From the Super Mario Wiki
Piranha Grove is a jungle found in Yoshi's Island. It appears as Stage 4-3 in the game, Yoshi's Story. The jungle, as told by the game, is ruled by the giant Piranha "Stalks", which are Piranha Plants that are the size of a short skyscraper and act very much like trees. This is also the home of Piranha Sprouts and Piranha Pests, which are found in no other place in the world.
The Yoshis knew the woods, but they never seen a place like the jungle. For the first time, the Yoshis saw Piranha plants, the kings of this jungle. One plant could swallow the Yoshis whole, so they left the jungle in a hurry.
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