water tree

:  any of several chiefly tropical plants with fluids that may be used as an emergency source of drinking water: such as a :  a large Ceylonese pitcher plant (Nepenthes distillatoria) b :  an African woody vein (Tetracera potatoria) that yields abundant watery sap when a large stem is cut c :  any of several chiefly arborescent Australian plants (as of the family Proteaceae) that yield a watery sap when the bark or roots are cut; especially :  a needle wood (Hakea leucoptera) that stores water in its thickened roots