California Code, Corporations Code - CORP § 5612

If a membership stands of record in the names of two or more persons, whether fiduciaries, members of a partnership, joint tenants, tenants in common, spouses as community property, tenants by the entirety, or otherwise, or if two or more persons (including proxyholders) have the same fiduciary relationship respecting the same membership, unless the secretary of the corporation is given written notice to the contrary and is furnished with a copy of the instrument or order appointing them or creating the relationship wherein it is so provided, their acts with respect to voting shall have the following effect: