The generic distinctness of Diargia and Hyponeura has long been questioned but, because venational characters have largely formed the basis of classification of the higher taxa in the Odonata, authors have been reluctant to admit exceptions and to act contrariwise. The evidence given below leaves little or no doubt that venational differences are not adequate to separate the species of these genera from those of Argia. Diargia is represented by the dwarf bicellulata Calvert, and Hyponeura by two species, the giant type species funckii Selys and the slightly smaller lugens (Hagen).
Gloyd, Leonora K.
"The Synonmy of Diargia and Hyponeura with the Genus Argia (Odonata: Coenargrionidae: Argiinae),"
The Great Lakes Entomologist, vol 1
Available at: https://scholar.valpo.edu/tgle/vol1/iss8/2