Giant Glowing Mushroom

Giant glowing mushrooms are destructible fungi that can be cut down with an axe like trees; however, they do not yield Wood, but Glowing Mushrooms and Mushroom Grass Seeds. Giant glowing mushrooms also give off light, like mushroom grass and glowing mushrooms do.

They have similar requirements as trees to grow: Additionally, the tiles with glowing grass must be low enough for the caps of the giant mushrooms to be under under Level depth, that is at least 16 tiles (32 feet) below. (No longer required as of patch 1.2)
 * The ceiling must be at least 15 tiles above the floor.
 * There must be no wall right on top of the floor for them to spawn, but there can be wall behind the floor and from 1 tile above it.
 * They will grow only when there's a flat patch of 5 blocks.
 * They will grow at least 2 tiles from each other.

When above ground, Giant Glowing Mushrooms are more tree-like, having branches of smaller mushrooms.