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The taxonomy of the subgenus Ashima of the genus Phortica is revised. A cladistic analysis of 66 morphological characters is conducted, covering 35 species (28 known and 7 new species: Phortica efragmentata sp. nov., P. andreagigoni sp. nov., P. watabei sp. nov., P. halimunensis sp. nov., P. akutsui sp. nov., P. kerinciensis sp. nov., and P. takehiroi sp. nov.) which correspond to 71.4% of 49 total spp. of Ashima. The resulting cladogram shows that the studied species are separated into several clades/subclades/cluster each highly supported with specific synapomorphies. Those clades/subclades/cluster are newly defined as the following species groups, subgroups or complex: the afoliolata, foliiseta, nigrifoliiseta and angulata species groups; the foliiseta, tanabei, nigrifoliiseta and glabra species subgroups; and the foliiseta species complex. The subgenus Ashima is peculiar in having the asymmetric male genitalia as the ground plan and showing the antisymmetry (i.e. intraspecific mirror-image variation) in some species but the directional asymmetry (i.e. side-fixed asymmetry) in others. The evolution of genital asymmetry in this subgenus is estimated by mapping the states (symmetry, directional asymmetry and antisymmetry) of bilateral structures of male genitalia on the cladogram. This ancestral state reconstruction estimates that the directional asymmetry of male genitalia has evolved at the ancestor of this subgenus and then changed to the antisymmetric state independently in two lineages, the angulata + nigrifoliiseta species groups and the foliiseta species complex. In this study, a standardized terminology recently proposed for the male terminalia of Drosophila melanogaster is extendedly adopted to describe the morphology of male terminalia in the subgenus Ashima, one group of the subfamily Steganinae.