Violet fungus

Violet fungus is a type of fungus that grows up to 7' (2.1m) high.

Cormanthor
Cormanthor violet fungus grows only to around 3' (0.9m) high. It is often used by treants who will surround their roots with up to six of these fungi. The fungi's roots tap into the treant for sustenance and they help to protect it against bark-eaters by flailing with tentacles, attempting to rot the predator's flesh.