Fantastic Flora

In real life, plants are important in nature. They provide oxygen, pollen for bees, food for herbivores and they make your garden look nice.

However, fantasy/sci-fi writers like to create their own unique plants with bizarre appearances and properties. Some may be carnivorous, fast-growing, even sentient. Some may be explosive, springy or maybe fiery.

You get the idea. They're very strange plants. They may or may not be just magic. Usually found on alien planets or in other dimensions. If someone can control these things watch out.

Anime and Manga

 * In One Piece:
 * The IQ plants, which stimulate evolution in animals that eat it. Dr Indigo used them to create SIQ.
 * Some of Usopp's Pop Greens become very bizarre plants such as a bush that grows into a wolf and the bulb releases a 3 meter diameter shock wave.

Literature

 * The Voynich manuscript has many pictures of plants, none of which have been identified.
 * Clark Ashton Smith loved this trope. Many of his stories feature it prominently.

Western Animation

 * From My Little Pony Friendship Is Magic:
 * Poison Joke which causes humorous afflictions on those who come in contact with it.
 * Zap Apples which only grow during a lightning storm and are used to make Zap Apple Jam.