Bubbleaf

Bubbleaf is a plant solely made for Aquatic Castle. It makes air bubbles so you can plant your plants in the air bubbles. Without this plant, it would be impossible to plant anything in Aquatic Castle, making it a crucial plant in Aquatic Castle. Outside of that, it adds 1nd to any plant inside it. It is essentially useless in any other scenario.

Suburban Almanac Entry
Bubbleaf keeps making bubbles, Lily Pad keeps chillin' on the water, Flower Pot keeps bragging that he's considered a plant. "I don't get that last one." would be Bubbleaf's reply to Flower Pot bragging in that sentence.

Plant Food
The bubble slowly goes through each colour of the rainbow (including pink), and makes the plant inside it 2.5x faster.

Strategies
Simply use them to plant your plants in Aquatic Castle.

Trivia

 * Bubbleaf is a portmanteau of Bubble and Leaf.
 * It is unusable in any other world than Aquatic Castle.