Towercap

Towercaps are giant mushrooms the size of Trees, and for most purposes function like them. They are cultivated in Treeplanter's Pots, and then planted in the ground. However, unlike normal trees, they must be planted in Caves and give no sticks, bark, or boughs.
Further, preliminary results indicate that they require 3x or more the growth time of other trees. This is likely due to Towercaps using the same growth time as other trees, but because caves do not count as forest biome, they will always grow at the speed that other trees do before they convert the biome beneath them to forest.