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There are many mentions of the "12 tribes" (e.g., the tag of this question). But there really were 13: Ya'akov had 12 sons, of which each was the ancestor of one tribe except Yosef that was the ancestor of 2.
I know that there were 12 tribal territories because Levi had no land of its own. But on the other hand, Levi had its own symbol while Yosef only had one symbol (see question and picture). But AFAIK nobody ever mentions a "Yosef tribe".
So what 12 tribes are usually meant?