This unusual shrub belongs to the Acanthaceae family of plants, which has many shrubby members very suited to our Sydney climate. I obtained my plants at the local village fete many years ago and have never seen it anywhere again. It appears to be native to Thailand,China, India, Burma and Laos. It has little bell-shaped flowers of plain white or lavender with a deep purple throat, from summer to early autumn, and grows about 50 - 100cm tall. It has long narrow leaves. Other members of the genus are said to become weedy, but this one does not, apparently. Like many others in the Acanthaceae family, it will tolerate shade and dry conditions. I cut it back in late August and it is easily propagated from cuttings taken at that time. It looks scruffy in winter but will survive an average winter in Sydney.
The correct name for this plant is possibly Asystasia travancorica.