Michael, I think that in the Richardson etal. Weeds of the south east book you will find this in the Brassicaceae as either Nasturtium officinale or Nasturtium microphyllum. On this site, these are in the genus Rorippa. I've also got some images of this genus but one needs more mature seed pods (for length and number of ssed rows) to take them to species, at least according to PlantNET
Hi Ken. Thanks for these notes. On my daily walk to-day I revisited and collected some plant material. I have recorded another sighting with seed pods. See- http://canberranaturemap.org/Community/Sightings/Details/1974216