Known Tribes and Known Members
The Jetstone Tribe
The Nearly-Lost Plaid Tribe
The Lost Croatan Tribe
Parson says tribal affiliations seem "cultural," and have no real meaning.Erf-b1-p079a I think this means that sides don't depend on tribal affiliation to determine their unit makeup, or who leads, or whatever. Also, casters will often be on sides that don't match their tribes. Tribes are almost certainly involved, though, for Royals and Heirs.
A side may be composed of a main, or central, tribe, and its collective allies. For instance, Gobwin Knob had 200 living troops - these, perhaps, were all or mostly the remnants of the Plaid Tribe. Considered against the masses of Uncroaked, the Dwagons, the Twolls, and the Golems, along with their Natural Allies, the Gobwins and Hobgobwins, the Plaid Tribe is a fraction of their side, but it is perhaps the central thread, as it were.
Tribes in the Real World have familial, or genetic, ties. Though no one in Erfworld is technically related, and heirs don't necessarily resemble their "parent," it is possible that members of a tribe share certain characteristics, or at least are more likely to... then again, what do Stanley and Sizemore have in common?
The different elf varieties may be based on tribal divisions.