Purple Pikmin are a species of Pikmin found in Pikmin 2 and Pikmin 3. They are first found in the Emergence Cave. They have six hairs, used as feelers rooted in their heads.

These Pikmin are very strong due to their weight and are the most durable out of all Pikmin Types. They are specifically required to obtain a number of treasures, two of which are needed to gain access to new areas, making them necessary to complete the game. While it is possible to clear the debt in the first area, this takes a substantial amount of time to finish, as eventually the only form of income that remains are enemy corpses.

Purple Pikmin share a number of similarities with White Pikmin. They can only be obtained via certain Violet Candypop Buds and have magenta flowers rather than white. In addition, at the end of each day, they are stored in the ship; as opposed to an Onion. Purple Pikmin are the heaviest, slowest Pikmin species known, but are also the strongest.

In Pikmin 3, Purple Pikmin only appear in Mission Mode and Bingo Battle and are obtained the same way as in the previous game as well as pre-spawned sprouts. Their main purpose in this game is to be heavy lifters. Therefore, all of their abilities aside from being 10x stronger have been removed.

Source: http://pikmin.wikia.com/wiki/Purple_Pikmin