In their broad specific concept, Jarrell and Fredga (1993) viewed all North American taxa, except D. hudsonius, as junior synonyms, including the insular forms exsul and vinogradovi. Morphological, distributional, breeding, chromosomal, and-or molecular evidence, albeit uneven and incomplete, persuades us to maintain D. nelsoni, D. nunatakensis, D. richardsoni, D. unalascensis, and D. vinogradovi as distinct (see those accounts).
Standard and banded chromosomal comparisons reported by Borowik and Engstrom (1993), who supported the synonymy of clarus and lentus. Engstrom et al. (1993) reported kilangmiutak (2n = 47-50) as karyotypically separable from D. groenlandicus (2n = 38-44), calling them "cytospecies," but found the two to be only marginally differentiated in mitochrondrial DNA sequences; samples drawn from the range of kilangmiutak are morphometrically (Eger, 1995) and genetically (Ehrich et al., 2000) unremarkable in comparisons with D. groenlandicus proper. The form rubricatus (Beringian distribution) shares a distinctive XY-autosomal fusion pattern with D. groenlandicus (Pearyland distribution), different from that found in D. richardsoni (Borowik and Engstrom, 1993); levels of differentiation in cranial form (Eger, 1995) and nucleotide sequences (Ehrich et al., 2000) provide no persuasive evidence for specific separation of rubricatus, although the latter study did disclose weakly defined western and eastern clades divided by the Mackenzie River.