Flagellariaceae are grass relatives that climb using leaf-tip tendrils in palaeotropical rainforests. As the sister group to Joinvilleaceae, Ecdeiocoleaceae and Poaceae, they could be indicative of the ancestral habitat of the graminid clade. Although four species are usually accepted in this monogeneric family, Flagellaria has never been revised taxonomically and species delimitation is understood poorly, especially for the Pacific. Here, we document the morphological variation in the genus, and explore phylogenetic patterns by maximum likelihood analysis (GARLI) and Bayesian inference (MrBayes) of the internal transcribed spacer (ITS) of the nuclear ribosomal repeat and the plastid matK, psbA–trnH and rps16 regions. Ecological variation was inferred from climatic factors evaluated by MaxEnt analysis. We show that Flagellaria is more diverse than previously thought, and describe one new species in Fiji (Flagellaria collaris Wepfer & H.P.Linder) and three new varieties in F. indica (vars. australiensis, bifurcata, borneensis). Flagellaria is most diverse in the Pacific islands, where Fiji harbours three of the five species.