The Nidulariaceae ('nidulus' - small nest) are a family of fungi in the order Agaricales. Commonly known as the bird's nest fungi, their fruiting bodies resemble tiny egg-filled birds' nests. As they are saprobic, feeding on decomposing organic matter, they are often seen growing on decaying wood and in soils enriched with wood chips or bark mulch; they have a widespread distribution in most ecological regions. The five genera within the family, namely, Crucibulum, Cyathus, Mycocalia, Nidula, and Nidularia, are distinguished from each other by differences in morphology and peridiole structure; more recently, phylogenetic analysis and comparison of DNA sequences is guiding new decisions in the taxonomic organization of this family.

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