Antirhea is a genus of the tribe Guettardeae of the flowering plant family Rubiaceae. It comprises frutescent to arboreus species having dioecious flowers arranged in basically dichasial cymes (frequently reduced to solitary flowers in pistillate plants), imbricate corollas with three to four lobes, and the same number of subsessile to sessile stamens. The ovaries have usually two to twelve locules, and the drupaceous fruits have fused pyrenes, and persistent calyces as well as flower bracts Thirty-seven species, including thirteen described as new, eleven new combinations and one variety are recognized from the Paleotropics. Three subgenera are proposed: Antirhea, Guettardella, and Mesocarpa. In the Old World, Antirhea extends from Madagascar and the Mascarene Islands eastward to the Malay Peninsula, Borneo, the Celebes, Moluccas, Lesser Sunda Island, New Guinea, tropical Australia, the Solomon Islands, New Caledonia, Fiji, and Samoa, with a northern extension to Southern China and the Philippines The study gives a taxonomic history of the genus concerned and a systematic analysis of the Old World species. It is based upon reproductive and vegetative structures, foliar venation patterns, petiolar anatomy, pollen morphology, and phytogeography. Cladistics analyses were undertaken in order to achieve preliminary notions as to the phylogenetic relationships of the genus and its infrageneric taxa
