Bisporella citrina

Scientific name: Bisporella citrina (Batsch : Fries) Korf &
Carpenter 
Derivation of name: Citrin- means "lemon-yellow."  
Synonyms:  Helotium citrinum; Calycella citrina
Common name(s):  Yellow fairy cups
Phylum:   Ascomycota
Order:   Helotiales
Family:   Helotiaceae
Occurrence on wood substrate: Saprobic; in clusters on
decaying wood; summer through fall.  
Dimensions: 1-3 mm wide    
Sterile outer surface:  Bright lemon-yellow to golden-
yellow; smooth; stalkless or with thick, stalk-like
base.        
Fertile inner surface: Same coloration as sterile surface;
smooth.
Edibility: Unknown
Comments: Although individually tiny, these fungi often
occur in such large numbers that they become quite
conspicuous.

More information at MushroomExpert.com:   


Figure 1. The bright yellow fruit bodies of Bisporella citrina
are very common on decaying wood.


Figure 2. The color of the fruit bodies ranges from
bright lemon-yellow to golden-yellow.
Photo © Larry Grand.


Figure 3. Bisporella citrina may have a rudimentary
stalk, as shown here, or it may be stalkless.

Figure 4. Yellow fairy cups typically occurs in groups or
dense clusters.

Figure 5. The fertile inner (upper) surface and outer surfaces
are the same color.


Figure 6. Another small cup fungus, Chlorosplenium chlora,
has a bright yellow outer surface but the fertile surface
becomes greenish at maturity. Bisporella citrina is on the
right and Chlorosplenium chlora is on the left.