Sunflower

Sunflowers are obtained by destroying the grass on the block under them with a pickaxe; they are also sold by the Dryad. You can plant these mainly just for decoration, but they can also stop corruption from spreading.

Sunflowers can only be placed on grass and hallowed grass. Placing them on corrupt grass and dirt will not work. Sunflowers are 2 blocks wide and 4 blocks tall. They cannot be planted in a plant pot. A sunflower may be planted anywhere, so long as the soil and space conditions are met. No background walls may be present where the sunflower is placed.

They are extremely useful for changing a corruption biome to a regular one. Use these if you want your world to be corrupt and still have NPCs without setting up a space station for them to live in.