Yellow brain fungus

Pictures and a message from Clive Knight:

Walking round the reserve today, I saw this bright yellow fungus growing on an old Oak branch. I have no idea what it is. Can anybody help?

To which our Tree Officer, Rich Murphy, replied:

Nice find! I’ve only seen it a handful of times in the reserve. I know it as Yellow Brain Fungus (Tremella mesenterica) but it is also commonly known as witches’ butter.

Yellow brain fungus is an interesting species. It grows on dead timber but it doesn’t feed on the wood; it feeds on various kinds of crust fungus that are themselves feeding on the wood. This means that Tremella mesenterica is a mycoparasite, a fungus that feeds on other fungi.