Key to species of subgenus Rhoenanthus (Potamanthindus): male imago (male of R. sapa unknown)

1 Penes relatively stout, clearly shorter than half of forceps (Fig. 9)............................................... 3

- Penes relatively slender, longer than or subequal to half of forceps (Fig. 6C, 6F)................................... 2

2 Outer half wings stained with purplish brown pigments, penis forked apically in ventral view (Fig.6 E–F).......... R. youi

- Wings stained with purplish brown pigments near leading margins and midregion (Fig. 6 A–B); apex of penis unforked in ventral view (Fig. 6D)......................................................................... R. hunanensis

3 Forewings with purplish brown stained markings throughout wing.................................... R. magnificus

- Forewings with purplish brown stained markings concentrating transversely in midregion and leading margin........... 4

4 Penes broad, separated........................................................................ R. coreanus

- Penes relatively slender, fused basally............................................................ R. obscurus