Spindle headed Gall

Description:

All these galls were seen on the one tree and were cylindrical and about 6 to 7 mm tall. Some of them were gnarly with an opening which appeared to have a collar. Two other galls were smoother with small openings and smooth surrounds.
The galls appeared near the midrib of the leaf.

Habitat:

Seen on a peppermint gum in a national park.

Notes:

Going by Martin Lagerwey's spotting https://www.projectnoah.org/spottings/18... which suggests that these are parasitised female galls.
Male galls grow on their mother and appear as a compound gall contained in a cupula, an inverted dome shaped structure as seen in Martin's spotting.
The female has small spines on its head and hence the name spinifer.
My thanks to Penelope Mills for confirming the ID of the gall and host.