Although I am reasonably confident with my identification here, I am not 100% sure, so if any readers have informed opinions for or against the identification, I would be grateful to hear of them.
Plectania campylospora, Brown Forest Cup, from family Sarcostomataceae, is found on rotting wood in wet forests.
Fungimap Australia give the size of the 'cup' as "to 80mm wide and 60mm high", but the 6 specimens I have seen have been no more than 20mm wide and high.
Exterior surface of Brown Forest Cup is more black than brown, and has a roughened texture. The interior of the deep cup is smooth and brown, aging to black. The short stem is slightly rough in texture, and can be crinkled as shown in my photos here.
Rough exterior and short crinkly central stem
Although reportedly growing in groups, the specimens of Plectania campylospora that I have found have been growing singly. Its dark colouring and unobtrusive nature makes this cup fungus difficult to spot in the dim light of the rainforest, but it is always a pleasure to find.
Known Australian distribution appears to be south eastern coast and ranges, including Tasmania.
A shallower cup
[This will be updated with new sightings]
Barrington Tops National Park, NSW - on rotting twigs on the rainforest floor - Apr, May, Nov.
New England National Park, NSW - on rotting wood on floor of wet forest - May.
The cup fungus has pushed aside wood as it emerged