Bisporella citrina (Yellow Fairy Cups or Lemon Discos)

The fruit body is uniformly yellow, opaque and saucer-like or disc-like (technically an apothecium). The apothecia are up to 3 millimetres in diameter and with or without a short stem.

The apothecia appear on wood, typically in large groups, growing closely or even abutting  (and then mutual pressure may distort the apothecial shape).

Look-alikes

The yellow apothecia of Bisporella sulfurina are up to 1.5 millimetres in diameter.

Gates & Ratkowsky (on page 216 of A Field Guide to Tasmanian Fungi, 2nd. ed.) note an un-named species that they call Bisporella 'green-yellow', with apothecia 3-5 mm, yellow to start with but later with a greenish hue.

The yellow Bisporella species noted above grow on wood. There are also small yellow apothecial fungi that grow on soil, dung, some seed cases or herbaceous plants.

Some species of Orbilia (stemless, small and yellow) appear on wood but the apothecia are glassy and semi-translucent (and microscopically distinct from Bisporella).

There are also small apothecial fungi, on wood, with a yellow upper surface to the apothecia but different on the underside.