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.
Internally, the game recognizes the carrots as being Pikmin – this is necessary in order for the Piklopedia's carrot feature to work properly. The inclusion of a configuration file setting to enable pikpik carrots as party members is however quite mysterious.
Appearance-wise, they float slightly above ground, and are animated in a fashion similar to those of regular Pikmin, except less articulated. Their stems always include a leaf, regardless of their maturity or the effects of an ultra-spicy spray. When idle, their stems glow green, much like Bulbmin. All of their sound effects match those of regular Pikmin, besides Bulbmin.
The code that shows the standby Pikmin type on the HUD ignores these type of Pikmin, so they lack an icon.