Calyptella capula

The fruitbody is cup-like, with the mouth facing downward. The cup may be up to 5 millimetres in diameter and is shorter than it is wide. It is white but may darken with age, even becoming blackish (according to the Redhead & Traquair, see the references). The cup may be directly attached to its substrate or via a very short stem (which may be positioned centrally on the cup's upper surface, or be off to one side). The inner surface of the cup is smooth and the outer surface is almost smooth (some very fine bristliness showing in a magnified view).

The references given below record this cosmopolitan species from a wide variety of dead plant material, both monocotyledonous and dicotyledonous.

Given their small size and thinness, the fruitbodies will dry out very easily. Hence, expect to find this species where there is high humidity. That does not mean that the species is confined to wet gullies or rainforests. Thick layers of twig litter, mats of dead grass clumps, etc can hold moisture and create humid micro-habitats, suitable for fungi such as this, in otherwise dry areas.     

Look-alikes

Calyptella  is a plausible genus if  you see such small, smooth, mouth-downward, stemless (or very short-stemmed), white cups. However, getting to species requires a microscopic look. One very helpful microscopic feature of Calyptella capula is that the 'bristles' on the outer surface are intricately branched or coralloid. I assume that such outgrowths trap moisture and so stop (or greatly slow down) the drying out of the fruitbodies.  

References

Cooke, W. B. (1962). The cyphellaceous fungi. A study in the Porotheleaceae (=Beihefte zur Sydowia, 4).

Redhead, S.A. & Traquair, J.A.  (1981). Calyptella capula. Fungi Canadenses, No. 202, National Mycological Herbarium, Biosystematics Research Institute, Ottawa, Ontario.