Tremella encephala Identification Guide

First impression and where you are standing

This is a cold weather find on conifer wood. You are usually in a plantation or a mixed wood, working along a fallen pine or spruce trunk, a stack of extracted logs, or a weathered stump with the bark peeling away. Scattered along the exposed wood are small, firm jelly lumps, 1 to 4 cm across, pinkish brown to purplish brown, glistening after rain. From a couple of paces they look like blobs of solidified resin or discarded gum. Close up, the surface resolves into deep convolutions and folds that genuinely evoke a miniature brain, which is what the epithet records.

Register the substrate carefully at this stage. Look along the same log for thin, tough, buff to greyish crusts with a smooth or slightly wrinkled surface and a paler, fibrous edge. Those crusts are Stereum, and their presence on conifer wood is not incidental to the identification. This jelly fungus is a parasite of a particular one of them, and where the host is absent the parasite will not be.

The overall form

Fruit bodies begin as small cushions and expand into rounded to irregular, convoluted masses with lobed, brain like folds. Individuals sit alone or in short rows following a crack in the wood, and neighbours sometimes fuse into a longer ridge. The consistency is gelatinous but distinctly firm, more like a rubber eraser than a soft jelly, and a fresh piece resists denting with a thumbnail.

Colour ranges from pale pinkish buff through reddish brown to a dull purplish brown, sometimes almost translucent at the margins with a darker interior showing through. In dry weather the whole thing shrivels to a hard, dark, resinous scab welded to the wood, easily overlooked, and swells back into shape within hours of rain.

Cut it in half: the single decisive character

Slice a fruit body vertically with a sharp blade and look at the cut face. Inside the gelatinous outer layer sits a firm, chalky white to pale ochre solid core, sharply demarcated from the translucent jelly around it, occupying a good part of the centre.

That core is not the parasite. It is host tissue, a swollen mass of Stereum mycelium that the fungus induces and then feeds from, effectively growing its own larder inside itself. No other common jelly fungus on conifer wood shows so clean and consistent a white centre, and once you have seen it the species needs no further confirmation in the field. Always cut. A specimen judged from outside alone can easily be filed under the wrong name.

The spore bearing surface

There are no gills, pores, teeth or veins. The whole outer surface of the fruit body is fertile, smooth to slightly waxy, and faintly shining when moist. Under a hand lens it stays featureless apart from the folds themselves, which increase surface area rather than serving as a distinct hymenial structure. If you find anything resembling ribs, spines or a pored layer, you are not looking at a Tremella.

Taking and reading the spore print

Jelly fungi print poorly compared with gilled mushrooms, so give it time and control the humidity. Cut a fresh, well hydrated fruit body free of the wood, rest it on a glass slide or on dark card, and cover it with a box containing a scrap of damp tissue so that it does not dry out. Leave it overnight. What you get is a sparse white to very pale yellowish deposit, sometimes only a faint bloom that you see best by tilting the card to the light.

Microscopy is easy and rewarding. A squash of the surface layer shows basidia divided longitudinally into four cells by cross walls, the classic cruciately septate basidium of the genus, along with broadly ellipsoid to nearly spherical, smooth, colourless spores. Clamp connections are present, and secondary blastospores or yeast like budding cells may also appear, which is normal for the group. Look too for the point where the parasite hyphae contact host hyphae in the region of the white core.

Host, substrate and season

The species is a mycoparasite, growing not on the wood itself but on the mycelium of Stereum sanguinolentum, a resupinate crust of dead conifer wood whose fresh surface reddens where it is scratched. Its practical substrates are therefore fallen pine and spruce trunks and branches, stumps, and cut timber left in the forest, chiefly in coniferous plantations and mixed woodland.

Season runs from autumn through winter into early spring. Like several jelly fungi it is essentially frost tolerant, going hard in cold snaps and rehydrating with the next thaw, so mid winter walks are among the best times to search. It is easily missed in summer, when it may be reduced to a dark varnish on the log.

Separating the closest look-alikes

Yellow Brain, Tremella mesenterica, has the same convoluted form but is a vivid golden yellow to orange, occurs on dead hardwood twigs and branches, and parasitises Peniophora crusts. Cut it and you find jelly all the way through, without a firm white centre.

Tremella aurantia is deeper orange yellow and also encloses a pale host core, but its host is the hairy hardwood crust Stereum hirsutum, so the substrate is broadleaved wood and the colour is far warmer.

Leafy jelly fungi in the Tremella foliacea group are brown to reddish brown but build a rosette of thin, flattened, wavy leaf like lobes rather than a compact convoluted cushion, and the outline is loose and frilly rather than solid.

Exidia species, such as the black witches butter of oak twigs, are darker, softer and more collapsing, often blackish or olive black, and many carry scattered pimple like warts on the surface. None has a white internal core.

Among the cup fungi, Ascocoryne sarcoides forms purple pink gelatinous blobs and small discs on hardwood; the mature stage is disc shaped rather than brain like, and microscopically it produces spores in asci, not on cruciately septate basidia. Neobulgaria pura is paler pinkish and forms rubbery, top shaped cups on beech, again with a clean cup outline.

Finally, on very old logs, weathered resin lumps and hardened sap can mimic the fungus at a distance. They are brittle, snap rather than flex, and reveal no internal structure when cut.