Bulbasaur from Best Starter Pokemon
Bulbasaur has a "bulb" on its back that grows steadily larger as it matures. This bulb contains a seed which uses photosynthesis to supply Bulbasaur with energy. Its bulb is also used to store the energy that the seed absorbs, which can be used when it is necessary. It is assumed that when a Bulbasaur collects enough energy in its bulb, it will evolve into an Ivysaur.