A total of 175 species of amenity trees, ranging from rare to common, have been identified in urban Hong Kong. Information on the geographical origin of these species is gleaned from a wide spectrum of botanical literature. About three quarters of the diverse tree population are exotics introduced from a selection of geographical regions. Tropical Asia is the most important contributor, followed by Australia, Tropical America and Far East, and the remainder from disparate and remote lands. The domination of aliens is especially pronounced in the palms and palm-likes and conifers, but less so for the broadleaved. The conditions conducive to tree introductions, both past and present, are explored. The need for active research and free exchange of relevant information in the tropics is advocated. Copyright © 1992 Taylor & Francis Group, LLC.