Coral

Coral grows in the oceans at the ends of the world. It will grow on sand under water at least 5 tiles deep. Background walls block its growth. It also requires to be within 250 tiles of the edges of the map and above the depth of 0 feet. It can be picked up just like the Cactus, by either by hitting it with a Hammer or by mining out the block of Sand underneath it. Also placing a block next to it will make it drop.

It can be placed as a decoration, just like Books can. Once set, it can have one of many appearances (again, like Books) and is sometimes more than one block wide, so bear that in mind if you're trying to place other things next to it.