Biome/Before Beta 1.8

Biomes were introduced in Alpha 1.2.0, also known as the Halloween Update. The terrain generator and Biomes generator were majorily changed again in the Adventure Update.

Prior to the Halloween Update, a map had either a Snowy or Grassy theme that the player could choose between when creating the world. After the update, a world includes all biome themes generated in a distribution range that is determined from the biomes graph.

There were 13 biome types in 1.7: 10 in the Overworld, 1 in the Nether, and 2 unused ones that are in the code but aren't encountered in normal play.

The triangular-looking fern (also known as "living shrub") was rare, and only found in Swamp and Rain Forest biomes pre-1.8. At present, since Swamp biomes have been redesigned and renamed to Swampland, and Rain Forest removed entirely, "living shrubs" no longer generate naturally.

World saves from before the Halloween and Adventure Updates
Worlds generated prior to the update remained unchanged except for changes in grass color. This "biome" is known as Shrubland. However, any new chunks generated (by the player moving outside of the pre-biome world's generated bounds) do generate biomes, similar to the Nether being generated when you first enter it from a portal. Moving from 1.7.3 or earlier to 1.8 or later, the previous generated terrain stays the same but is in a different 1.8 biome. This is shown by the grass and leaf colors. A 1.7.3 forest biome could have the grass and leaf colors of a desert biome.

Taiga and Tundra biomes in 1.8
In 1.8, Notch said the Taiga and Tundra biomes would be left out until 1.9 because of problems in the biome generation code, but it only concerns the snow weather and snow layers as the other common features of this type of land can still be generated.

Pre-1.8 Biome Screenshots
The below screenshots were made by editing code in Minecraft's java files and creating worlds made of only one Biome. This was done consecutively with each Biome type and screenshots of each world are collated here. The original topic is on the Minecraft forum, here.