There are many fungi in several genera called bird’s nest fungi because of the resemblance of their fruiting bodies to a tiny nest filled with eggs. One of the most common in Wisconsin is Cyathus striatus, the fluted bird’s nest fungus. This species is widespread throughout temperate regions of the world, developing on dead wood in open forests, typically growing individually or in clusters on small twigs and fallen branches or other wood debris. Because it also grows readily in bark or wood mulch, it is frequently found in landscaped yards and gardens. Other species grow on plant remains or cow or horse dung.
C. striatus, and others, are most commonly seen in the autumn when damp conditions promote their development, but they can be seen anytime conditions are appropriate. Even though each individual is small and inconspicuous, this species often grows in huge clusters, making them more noticeable – although they blend in so well with their background that it is very easy to overlook them.
All of the bird’s nest fungi look like miniature nests (generally only ¼ inch in diameter) filled with four or five tiny eggs. The cup-shaped “nest”, called a peridium, may be brown, gray or white, and smooth or textured inside and out. The “eggs” are actually disc-shaped bodies called peridioles that contain basidiospores.
C. striatus has rough, shaggy or hairy exterior and smooth but grooved inner cup walls, features that easily distinguished it from other similar bird’s nest fungi. This species varies somewhat in size and in color from a bright orange-brown to dark grey or dull brown, darkening with age. The peridioles vary in color from gray white through various shades of brown to almost black. The vase or cone shape of the nest part of the fruiting body allows for a splash-cup mechanism of dispersal of the spores when the “eggs” (peridioles) are hit by raindrops. The downward force of the drop hitting the interior of the cup ejects the peridioles into the air. The peridioles can be propelled up to 3 feet away, and stick to whatever they land on. After a while the periodioles split open to release the fungal spores.Small animals can also eat the spore-filled peridioles to disperse the spores after they pass through the digestive tract. In most situations the peridioles are unlikely to be noticed, but if lots of the “eggs” stick to the siding on a house or exterior of a vehicle they can be a nuisance as they are difficult to remove. You can try to manage the number of fruiting bodies by keeping conditions drier (good luck when it rains a lot) and raking mulched areas to disturb their growth. Growing a living ground cover will help, as well.
If the basidiospores released from the peridioles land on suitable wood or bark, generally in damp and shady spots, they germinate and produce new mycelium that infiltrates the wood or bark. Eventually when conditions are appropriate, that mycelium grows into new fruiting bodies. The immature nests are covered by a thin membrane called an epiphragm. Eventually this lid degrades once the peridioles are ripe, opening up the cup to expose the “eggs”, so that rain can splash them out to continue the cycle. The cups are very tough and persistent, so remain in the environment well after the “eggs” are splashed away.
– Susan Mahr, University of Wisconsin – Madison
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