Section 11. Taxes on real estate shall be assessed, in the town where it lies, to the person who is the owner on January 1, and the person appearing of record, in the records of the county, or of the district, if such county is divided into districts, where the estate lies, as owner on January 1, even though deceased, shall be held to be the true owner thereof; provided, that whenever the assessors deem it proper, they may assess taxes upon real estate to the person who is in possession thereof on January 1, and such person shall thereupon be held to be the true owner thereof for the purposes of this section; provided, further, that whenever the assessors deem it proper, they may assess taxes upon any present interest in real estate to the owner of such interest on January 1; and provided, further, that in cluster developments or planned unit developments, as defined in section 9 of chapter 40A, the assessment of taxes on the common land, so called, including cluster development common land held under a conservation restriction pursuant to section 31 of chapter 184, the beneficial interest in which is owned by the owners of lots or residential units within the plot, may be included as an additional assessment to each individual lot owner in the cluster development. Real estate held by a religious society as a ministerial fund shall be assessed to its treasurer in the town where the land lies. Buildings erected on land leased by the commonwealth under section twenty-six of chapter seventy-five shall be assessed to the lessees, or their assignees, at the value of said buildings. Except as provided in the three following sections, mortgagors of real estate shall for the purpose of taxation be deemed the owners until the mortgagee takes possession, after which the mortgagee shall be deemed the owner.

Whenever the assessors of any town assess a tax on real estate to a person other than the person appearing of record, in the records of the county, or of the district, if such county is divided into districts, where the estate lies, as owner on January first, such assessors shall, if the tax is a lien upon such real estate under section thirty-seven of chapter sixty, unless the assessors by reasonable diligence cannot ascertain the name of the person so appearing of record, include in such assessment the name of the person so appearing of record without imposing upon him personal liability for the tax.

Whenever assessors cannot by reasonable diligence ascertain the name of the person appearing of record, the assessors may assess taxes upon real property to persons unknown.

Real estate permanently restricted under section seventeen B of chapter twenty-one, section one hundred and five of chapter one hundred and thirty and section forty A of chapter one hundred and thirty-one shall be assessed as a separate parcel of real estate and real estate under a conservation restriction in perpetuity under section thirty-one of chapter one hundred and eighty-four subject to a written agreement with a city or town shall be assessed as a separate parcel and the city or town acting through its assessor shall be bound by the terms of the written agreement until its expiration. The initial assessment as a separate parcel shall be made on January first of the year next following the conveyance of such permanent restriction.