California Code, Water Code - WAT § 20568

The holder of title to an undivided interest in any land may sign any petition provided for in this division.  Undivided interests shall be counted and valued as though they were separate interests.  If the assessment book fails to indicate the extent of any undivided interest, the holders of title whose undivided interests in any land are not specifically defined have, for the purposes of this division, equal shares therein.