Md. Code, Real Property § 8-109

Uninterrupted possession for 12 months after the expiration of the lease containing a covenant for perpetual renewal of all or part of the leased premises by the tenant or any person claiming under the tenant operates as a renewal with respect to the entire premises. It conclusively is presumed in reference to the whole or any part of the leased premises, of which possession is retained, and in favor of the tenant or of the person claiming under the tenant, that a new lease of the whole of the leased premises was executed prior to the expiration of the lease by the landlord named in it, or by the person rightfully claiming under the landlord, to the tenant, or the person rightfully claiming under the tenant for the additional term under the rent and on the covenants, conditions, and stipulations as were provided in the lease.