I don't always eat bananas,
but when I do, they're from a Tropius.

From Tropius' entry on Ruby:
"The bunches of fruit around Tropius's neck are very popular with children. This Pokémon loves fruit, and eats it continuously. Apparently, its love for fruit resulted in its own outgrowth of fruit."
From Sapphire:
"Children of the southern tropics eat as snacks the fruit that grows in bunches around the neck of Tropius. This Pokémon flies by flapping the leaves on its back as if they were wings."
From Emerald:
"It flies by flapping its broad leaves. The bunch of fruit that grows around its neck is deliciously sweet. In the spring, it scatters pollen from its neck."
From FR/LG:
"It lives in tropical jungles. The bunch of fruit around its neck is delicious. The fruit grows twice a year."

Hail Bulbapedia.