A revision of Omalanthus (Euphorbiaceae) in Malesia

Omalanthus is revised for Malesia and the Solomon Islands. For this region, 13 species without subspecific taxa are accepted, namely O. arfakiensis, O. caloneurus, O. fastuosus, O. giganteus, O. grandifolius, O. longistylus, O. macradenius, O. nervosus, O. novoguineensis, O. populifolius, O. populneus, and O. trivalvis, and, as a new species, O. remotus. In addition to established synonyms, 17 species from Malesia are not accepted any more. The diagnostical importance of a peltate or non-peltate leaf base is especially doubted. Although detailed phylogenetic and biogeographical analyses were not made, the value of the established sections of Omalanthus is questioned. An alternative subdivision unites all Malesian taxa into four subgroups, each with a distinct distribution of probably historic causes. The subgroups are distributed in W and C Malesia, the Lesser Sunda Islands, the Philippines and the Bismarck Archipelago, and New Guinea and Australia, respectively. The radiation in montane and subalpine habitats may also have contributed to the actual diversity. In addition, O. gracilis from French Polynesia is proposed to be a synonym of O. stokesii.