I recall seeing, on a trip to Rockhampton in about 1975, some stands of cactus that I took to be prickly pear. I was surprised to see it, as I had heard the story of the rampant infestation and the eventual control through Cactoblastis, so I thought it had been eliminated. A newsreel from the twenties gives some idea of the severity of the problem.
I had another prickly pear surprise not long ago. The train home from work goes from Southbank Station (once Vulture Street Station) under Vulture Street and into a long cutting. At the top of one of the embankments is Somerville House high school. Staring out of the window, I suddenly noticed a healthy clump of pear at the base of the embankments. I realised that there were smaller clumps of it growing all over the stone bank on that side. As suddenly as it had appeared, it was gone; even before the tunnel under Stephens Road I couldn't find any more of it among the angled planes of the wall.
So, is this a stable population, of has someone, not too long ago, tossed a fruit down the embankment? The next year should tell the tale.