A peculiar stone that can make certain species of Pokémon evolve. It burns as red as the evening sun.
Special evolution items like the Sun Stone first arrived back with the second generation of Pokémon, and are now required when evolving Pokémon such as Sunflora and Bellossom and Bellossom and Whimsicott and Lilligant. When evolving these Pokémon, this item is required in addition to the candy, and is consumed when used.
How to evolve Sunkern into Sunflora
In order to evolve your Sunkern into Sunflora, you will need to have a Sun Stone with you in your bags. You will also need to have all 50 candy, in the same way as with a normal evolution.
On your Sunkern pokémon's screen, select the evolution through the usual in-game menu. The Sun Stone and candy will be consumed, and you'll have a new Sunflora with hopefully all the right moves.
In Pokémon GO, evolving Sunkern into Sunflora is a lot simpler than some of the other Pokémon games which required your Pokémon to also be traded to another player for the evolution to take place.
How to evolve Cottonee into Whimsicott
Evolving your Cottonee into Whimsicott works in the same way as with the other evolution above:
To evolve your Cottonee into Whimsicott, you will need to have a Sun Stone with you in your bags. You will also need to have all 50 candy, in the same way as with a normal evolution.
On your Cottonee pokémon's screen, select the evolution through the usual in-game menu. The Sun Stone and candy will be consumed, and you'll have a new Whimsicott.
How to evolve Petilil into Lilligant
Evolving your Petilil into Lilligant works in the same way as with the other evolution above:
To evolve your Petilil into Lilligant, you will need to have a Sun Stone with you in your bags. You will also need to have all 50 candy, in the same way as with a normal evolution.
On your Petilil pokémon's screen, select the evolution through the usual in-game menu. The Sun Stone and candy will be consumed, and you'll have a new Lilligant.
How to get the Sun Stone
The Sun Stone is obtained from spinning Pokestops and Gyms. There is a very low drop chance of around 1% per spin to receive a Sun Stone or any of the other evolution item, and there is an equal chance of obtaining each of the 5 currently available items.
There's no way to ensure that the Sun Stone will drop, but with only 4 other items, there's a greater than 50% chance that you'll receive one once you've spun over 250 Pokéstops.
The 7th day streak bonus gives you a very high chance of obtaining one of the evolution item, but it's not believed to be guaranteed.
Other evolution items
The other evolution items that can be found in Pokemon GO are: