Abstract
Mezoneuron is a genus segregated from Caesalpinia s.l. There are five species of Mezoneuron in New Caledonia, all of which are endemic to this island group. Full descriptions of the species are provided here, together with an identification key, a composite illustration, and distribution maps. Preliminary conservation assessments have been produced using distribution data from herbarium specimens in combination with knowledge of habitats and threats. These reveal a level of threat to each species ranging from Vulnerable to Critically Endangered. Three new combinations are proposed.