Port Jackson willow or Port Jackson wattlen (Plants) an Australian acacia tree, Acacia cyanophylla, introduced in the 19th century into South Africa, where it is now regarded as a pestCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014