Mo. Rev. Stat. § 432.050: Leases, not in writing, operate as estates at will.

All leases, estates, interests of freehold or term of years, or any uncertain interest of, in, to or out of any messuages, lands, tenements or hereditaments, made or created by livery and seisin only, or by parole, and not put in writing and signed by the parties so making or creating the same, or their agents lawfully authorized by writing, shall have the force and effect of leases or estates at will only, and shall not, either in law or equity, be deemed or taken to have any other or greater force.