Used to think they are the fruit of the plants.Allocasuarina galls are initiated by females of Cylindrococcus spiniferus. Each gall( The gall is part of the foliage, stems and leaves),houses a single female. When fully mature, she mates with a male and gives birth within the gall which she never leaves. The nymphs leave the gall to a new branchlet to initiate their own gall.If you open the gall up, you will find a little fellow inside.

Bribie island national park.
Canon kissx3 ef 60mm f/2.8 USM