The testacea species group is Holarctic in distribution. Currently, this group contains four described species, all of which are mycophagous. Grimaldi et al. (1992) examined the systematic relationships within this clade. They suggested that there were two major lineages, the testacea and putrida subgroups. The testacea subgroup contains three species: D. testacea, D. orientalis, and D. neotestacea. Drosophila putrida is the only species placed in the putrida subgroup. Grimaldi et al. (1992) suggested this placement because of the highly different male genitalia of D. putrida. Perlman et al. (2002) finds a similar topology, although their phylogeny is more resolved than the previous work in that it supports the sister group relationship between D. orientacea and D. testacea.
(excerpted from Markow and O’Grady, 2006, Chapter 1)
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