Md. Code, Real Prop. § 14-609

(a) If the name of a person required to be named as a defendant is not known to the plaintiff, the plaintiff shall state in the complaint that the name is unknown and shall name as parties all persons unknown in the manner provided in § 14–613 of this subtitle. (b) (1) If the claim or the share or quantity of the claim of a person required to be named as a defendant is unknown, uncertain, or contingent, the plaintiff shall state those facts in the complaint. (2) If the lack of knowledge, uncertainty, or contingency is caused by a transfer to an unborn or unascertained person or class member, or by a transfer in the form of a contingent remainder, vested remainder subject to defeasance, executory interest, or similar disposition, the plaintiff shall also state in the complaint, so far as is known to the plaintiff, the name, age, and legal disability, if any, of the person in being who would be entitled to the claim had the contingency on which the claim depends occurred before the commencement of the action.