Species of the Month - January 2017

Yellow Brain Fungus

Tremella mesenterica
 

Yellow Brain Fungus is a jelly fungus found on dead wood of standing trees or bushes.  In our area it is most often seen on Gorse.

Like all jelly fungi it swells up when wet and shrivels to a paper-thin skin when dry, but even when dried out it is usually visible owing to its bright colour and folded structure that prevents it lying flat on the branch.  The one in the photos above is halfway to drying out, after a few hours in the sun.

It often turns quite a dark orange as it dries.

We have 59 records of this fungus in the LNHG database, distributed between the months as follows:

Clearly it flourishes best in the depths of winter.  The distribution by host tree/bush is:

This is not reflected nationally, where gorse is the commonest host but with less than half the total records.  Other common hosts are ash, oak and beech, with many other broadleaved trees and bushes and the occasional conifer listed.

On the left, Yellow Brain Fungus on Birch, an unusual host in our part of the world.  The cluster on the right is on Gorse, its normal host.

Strictly speaking the tree or bush is not the "host" to the fungus but merely the substrate.  Yellow Brain Fungus does not feed on the wood of the tree, but on the mycelium of another fungus called Peniophora incarnata, which does feed on the wood.

On the left, Peniophora incarnata, and on the right its parasite, Yellow Brain Fungus.  Both are on gorse.  You will often find Yellow Brain fruitbodies on a bush without P incarnata fruitbodies, since the latter does not always have fruitbodies present, and the Yellow Brain does not feed on P incarnata's fruitbodies but on its mycelium within the wood which is not visible from the outside.  Yellow Brain fruitbodies are seen more often than those of P incarnata.

Our records of P incarnata are all on gorse or its close relative broom, but that may be because some of us are less confident of identifying it on other hosts!  Nationally, P incarnata is recorded on gorse slightly over half the time, with a variety of other broadleaves making up the rest.

The only species with which Yellow Brain Fungus can be confused is Tremella aurantia, which looks similar but is less glossy.  This fungus grows on the fruitbodies (not the mycelium) of Stereum hirsutum, a highly conspicuous fungus which always has many fruitbodies growing close together.  Therefore if there is no Stereum hirsutum present you know your yellow jelly is not T aurantia, and must be T mesenterica.  This is what Stereum hirsutum looks like...

S hirsutum is very common in our area, but its parasite Tremella aurantia has never been recorded in Argyll, or anywhere else in Scotland.  So if you spot a Yellow Brain Fungus lookalike devouring a Stereum hirsutum fruitbody, let us know about it!!
 

Please send in your Yellow Brain Fungus sightings using the form below, or email sightings@lnhg.org.uk with the details if you prefer.  If you are not sure of the identity of your fungus or of its host tree or bush, please send a photo to sightings@lnhg.org.uk, or put one on the LNHG Facebook page.