I am beta testing my key to plants of SE NSW and tried it out on this assuming that the plant was 0.3-1 m high and has seed cases with prickles. It did not come out to anything sensible. This plant is not either Datura ferox nor Datura stramonium, the two species of Datura in the key. Nor anything else in the tomato family. This means that it is a plant not in my key. I deliberately left out rarer weeds to keep the number of species down to 3,000.
The patch of D. stramonium nearest to me has been mowed so I can't do a comparison. The seed pods are like Datura stramonium. The leaves look a bit stressed and a picture of some of the larger leaves on the plant would help.
Leaves and pod seem to match to Datura wrightii http://www.flora.sa.gov.au/efsa/lucid/Solanaceae/Solanaceae%20species/key/Australian%20Solanaceae%20species/Media/Html/Datura_wrightii.htm
The way the veins are arranged in the leaves is similar to the arrangement in Datura wrightii. However i am not sure this plant is hairy enough. In addition stalks of the seed cases of Datura wrightii curve down as it matures, which some of these do not appear to do. On the whole though I agree with Michael. So a specimen to the australian national herbarium or the botanic gardens?
Thanks Davob - Dature wrightiii has not been recorded before in the ACT so we are unfamiliar with exactly how it looks and it's sighting is of interest.