香港外來引種植物 （exotic species） 最常見的兩種是台灣相思和紅膠木。 紅膠木原產澳洲，葉墨緑，邊緣平滑，幼苗時，葉對生，長大後變為互生，樹葉於分枝頂聚生近似輪狀。白花，雄蕊如白色羽毛，細小不起眼，果成鐘形，蒴果 （capsule）。

The Taiwan Acacia and Brisbane Box can be counted as two of the most common exotic trees in Hong Kong.  Native to Australia, it has dark green leaves with smooth edges; opposite when young, alternate when mature, they rotate and aggregate on branch tops.  White flowers with numerous inconspicuous stamens appear in 5 feather-like bunches in summer.  Fruits are born in autumn as bell-shaped woody capsules that can be 2 cm large.