Minecraft wiki entry for Development_versions, associated text: Birch forest
A forest made of birch trees.
Cold beach
A variant of normal beaches which generates when a snowy biome borders an ocean.
Deep ocean
An ocean biome variant, about twice as deep as it.
Can reach a maximum depth of the Y-coordinate in the low 20s.
The floor is covered with gravel.
Extreme hills+
A variant of extreme hills which contains spruce trees.
Flower forest
A variant of forest biomes.
Contains every flower in the game, except for sunflowers and blue orchids.
Gravel beaches
Consists primarily of gravel.
Ice plains spikes
Contains giant spikes made of packed ice, shaped similarly to upside down icicles.
Mega taiga
Contains 2×2 spruce trees,
Much of what is typically grass blocks in most biomes is replaced by podzol.
Contains grassless dirt.
Contains scattered "boulders" made up of moss stone.
Allows the generation of dead bushes, mushrooms, and ferns.
Mesa
Composed primarily of hardened clay in multiple colors and red sand.
Generates dead bushes.
Roofed forest
Has dark grass, giant mushrooms, and 2x2 dark oak trees.
Has extremely dense trees and leaves, sometimes dark enough for monsters to spawn during the daytime.
This is the first biome aside from the mushroom island that naturally spawns with huge mushrooms.
Savanna
Generates curved acacia trees.
Savannas are one of the two biomes where horses now spawn naturally, the other being plains.
NPC Villages may generate in savanna biomes.
Stone beach
Consists primarily of stone.
Composed of hills which are steep but not completely vertical.
Sunflower plains
Exactly the same as plains, but with the ability to spawn sunflowers.
Taiga
A non-snowy taiga variant.
The old taiga biome is now called cold taiga.