Nardoo (scientific name Marsilea spp.) is a small freshwater fern, common across semi-arid and arid Australia. While reported as an important starchy food, albeit requiring complex processing in some regions, it is not well known as a food source in the Pilbara of Western Australia. Here we describe plant residues including megaspores, starch grains, cellulose, and fibres on a portable grinding stone from the surface of a rockshelter in the West Angelas region of the Central Pilbara. These residues display physical characteristics that strongly suggest they derive from nardoo. Given these findings, we encourage researchers to consider nardoo processing and consumption in future ethnobotanical and archaeological studies in the Pilbara.