Domain — {3}{G}: Until end of turn, Sunbathing Rootwalla gets +1/+1 for each basic land type among lands you control. Activate only once each turn.
Domain abilities count the number of basic land types among lands you control, not how many lands you control or how many of any type.
The basic land types are Plains, Island, Swamp, Mountain, and Forest. Land types other than basic land types (such as Desert) don’t contribute to domain abilities.