Volume 5 contains four important tree families, viz. the Apocynaceae, Dipterocarpaceae, Symplocaceae and Thymelaeaceae, covering 373 species in 28 genera. Of the total number of species treated, 211 or about 56.6% are endemic in Borneo, 18 or about 4.8% in Sabah, 32 or about 8.6% in Sarawak, and 7 species are new to science. The account of the Dipterocarpaceae makes Volume 5 particularly significant; Dipterocarpaceae is the most structurally dominant tree family, as well as the principal source of commercial timbers from Borneo's natural forest. Volume 5 will be of special interest to ecologist and foresters alike. The information pertaining to conservation status of all known dipterocarp species occurring in Sabah and Sarawak will in some way contribute towards the conservation and better management of this economically important tree family. The project continues to improve the quality of this publication series. In this volume, some colour plates of the trees revised are included.