Leafy Brain Identification Guide

The first impression

You usually see the Leafy Brain before you can name it, because nothing else in the autumn wood looks quite like a wet brown rosette stuck to a log. From two or three metres it registers as a dark, glistening clump the size of a fist, sitting on a fallen conifer trunk or on the underside of a dead attached branch. Get closer and the clump resolves into a stack of thin, wavy, leaf-like lobes arising from a shared base, translucent enough at the edges that light passes through them and picks out an amber core.

The overall shape is a frilled rosette, not a brain and not an ear, and that distinction carries most of the identification. Individual clusters run from 3 to 10 cm across, occasionally larger where several have fused along a crack in the bark.

The setting that supports the identification

Stand back and look at the wood itself. Phaeotremella foliacea in the strict sense is associated with conifer timber: spruce, pine, fir and larch stumps, logs and dead branches, usually in damp, shaded, mossy parts of a plantation or a mixed wood. It is not a soil fungus and it is not found on live sapwood.

Now look at the same piece of wood for a thin, leathery, greyish to buff crust with a smooth, slightly wrinkled underside. That is Stereum sanguinolentum, and it matters, because the Leafy Brain is a mycoparasite: it lives on the mycelium of that crust fungus rather than digesting the wood directly. Finding the host crust on the same log, often within a hand's width of the jelly, is one of the strongest supporting characters you can record, and it is available to anyone with eyes and no equipment.

Reading the lobes

There is no cap, no stem, no gills, no pores and no teeth, so the reading routine is different from an agaric. Work through the lobes instead.

Shape. Each lobe is a flattened, wavy plate 1 to 4 cm across, thin in section, with an undulating and sometimes shallowly lobed edge. Lobes arise crowded from a narrow common attachment and lean outward, so the whole fruit body has an open, layered, almost rosette-like architecture. Old clusters become denser and more crumpled as new lobes push through.

Colour. Fresh material ranges from pale cinnamon and warm reddish-brown through rich chestnut to dark date-brown. Very old or sun-exposed clusters darken almost to black at the tips. Hold a lobe up against the sky: the thinner areas glow translucent amber-brown, which is a useful check that you are looking at a jelly fungus and not a soft bracket.

Surface. Both faces of each lobe are smooth, glossy when wet and matte when starting to dry. There is no velvety outer face and no distinct upper and lower differentiation, because the spore-producing layer coats both sides of every lobe.

Texture, flesh and how weather changes it

Pinch a lobe. It is gelatinous, soft and elastic, and it springs back to shape rather than staying dented. Tear it and the break is smooth and structureless: uniform jelly all the way through, with no skin, no fibres, no separate flesh layer and no latex. Nothing changes colour at the tear.

Water content transforms the appearance completely. A dry spell shrinks the whole cluster to a hard, dark, scab-like crust pressed against the bark, easily overlooked as a stain. A night of rain rehydrates the same cluster back to a plump rosette within hours. If you find a suspicious dark patch on a spruce log in dry weather, mark it and come back after rain; that ability to revive repeatedly is characteristic of the jelly fungi as a group.

The spore-bearing surface and a spore print

Because the hymenium covers both surfaces of every lobe, spores are released in all directions. To take a deposit, cut a couple of well-hydrated lobes, suspend them over a glass slide or a piece of dark card inside a closed box with a drop of water to keep humidity high, and leave overnight. The deposit is white and often sparse, showing best as a pale film on dark glass.

Under a microscope the genus character is unmistakable: the basidia are divided longitudinally into four cells by vertical septa, giving the cross-partitioned appearance shared by Tremella and its relatives. Spores are broadly ellipsoid to subglobose, smooth and hyaline. If you can see those cruciately septate basidia, every bracket, crust and disc look-alike is eliminated at a stroke.

Substrate and season

Fruiting runs from late summer through autumn and continues into winter wherever there are mild, wet spells; frost damages exposed lobes but the base often regenerates. Look on the shaded, lower faces of logs and on the undersides of dead branches still attached to standing trees, where humidity holds longest. Clusters recur year after year on the same log for as long as the host crust persists.

Separating it from similar jellies

Phaeotremella frondosa is the closest relative and the main pitfall. It is generally larger and paler, more ochre- to tan-brown, with broader and more upright lobes, and it grows on hardwood, particularly oak, where it parasitises Stereum hirsutum. Host wood plus overall tone separates the two in the field better than any measurement.

Tremella mesenterica is bright golden-yellow to orange, and its fruit body is a mass of convoluted folds rather than distinct flat leaves. Even faded specimens keep a yellow core visible when a lobe is torn.

Auricularia auricula-judae forms single ear- or cup-shaped bodies rather than a rosette of many lobes, is thicker and more rubbery, and has two clearly different faces: a smooth, veined inner surface and a minutely velvety, greyish outer surface. Rosette versus ear is the quickest test.

Exidia glandulosa and E. nigricans are blackish to very dark olive-brown, lumpy and blobby rather than leafy, and their surfaces are peppered with tiny wart-like pimples. They are hardwood fungi, most often on oak and hazel.

Exidia recisa is amber to reddish-brown and translucent, but forms single top-shaped or wedge-shaped bodies attached by a narrow point, usually on willow.

Ascocoryne sarcoides starts as purplish-pink gelatinous blobs, a completely different colour, and matures into small discs with a defined rim.

A working field sequence

1. Identify the wood: conifer points to P. foliacea, hardwood to P. frondosa.
2. Confirm the growth form is a rosette of many thin wavy lobes, not a single ear or a folded mass.
3. Check colour: cinnamon to dark date-brown, translucent at the edges.
4. Pinch and tear a lobe: elastic jelly, uniform inside, no colour change.
5. Search the same log for a greyish Stereum crust as the likely host.
6. Take a humid-chamber deposit and expect white.