Relict floras of Atlantic islands: patterns assessed

St. Helena (South Atlantic Ocean) and Macaronesia have endemic plants that have been interpreted as relicts. This paper divides these relicts into three main types. It is suggested that type 1 relicts are of Miocene age. They are usually wet tropical forest trees, geographically and taxonomically highly disjunct from their nearest relatives. Type 2 relicts are of Late Miocene or Pliocene age, usually trees of tropical or subtropical seasonally dry vegetation, often with trans-African disjunction, and moderate taxonomic isolation. Type 3 relicts are of Late Pliocene or Pleistocene age, usually herbs of arid zone or temperate vegetation, with little taxonomic or geographical disjunction from their nearest relatives. Relict theory is defined, with discussion of its explanatory power to account for patterns of endemism, and more generally, taxonomic and geographical patterns of biodiversity.