These are the tribes in which you can create or adopt elves, other than the main tribe:
Children of the Oaks
A tribe of plainsdwelling purebloods with copper-colored skin (and mohawks!).
Elves of the Frozen Lands
Fox-blooded elves from a land far north that's always covered in snow.
The Spotted Paw Clan
Cheetah-blooded elves who live on a far off savannah...and who might be going through a tragedy quite soon.
All green names indicate elves who've already been somewhat played or mentioned in-game. They are in other words "adoptables". Still, they have next to no CIS (Character Information Sheet), so you get to make up a lot about their personality/skills/apperance, etc.
You can of course make up your very own elf from these tribes, as long as you don't create more elves than the tribe has room for!
Example: No more elves can come from the Branch of Stars, since it's full. You can however adopt an elf from the Branch of Stars.