The status of two putative new species of 'Wahlenbergia' sympatric on the New England Tableland escarpment was investigated with morphometric analyses of a database derived from vegetative, floral and fruit characters and scanning electron microscopic studies of seeds. The following new species are described: 'W. rupicola' G.T.Plunkett & J.J.Bruhl and 'W. telfordii' G.T.Plunkett & J.J.Bruhl. Their distributions, habitats and conservation status are noted.

Phylogenetic analysis using an expanded data set of nrDNA ITS and PHYC and cpDNA accD and trns sequence data retrieves a monophyletic 'Synostemon' F.Muell. ('Phyllanthaceae, Phyllantheae, Flueggineae'), previously subsumed into 'Sauropus' Blume or 'Phyllanthus L. Sauropus s. str.', excluding 'Synostemon', is shown to be nested within 'Breynia' J.R.Forst. & G.Forst. (Chapter 2). Morphological data clarifies infrageneric relationships within 'Sauropus' and its species are transferred to 'Breynia' in a new subgenus, 'B. subgenus Sauropus' (Blume) Welzen & Pruesapan (Chapter 3). 'Synostemon hamersleyensis' I.Telford & Naaykens, a recently discovered new species endemic to ironstone detrital formations of the Hamersley Range in the Pilbara, central Western Australia, is named, its distribution, habitat and contentious conservation status discussed (Chapter 4).

Radical changes to concepts of relationships in Cucurbitaceae previously based on morphology have been made through phylogenetic analyses using multigene datasets. The Australian representation of 'Cucurbitaceae' tribe 'Benincaseae' is now considered to consist of eight indigenous genera including 'Muellerargia' Cogn., 'Zehneria' Endl. and 'Cucumis' L. from the subsumed tribe 'Melothrieae'. A phenetic analysis of 'Zehneria' using PATN has shown the genus in Australia to consist of at least two species, 'Z. cunninghamii' F.Muell. and an unnamed species previously referred to 'Z. mucronata' (Blume) Miq. Results were equivocal on the conspecificity of 'Z . baueriana' Endl. and 'Z. mucronata'. Phylogenetic analysis using PAUP was conducted on a molecular dataset from nuclear and plastid sequences of 75 taxa. Results indicated a new genus 'Austrobryonia' H.Schaef. must be segregated from 'Cucumis' ('Mukia') and is the closest living relative of the Eurasian and Mediterranean 'Bryonia' L. and 'Ecballium' L. of tribe 'Bryonieae'. 'Austrobryonia micrantha' (F.Muell.) I.Telford, 'A. argillicola' I.Telford, 'A. pilbarensis' I.Telford and 'A. centralis' I.Telford are endemic to inland Australia.