Rubble

Rubble is found in small piles, and its use is exactly the same as that of the nectar weed. When Pikmin pass over a stockpile of rubble, whether directed to by the leader in charge or not, they will begin attacking the pebbles, causing them to randomly give out pools of nectar, until all pebbles have been destroyed. Compared to nectar weed, rubble is fairly rarely encountered.

In Pikmin: Attack of the Breadbugs
Rubble is used in the same way as nectar weed, and is found in the Toxin, Marsh, Arctic, and Inferno Territories of the Land of Wonders. It can also be found occasionally in Dangerous Depths. An unlimited number of Pikmin can be set to work on rubble at once, and Captain Olimar can destroy rubble by punching it.