Carolyn, this plant also occurs on Red Hill, where it was introduced at least 30 years ago, probably in hay or the stomach or hides of cattle that Charlie Russel moved between Canberra and a property in Northern NSW. It gets hit pretty badly by frost but may be a beneficiary of climate change and if you only have 1 -3 plants i would eradicate them.
It has a short thick root and the stems can break off. I pulled or dug out 256 the other week but left a few roots so I will need to go back. At least it is a reduction from thousands last year.
Thanks Carolyn - Other than Black Mountain I don't think that there is anywhere in the region with as many significant sightings as your property, so great that you are keeping it in good nick