Part of a 14-volume flora produced by the National Parks Board Singapore, volume 13 covers only one order of plants – the Gentianales. The order has five families: Rubiaceae, Gentianaceae, Loganiaceae, Gelsemiaceae and Apocynaceae. The Loganiaceae and Gelsemiaceae are more or less exclusively tropical and subtropical; the Rubiaceae and Apocynaceae are primarily tropical and subtropical but have small numbers of species in temperate regions; and the Gentianaceae is most diverse in the tropics but also has very large numbers of species in the temperate-alpine regions. In Singapore, they are primarily woody plants and range from subshrubs and epiphytes to large lianas and emergent trees. Globally, the Gentianales has about 1110 genera and about 20,725 species. In Singapore, where all five families are present, there are 93 genera, of which 5 are known only from introduced species, and 253 species, of which 15 are casual or naturalised introduced species. At 6% of the total, this is a fairly low percentage of introduced species compared to many other orders. The Flora of Singapore aims to describe the more than 3,000 native, naturalised and casual species of plants in Singapore. Botanists have been collecting and studying the plant diversity of Singapore for over 200 years, but never before has there been a comprehensive consolidation of all major plants groups only for Singapore. As of now, over 100 experts have committed to contribute to the project, more than half of which are based outside of Singapore. With the rigorous approach taken to ensure taxonomic and nomenclatural accuracy, the Flora of Singapore will be of interest to anybody studying the plant diversity of Singapore