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Cyathus is a genus of bird's nest fungi in the family Nidulariaceae, so named since they resemble tiny bird's nests filled with eggs. The "eggs", or peridioles, are attached to the inner surface of the fruiting body by a cord of mycelium. Both surfaces of the cup may be ridged longitudinally, a taxonomic characteristic that has traditionally served to distinguish between species. Cyathus species are widely distributed across the globe, and some are found in most countries, although a few are localized. C. stercoreus is considered endangered in a number of European countries. Generally considered inedible, Cyathus species are saprobic, obtaining nutrients from decomposing organic matter. They usually grow on decaying woody material, on cow and horse dung, or directly on humus-rich soil. The life cycle of this genus allows them to reproduce both sexually via meiosis, and asexually via spores. Phylogenetic analysis has provided insights into the relationships between the various species.