Dryad of the Ilysian Grove’s first ability is cumulative if you control more than one. It’s also cumulative with other effects that let you play additional lands, such as the one from Escape to the Wilds.

Each land you control will have the land types Plains, Island, Swamp, Mountain, and Forest. They’ll also have the mana ability of each basic land type (for example, Forests have “{T}: Add {G}.”). They’ll still have their other subtypes and abilities.

Giving a land additional basic land types doesn’t change its name or whether it’s legendary or basic.