was questioned by Corbet (1978c:136). Based on external, cranial, dental, and chromosomal features, Musser et al. (1996:184) could not place A. argenteus in any existing subgenus of Apodemus and wrote that the species "needs to be compared with other species in the genus within a revisionary study that focuses on phylogenetic analyses of morphological and biochemical characters before we can identify its nearest phyletic affinity." Comparison of genomes among several species of Apodemus, as assessed by differentiation of ribosomal DNA restriction sites (Suzuki et al., 1990), restriction-fragment-length polymorphism (RFLP) of nuclear DNA (Chelomina, 1998; Chelomina et al., 1995), mtDNA cytochrome b sequences (Chelomina et al., 1998b; Liu et al., 2004) and phylogenetic analyses of mitochondrial cytochrome b and nuclear IRBP gene sequences (Serizawa et al., 2000; Suzuki et al., 2003), indicates that A. argenteus differs from all other European and Asian species analyzed, and represents an ancient independent lineage, one of the three initial evolutionary radiations leading to the modern Asian Apodemus fauna (Liu et al., 2004; Serizawa et al., 2000; Suzuki et al., 2003). Its small body size, arboreal adaptations, and distinctive morphology compared with all the other species of Apodemus were also recognized by Thomas (1905b), who described A. argenteus under the name Micromys geisha, and proposed hokkaidi, yakui, and celatus as subspecies of M. geisha (see synonymy in Ellerman and Morrison-Scott, 1951:570). Ellerman (1941:96) also recognized a "geisha group." Kawamura (1989:85; also see Kawamura, 1991) studied molars and cranial fragments of A. argenteus from middle and late Pleistocene sediments as well as Holocene and Recent material, and suggested that the "species is relatively primitive in dental morphology and possibly near to ancestral forms of the genus Apodemus."

Other studies pertinent to systematics of A. argenteus are: electrophoretic analyses of 17 enzymes reported in context of biochemical systematics of Japanese Apodemus (Saitoh et al., 1989), chromosomal and morphometric comparisons between A. argenteus and other Japanese Apodemus (Vorontsov et al., 1977a), polymorphic microsatellite DNA markers identified in A. argenteus that can be used to investigate genetic variation within the species (Ohnishi et al., 1998), study of nonrandom distribution of sister chromatid exchanges (Satoh and Obara, 1995), topographic distribution (Kaneko, 1992a), variation in molar size among samples from the Japanese Oki Isls (Sakai et al., 1997), comparisons with A. sylvaticus and A. speciosus in adaptive latitudinal trends in mandible shape (Renaud and Michaux, 2003), inter- and intraspecific patterns of morphological variation in sympatric A. argenteus and A. speciosus and its importance in insular isolation and biogeographic gradients (Renaud and Millien, 2001), and significance of lower incisor size and shape in ecological and taxonomic inquiries (Millien-Parra, 2000a). Reviewed by Musser et al. (1996) and Kaneko (1994). Because the type series of Mus argenteus Temminck, 1844 is composite, a lectotype was chosen by Smeenk et al. (1982), which stabilizes the name; year of publication of argenteus is usually listed as 1845 but the description appeared in 1844; see Holthuis and Sakai (1970).