What is "polyrhachis"

Polyrhachis is a genus of formicine ants found in the Old World with a large number of species (over 600). The genus is yet to be comprehensively resolved and contains many varied species including nest weavers (e.g. Polyrhachis dives), swimming workers (e.g. Polyrhachis sokolova), soil (e.g. Polyrhachis proxima) and tree dwellers (e.g. Polyrhachis bicolor).