Morphological and molecular data show 'Synostemon trachyspermus' (Phyllanthaceae, Phyllantheae) to be a heterogeneous species assemblage

'Synostemon trachyspermus' (F.Muell.) I.Telford & Pruesapan (Phyllanthaceae, Phyllantheae) is shown, by morphological studies and phylogenetic analysis using nrITS DNA sequence data, to be a heterogeneous species assemblage of four species. 'Phyllanthus rhytidospermus' F.Muell. ex Müll.Arg., with a new combination provided as 'Synostemon rhytidospermus' (F.Muell. ex Müll.Arg.) I.Telford & Pruesapan, and 'Sauropus hubbardii' Airy Shaw, with a new combination as 'Synostemon hubbardii' (Airy Shaw) I.Telford & Pruesapan, are re-instated as species. 'Phyllanthus arnhemicus' S.Moore is lectotypified and placed in synonomy under 'Synostemon lissocarpus' (S.Moore) I.Telford & Pruesapan, which is the new combination provided for 'Phyllanthus lissocarpus' S.Moore (syn. 'Sauropus lissocarpus' (S.Moore) Airy Shaw). 'Synostemon umbrosus' I.Telford & J.J.Bruhl, a rare endemic from the Kimberley, Western Australia, is named as new. The newly described S. hamersleyensis I.Telford & Naaykens, endemic to the Pilbara, Western Australia, and the north-eastern Queensland endemic 'Sauropus aphyllus' J.T.Hunter & J.J.Bruhl are shown to be closely related; the new combination 'Synostemon aphyllus' (J.T.Hunter & J.J.Bruhl) I.Telford & Pruesapan is provided for the latter. 'Sauropus sp.' A of 'Flora of the Kimberley Region', previously included within 'S. trachyspermus sens.lat.', shows a more distant relationship and is named as 'Synostemon judithae' I.Telford & J.J.Bruhl. Notes on distribution, habitat, phenology, conservation status, photomicrographs of seeds and a key to identification of the species are provided.