Exidia nucleata  (Schwein.) Burt - Crystal Brain Fungus

Phylum: Basidiomycota - Class: Tremellomycetes - Order: Auriculariales - Family: Auriculariaceae

Exidia nucleata, Crystal Brain

Exidia nucleata is a fairly common (at least in Britain and Ireland) species of jelly fungus; it appears on rotting hardwood, and particularly beech. In dry weather this fungus shrinks and becomes quite hard, so you really need wet weather to find this fungus: during dry spells it shrivels up almost completely to leave just a transparent rubbery patch on the host wood.

Autumn and winter are the best times to look for this jelly fungus.

Closeup picture of Exidia nucleata, Crystal Brain

Distribution

Exidia nucleata occurs throughout Britain and Ireland, but it is most commonly found in the south. This jelly fungus can be seen also in many countries on mainland Europe, in North America and and in northern Africa.

Taxonomic history

The basionym of this species was established in 1822 by American mycologist Lewis David von Schweinitz (1780 - 1834), who named it Tremella nucleata. Its widely-accepted scientific name Exidia nucleata dates from a 1921 publication by another American, Edward Angus Burt (1859 - 1939). Some authorities, particularly those in the USA, do not agree and place this jelly fungus in the genus Myxarium. Here I am following the Kew/British Mycological Society systematics.

Synonyms of Exidia nucleata are numerous and include Tremella nucleata Schwein., Naematelia nucleata (Schwein.) Fr., Myxarium nucleatum (Schwein.) Wallr.,Tremella gemmata Lév., and Exidia gemmata (Lév.) Bourdot & Maire.

Etymology

Exidia, the generic name, means exuding or staining, and both terms seem appropriate because these jelly fungi do look like exudations when moist and like dark stains on wood when they dry out.

The specific epithet nucleata comes from the Latin noun nucleatus, meaning a little nut or kernel; it is a reference to the opaque white nodular inclusions of calcium oxalate within the otherwise translucent and often largely transparent fruitbodies.

Identification guide

Exidia nucleata, closeup of fruitbody

Fruitbody

Gelatinous irregularly hemispherical or pustular (sometimes brain-like) forming blobs up to 1cm across, often coalescing to form much larger jelly-like patches, whitish with opaque Calcium oxalate inclusions in the form of pure white nodules (rather like fresh frog spawn containing white rather than black embryonic tadpoles). When dried out this fungus forms a thin brownish membrane that is easily overlooked.

 

Spores

Allantoid (sausage-shaped), smooth, 8.5-14 x 3.5-5µm; inamyloid; borne in sets of four on elongated, stalked basidia, (In contrast, the basidia of Exidia thuretiana are pear shaped to spherical and unstalked.)

Spore print

White.

Odour/taste

Not distinctive.

Habitat & Ecological role

Mainly on dead and decaying hardwood, particularly Sycamore, Beech and Ash but also quite commonly on alders, willows, hawthorns, elms, oaks and elder.

Season

Found throughout the year but most often see during autumn and winter in Britain and Ireland.

Similar species

Exidia thuretiana is similar but usually more opaque; it lacks the white crystalline inclusions that are characteristic of Exidia nucleata.

Tremella mesenterica is usually yellow and has a brain-like structure, but it does also have a (rare) white form.

Exidia nucleata, Crystal Brain fungus, growing on dead beech timber

Culinary Notes

This jelly fungus is of dubious edibility, and in any case it is too insubstantial to be worth collecting for food. We therefore class it as being of no culinary value.

Reference Sources

Pat O'Reilly (2016) Fascinated by Fungi; First Nature

Lincoff GH. (1981). National Audubon Society Field Guide to North American Mushrooms. New York, NY: AA Knopf.

British Mycological Society (2010). English Names for Fungi

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

Acknowledgements

This page includes pictures kindly contributed by Simon Harding.

Top of page...


Pat O'Reilly

If you have found this information helpful, we are sure you would also find our book Fascinated by Fungi by Pat O'Reilly very useful. Author-signed hardback copies at a special discount price are available here...

Other nature books from First Nature...