Crystal Brain

Crystal Brain (Myxarium nucleatum, formerly Exidia nucleata) is a pale jelly fungus best known for the small hard white specks embedded in its otherwise glassy tissue. These nuclei are mineral inclusions, and they are what give the species both its scientific epithet and its most reliable field character.

The fungus forms low, rounded to irregularly folded gelatinous lumps that emerge from cracks in bark or from the cut ends of logs, often in rows or clusters that later merge. Fresh and well-soaked material can be so transparent that the bark texture shows through it, and a cluster on a wet log can genuinely resemble a small patch of frogspawn.

Myxarium sits in the Auriculariales alongside Exidia, and the species was long treated within that genus. Modern classification separates it on microscopic grounds, but in the field the two remain a natural group of wood-inhabiting jellies to be compared with one another.

Fruiting body

Rounded to pillow-shaped gelatinous lumps 5–20 mm across, often numerous and fusing into irregular convoluted masses several centimetres long. The surface is smooth to shallowly folded, glistening when wet, and the shape is generally lower and more blob-like than the tall folded ridges of some Exidia species.

The crystalline nuclei

The defining feature. Scattered through the jelly are minute opaque white grains, usually well under a millimetre across, composed of calcium oxalate. Hold a lobe up to daylight and they show as a fine white speckling suspended within the clear tissue. No other common whitish jelly shows this so consistently.

Colour

Watery white, colourless-translucent or very pale greyish, sometimes with a faint buff or pinkish flush in age. Drying material becomes greyish and film-like, pressed thinly against the wood.

Flesh and spore print

Flesh soft, watery, gelatinous, collapsing easily when squeezed, without fibrous tissue, ring, volva or stipe, and with no bruising reaction. Spore print white.

Crystal Brain grows on dead broadleaved wood in damp conditions: fallen branches, logs, stumps and especially the sawn ends of stacked timber where water collects. Beech, ash, hazel, sycamore and elm are among the commonly recorded substrates, and it is often found on wood already softened by decay.

It fruits mainly from autumn through winter into spring, favouring mild wet spells, and can be found in almost any month where humidity is consistently high. The species is widespread across temperate Europe and is recorded from North America and other parts of the Northern Hemisphere.

Myxarium nucleatum is a saprotroph of dead broadleaved wood, contributing to white rot in branches and logs that are already well wetted. It fruits from mycelium running in the outer layers of the wood, pushing gelatinous lumps out through bark fissures and cut surfaces.

The calcium oxalate crystals that give the species its name are a by-product of fungal metabolism; many wood-decay fungi precipitate oxalate as they mobilise minerals from their substrate, but here the crystals aggregate into visible grains within the fruiting body. As with other jelly fungi, the water-retaining tissue allows repeated cycles of drying and rehydration, spreading spore release over a long period.

Exidia thuretiana (White Brain) is the main confusion: it is similarly pale and translucent but its jelly is clear throughout, lacking the embedded white grains, and it tends to form longer folded ridges rather than low rounded lumps. Pale immature Tremella fruiting bodies can also resemble it, but they gain yellow or brown pigment as they expand.

Exidia recisa (Amber Jelly Roll) is amber-brown and attached at a narrow point, quite unlike the broad, grainy, whitish cushions here. Slime moulds in the plasmodial stage sometimes appear as clear jelly on wet logs, but they lack a defined fruiting-body outline and typically flow across the surface in a network rather than sitting as discrete lobes.