Sleeping-willows were trees found in the Deepwoods. It was similar to other willows, such as sedgewillows, waterwillows, weeping-willoaks, and woodwillows. When ground to a powder, sleeping-willow bark could be used as a sedative.
During the events of Midnight Over Sanctaphrax, whilst Twig Verginix and Cowlquape Pentephraxis were aboard Thunderbolt Vulpoon’s sky ship—on their journey to reunite with the other members of the Edgedancer—the ship’s treacherous captain attempted to knock out Twig and Cowlquape with woodgrog laced with powdered sleeping-willow bark. Thunderbolt Vulpoon had his servant, Grimlock, serve it, desiring to incapacitate his guests in order to easily enslave them. However, to the captain’s dismay, Twig caught on and dumped the goblets out a porthole of the Skyraider.