What is "subfamilies"

Usage examples of "subfamilies".

And it is my understanding that before the High King Brian and his sire before him invaded Munster and gave everyone a common foe, the various subfamilies of FitzGeralds fought like alley curs amongst themselves, while the non-Norman folk sniped at them almost without cease and rose up in full arms against them whenever it appeared that they might have even a ghost of a slim chance to unseat them.