Md. Code, Tax-Prop. § 14-852
When land is sold to pay county or State taxes, or both, assessed on the land and in default, and the owner of the land at the time of the tax sale, the owner's heirs, devisees, or assigns, severally, jointly or in continuous successive ownership have held the land sold in adverse possession for 7 years after the final ratification of the tax sale and before action or suit is brought, and prosecuted by the purchaser at the tax sale, the purchaser's heirs, devisees, or assigns to obtain possession of the land, the possession is a bar to all right, title, claim, interest, estate, demand, right of entry, and right of action of the purchaser or the purchaser's heirs, devisees, or assigns derived from the tax sale as to the land held in possession. This section applies to all tax sales except for tax sales made and ratified on or before the 1st day of May, in the year 1900, its operation and effect is suspended for 1 year from the 1st day of May, in the year 1906.
Md. Code, TP § 14-852