Note that no biome has all of these, and some, such as Mordor, have none.
Flowers - A version of [biome name] with an abundance of flowers.
Forest - A more forested version of [biome name].
Steppe - A very flat version of [biome name].
Barren Steppe - A steppe, but with no trees. Structures generate here very commonly.
Hills - A hillier version of [biome name].
Mountain - A mountain that rises from the surrounding terrain.
Dense Oak Forest - A forest of densely clustered oak trees.
Dead Oak Forest - A forest of dead oak trees.
Oak Shrubland - A version of [biome name] will short, shrublike trees.
Dense Spruce Forest - A forest of densely clustered spruce trees.
Dead Spruce Forest - A forest of dead spruce trees.
Light Forest - A lightly forested version of [biome name].
Dense Forest - A densely forested version of [biome name].
Dead Forest - A version of [biome name] forested with dead trees.
Dense Birch Forest - A forest of densely clustered birch trees.
Forest Clearing - A clearing in the surrounding forest.
Forest Hills - A forested version of the hill variant.
Swamp Upland - A version of the [biome name] with fewer pools, higher land generation, and many more trees.
Swamp Lowland - A variant of the [biome name] that is more or less flat, and is more like a vast pool choked with bits of land and quagmire.
Baobab Savannah - A variant of the Far Harad Savannah covered with a forest of Baobab trees.