From the Super Mario Wiki
In the Wii game Mario Party 9, Z-Bananas are the DK's Jungle Ruins equivalent to Mini Ztars. Passing over one Z-Banana, or a pack of three will cause the player to lose 1 or 3 Bananas respectively. Z-Bananas are the same color as Mini Ztars as they are a dark purple. It is impossible to receive Z-Bananas in the Captain Event of DK's Jungle Ruins, and there are none in the Boss Minigames of the board.