A hamadryad (; ) is a Greek mythological being that lives in trees. They are a particular type of dryad, which are a particular type of nymph. Hamadryads are born bonded to a certain tree. Some believe that hamadryads are the actual tree, while normal dryads are simply the entities, or spirits, of the trees. If the tree died, the hamadryad associated with it died as well. For that reason, dryads and the gods punished any mortals who harmed trees. The Deipnosophistae of Athenaeus lists eight hamadryads, the daughters of Oxylus and Hamadryas:

• Karya (walnut or hazelnut)
• Balanos (oak)
• Kraneia (dogwood)
• Morea (mulberry)
• Aigeiros (black poplar)
• Ptelea (elm)
• Ampelos (vines, especially Vitis)
• Syke (fig)

Their mother, Hamadryas, is immortalized in the name of two genera: that of the cracker butterfly, and that of the northernmost monkey in Asia Minor, the hamadryas baboon. The cracker butterfly is more arboreal than most butterflies, as it commonly camouflages itself on trees. It feeds on sap, rotting fruit and dung. The hamadryas baboon is one of the least arboreal monkeys, but was the most common monkey in Hellenic lands.