Sweeney's Weed

Sweeney's Weed appears to be a large clump of black grass, with extremely long thick black roots covered in tendrils of white hair-like strands. It pulls moisture and nutrients from whatever soil it's buried in and prefers extremely wet environments, such as swamps or clay soaking pits.

It is known to the elves of the north as something to eradicate before settling an area. A master herbalist could use it as a biological weapon to weaken the building materials and economy of an area.