From the Super Mario Wiki, the Mario encyclopedia
Chuckola Fruit is the main ingredient of Chuckola Cola. They only grow in the Chucklehuck Woods. Chuckola Fruit are oblong-shaped and have eyes and a mouth; their facial expressions can actually move and they can swing around on their branches, suggesting that they are sentient. There are three main types of Chuckola Fruit, each with their own unique flavor: Red Chuckola Fruit have a robust flavor, Purple Chuckola Fruit have a refreshing flavor, and White Chuckola Fruit have a tangy flavor. A fourth orange variety can be seen on trees, though nothing is known about them. Sometimes, the orange variety might actually be a Pestnut in disguise. To create the Cola from these berries, they must be drenched in syrup and told jokes (the quality of both the jokes and fruit affect the final product).
In Mario & Luigi: Superstar Saga and its remake, Mario & Luigi: Superstar Saga + Bowser's Minions, Mario and Luigi need to find the three kinds of Chuckola Fruit and bring them to Chuckleroot in order to proceed.
Names in other languages
Red Chuckola Fruit
White Chuckola Fruit
Purple Chuckola Fruit