Abstract
The present study elucidates the phylogenetic relationship within the tribe Riedelieae in family Zin-giberaceae, with a main focus on the genus Pleuranthodium and its intrageneric relationship. Previ-ous phylogenetic studies have only included up to five species of Pleuranthodium and its neigh-bouring genus Riedelia. The present study utilises more regions of DNA than previously used, and a total of 73 collections from the tribe, including 53 samples of Pleuranthodium and 14 Riedelia. The morphological division of the genus Pleuranthodium by Schumann (1904) and Smith (1991) is test-ed with phylogenetic methods. The phylogenies were constructed using separate chloroplast and nuclear dataset and finally a combined dataset, all analysed with Bayesian Inference and maximum likelihood. Dating phylogenies were performed using the nuclear internal transcribed spacer (ITS) and calibration with fossil data and Siphonochilus as outgroup. The biogeographical distribution was explored using herbarium metadata from GBIF. The monophyly of Pleuranthodium is well supported, and the Riedelia grade is the sister group. The two sections within the genus, Pleu-ranthodium and Psychanthus, are also monophyletic with lower support. Morphologically, the two sections are easily distinguished, and good diagnostic characters are found for both. The genus sep-arated from its Bornean origin approximately 13 Ma, with subsequent radiation, mainly in New Guinea. Species on smaller islands to the east of New Guinea are younger.