Acorn Plains

Acorn Plains is the first world of New Super Mario Bros. U. It is a plains world with acorn trees, lots of shrubs, and jagged mountains reminiscent of some of the backgrounds in Super Mario World. This world has at least seven levels, a red and green Toad House, a Piranha Plant Enemy Course, and a spot where a magenta Baby Yoshi walks near. The Castle boss of this world is Lemmy Koopa. This world's most defining feature is the Acorn Tree, found in the game's intro, Acorn Plains' map, and said world's first level.

Trivia

 * In early builds of New Super Mario Bros. U, the Acorn Plains map looks substantially different. The Acorn Trees did not show the Super Acorns, the map had two red Toad Houses, and the green Toad House was in a different spot, there are two Enemy Courses instead of one, and the spot where the magenta Baby Yoshi was is gone.
 * There is a pipe at the beginning of the world. It could possibly be a way to get to later finished worlds easier, as Layer Cake Desert and Frosted Glacier has the same pipe at the beginning of the world.