There are a whole bunch. I'm pretty sure i won't be covering all of them, but anyways here are the ones i know of off the top of my head:
1: A leaf stone can be used on Gloom to evolve it into a Vileplume.
2: A leaf stone can be used on Weepinbell to evolve it into a Victorybell.
3: A leaf stone can be used on Paras to evolve it into a Parasect.
4: A leaf stone can be used on Exeggcute to evolve it into a Exeggutor.
And just to get this clear, Evee does not evolve into a leafeon with a leaf stone.
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The leaf stone will evolve certain species of pokemon
You get a leaf stone underground.
A leaf stone it will become vileplume.
Take a leaf stone and use it on him.
You have to use a leaf stone on your eevee. Sorry, I don't know where to find a leaf stone though. : ) hope this helped!