Musar zu Dewarim 10:9

When taking into consideration Ephrayim and Menashe the sons of Joseph, there are actually fourteen tribes. The land of Israel was divided up amongst only twelve tribes, however. When you deduct from the fourteen tribes the tribe of Levi, which did not qualify for the land distribution, and Joseph himself, who substituted for his father spiritually, you are left with twelve tribes. The land was divided between Reuben, Shimon, Yehudah, Issachar, Zevulun, Dan, Naftali, Gad, Asher, Benjamin, Ephrayim and Menashe.