Blackvein

Blackvein is a large treelike plant that grows underground. It protrudes from soil-rich portions of cavern walls in large, black, veinlike bundles that continue to grow until uprooted. They are highly flammable, which proves dangerous once they reach considerable size, especially when nearby lava flow.

Dwarves regard them as beautiful, and thus do not often remove them completely. Many dwarves make a career out of trimming and caring for their kingdom's blackvein.