Rule 903.5d

A card with a basic land type may be included in a Commander deck only if each color of mana it could produce is included in the commander’s color identity. Example: Wort, the Raidmother’s color identity is red and green. A Wort Commander deck may include land cards with the basic land types Mountain and/or Forest. It can’t include any land cards with the basic land types Plains, Island, or Swamp.