Mo. Rev. Stat. § 534.230: Extent of claim of person having lawful possession.

When any forcible entry and detainer, or unlawful detainer, shall be made upon any lands or other possessions, against the provisions of this chapter, the person having the lawful possession, shall, against the wrongdoer, be considered as entitled to such quantity, extent and limits of lands as by the patent, grant, concession, deed, survey, donation, settlement or preemption right, such person or those under whom he claims can, by the laws of the United States or of this state, have and lawfully claim in and to such premises.