Gallows-Weed
From Tolkien Gateway
In the swamplands of Middle-earth was where the evil phantoms called Mewlips lurked, and the Gorcrows, a race of birds, flew. In these swamps also grew the Gallows-Weed. In Hobbit Lore, this tree-hanging weed is only known by name, but its physical description is never talked about or described. Few people who ever entered these marshes, and thus even saw these Gallows-Weeds, ever returned, thus there was no description of them.