Historical Rules · 7 August 2020
Rule 205.3i
Official source text from the 7 August 2020 Rules release
Lands have their own unique set of subtypes; these subtypes are called land types. The land types are Desert, Forest, Gate, Island, Lair, Locus, Mine, Mountain, Plains, Power-Plant, Swamp, Tower, and Urza’s. Of that list, Forest, Island, Mountain, Plains, and Swamp are the basic land types. See rule 305.6.