Phytolith occurrence in predominantly the leaves of 177 non-Poaceae plant species, representing 53 families, from northwest Australia were investigated with the aim of creating a comparative collection to assist interpretations of phytolith assemblages recovered from archaeological and geological contexts. Approximately 50% of the samples examined were found to be non-phytolith producers. The remaining samples produced variable quantities of phytoliths, ranging from minimal traces to abundant amounts. A range of phytolith morphologies was observed, including both distinctive and redundant forms. Comparison of the results from this study with those conducted in other geographical locations reveals a general continuity of patterns within families, thereby suggesting a high level of genetic control for phytolith production. However, differences between the results of this study with another major Australian study [Bowdery (1996) Unpubl. Ph.D. Thesis, Aust. Natl. Univ., Canberra, (1998) BAR Int. Monogr. Ser. 695, Hadrian, Oxford] seem to indicate that environmental factors must also be considered to play an important role in determining the nature of phytolith production. It is concluded that phytoliths constitute a valuable microfossil system for the reconstruction of palaeovegetation, palaeoclimate and plant–human interactions in the tropical region of northern Australia.