Bird's-Nest Fungus

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Wayne's Word Noteworthy Plant For June 1996

Bird's-Nest Fungus

A Minute Fungus With A Remarkable
Method Of Dispersing Its Spores

This issue of "Noteworthy Plants" is dedicated to a tiny cup-shaped fungus containing minute flattened spheres resembling eggs in a bird's nest. It is the reproductive or fruiting body of a remarkable fungus known in scientific circles as Cyathus olla.

This unusual species belongs to the order Nidulariales (Class Basidiomycetes), a fascinating group of fungi appropriately named "bird-nest fungi." The little cups are about five millimeters in diameter, about half the size of an ordinary thumb tack. They appear during the late winter and early spring rainy season along a trail on the hillside east of the main Palomar College campus. The trail starts at a lovely creek lined with white alders and ascends a north-facing slope of dense coastal sage scrub where it connects with the upper part of the Palomar College Arboretum. Like the chaparral, this endangered California plant community receives its rainfall during the winter and spring, primarily in the months of January through April. The little cups only appear during this season when the soil is damp, particularly in shady places along the trail. They are not conspicuous and are easily overlooked by joggers and casual observers. This is yet another example of an inconspicuous species that lives out its life in a marvelous and unique cycle that is seldom seen by people.

Several fruiting bodies (splash cups) of the amazing bird's-nest fungus (Cyathus olla) growing along a trail through the Coastal Sage Scrub northeast of the Palomar College campus. The small size of these fungi (not their value) is indicated by the U.S. penny (one cent).

  How Large Is Penny In Above Image  

The cup-shaped fruiting body of Cyathus olla contains 4-5 or more "eggs." The eggs are flattened lentil-shaped structures called peridioles and they contain special cells called basidiospores by which this fungus reproduces and disperses itself. Each peridiole is attached to the inner surface of the cup by a slender, hollow stalk which contains an inner, coiled, threadlike, funicular cord. The fragile outer layer of the stalk (called the purse) is easily ruptured, thus releasing the inner, coiled, funicular cord. When wet, the funicular cord elongates greatly and may reach a length of 6-8 inches (15-20 cm). The base of this elongated cord (called the hapteron) is very sticky and adheres readily to solid objects after it is released from the cup.

Bird's-nest fungus (Cyathus olla). This specimen was growing in a flower pot with Brodiaea terrestris ssp kernensis collected from the Laguna Mountains of San Diego County.

Bird's-nest fungus (Cyathus olla) on the campus of Palomar College.

See Illustration Of The Remarkable Bird's-Nest Fungus

Cups of Cyathus essentially serve as "splash-cups" during a rain storm. Similar splash cups containing small asexual "buds" called gemmae are also found on the thallus of certain liverworts such as species of Marchantia. Rain drops falling at approximately six meters per second strike the cup and eject the peridioles to a distance of three to four feet. [In the related genus Sphaerobolus, the single peridiole in each cup is forcibly ejected by an internal osmotic pressure build-up, like a miniature cannonball shot from a funnel-shaped blunderbuss muzzle.] Even though it is only rain drops falling on the cup of Cyathus, the force of the ejection causes the fragile outer portion of the stalk (called the purse) to burst--thus releasing the inner funicular cord and basal hapteron that were coiled up inside the hollow stalk. Like a wad of glue, the sticky hapteron strikes a solid object, such as a nearby plant, adheres to a branch, and as the peridiole continues in flight the funicular cord expands to its full length. Then, like a tetherball winding around a pole, the peridiole winds around the branch where the hapteron has become attached. Thus, the peridiole soon hangs down vertically or is wound around the object to which the hapteron is attached. Upon drying, the peridiole splits open releasing its precious cargo of spores which fall to the ground--perhaps being carried by the wind to new substrates.

What is truly remarkable about this little fungus is the very specialized and elaborate method of dispersing its spores. It literally flings its peridioles up into a nearby shrub so the spores can be released into the air several feet above the ground. For more information see the fascinating article by H.J. Brodie (1951): "The Splash-Cup Dispersal Mechanism In Plants," Canadian Journal of Botany Vol. 29: 224-234.

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