Alphitonia is a genus of arborescent flowering plants comprising about 20 species, constituting part of the buckthorn family (Rhamnaceae) of the rosid eudicots. They occur in tropical regions of Southeast Asia, Oceania and Polynesia. These are large trees or shrubs. In Australia, they are often called "ash trees" or "sarsaparilla trees". This is rather misleading however; among the flowering plants, Alphitonia is not closely related to the true ash trees (Fraxinus of the asterids), and barely at all to the monocot sarsaparilla vines (Smilax).