Pikpik carrot
Pikpik carrots are vegetables native to Captain Olimar's home planet, Hocotate. In Pikmin, it is stated that Olimar's favorite soup contains "three large onions and hundreds of miniature red, yellow, and blue carrots". The reason Pikmin have their name is because Olimar believes that Pikmin resemble them, and they live in craft that resemble onions, which also reminds him of his favorite soup.
In Pikmin 2, pikpik carrots are seen in the in-game Piklopedia and look just like normal carrots - orange, about the size of a Pikmin, and having long leafy parts. These can be thrown at the Piklopedia's enemies and plants to see their reactions, such as the creature moving or waking up, or eating and attacking the carrots. The creatures will usually treat the carrots like Pikmin.
Golden pikpik carrots
Golden pikpik carrots are completely golden, even the leafy stem. They are a bit longer than the orange variety, and have three curled roots, instead of the basic cone-shaped root. These are thought to be very valuable, and, at the beginning of Pikmin 2, Louie is instructed to deliver a cargo of them. However, Louie encountered a "ravenous space bunny" which supposedly ate the whole shipment.