Molecular phylogeny, taxonomy and biogeography of Malaccotristicha australis comb. nov (syn. Tristicha australis) (Podostemaceae)

The systematic relationship of Tristicha australis C. Cusset & G. Cusset in northern Australia was investigated by comparative morphology and molecular phylogeny. Both lines of evidence show that it is most closely related to Malaccotristicha malayana (J. Dransf. & Whitmore) C. Cusset & G. Cusset and distinct from Tristicha trifaria (Bory ex Willd.) Sprengel and consequently the nomenclatural combination of Malaccotristicha australis is made. It is suggested that M. australis rapidly gained its characteristic morphology that is distinct from Malaccotristicha and resembles Tristicha. Phylogeographically, Australian Podostemaceae with two species, M. australis and Cladopus queenslandicus (Domin) C. D. K. Cook & Rutishauser, are probably derived, compared with the tropical Asian sisters. A key is provided to the species of Tristichoideae to distinguish M. australis and the other species.