Calomnion complanatum is a species of moss native to Australia (New South Wales, Victoria, Tasmania) and New Zealand.

It is the type species of the genus Calomnion, growing on the trunks of tree ferns.

It is a small, yellow-green plant rarely more than 10 mm tall.

[3][4][5] Within New South Wales, Calomnion complanatum is an endangered species reported from only 4 populations, all in New South Wales: Cambewarra Mountain, Rocky Creek Canyon on the Newnes Plateau, and two sites on Mount Wilson (Zircon Creek and Waterfall Reserve).

This Bryidae-related article is a stub.