A plant is a type of item used to decorate bedrooms in the Generation II games and Secret Bases in the Generation III and IV games.
In the second generation of games, there are three plants available. All are obtained using Mystery Gift.
One feature of Pokémon Stadium 2 allows players to view the entire room and its decorations, including any plants, in 3-D.
In the third generation of games, there are six plants available. These can be bought at the Pretty Petal Flower Shop on Route 104.
In Generation IV, plants are purchased from Goods Merchants in the the Underground in trade for spheres.