A genus of plants of the Pulse family, including the catechu and gum-arabic trees. The species are numerous, are frequently thorny, and grow mostly in warm countries. Nearly 300 species are Australian or Polynesian and have vertically compressed leafstalks, instead of the bipinnate leaves of the much fewer species of Africa, etc. Very few are found in temperate climates, but many are cultivated in greenhouses for the sake of their flowers, which are of great beauty and often fragrant. The North American locust tree and other species of robinia are often called acacia in the United States and Europe, but wrongly.