Plum tea origin and production site It refers to a tea made of plum, plum syrup, and omae (a medicinal herb made of undercooked blue plum mixed with smoke). It is usually made by mixing plum syrup in hot or cold water. Plum trees are a type of rose tree in the family Roses, also known as plum trees. Plums, which are fruits, are round in shape and ripen between June and July. Green plums harveste..