Leafy Brain

Leafy Brain (Phaeotremella foliacea, long known as Tremella foliacea) is a large brown jelly fungus whose fruiting body is built from many thin, undulating lobes radiating from a common base. The overall effect is closer to a rosette of wet lettuce or a clump of brown seaweed than to the compact folded blobs of the yellow jellies.

The genus Phaeotremella was separated from Tremella on molecular grounds and gathers together the brown-fruited mycoparasites of the group. Members share the divided basidia of the Tremellomycetes and the same habit of parasitising other wood-inhabiting fungi, but differ in their darker, often reddish or purplish-brown pigmentation.

Phaeotremella foliacea in the strict sense is associated with conifer wood, where its host is the resin-stained crust fungus Stereum sanguinolentum. Very similar brown jellies found on broadleaved wood are now generally placed in Phaeotremella frondosa, a distinction that is hard to make in the field but useful to know when recording the substrate.

Fruiting body

A large rosette or cluster 5–20 cm across, occasionally more, composed of numerous thin, flattened, wavy lobes arising from a compact common base. Individual lobes are only a millimetre or two thick, translucent at the margin, and crimped or ruffled along the edge. The whole structure is soft, floppy and gelatinous, sagging under its own weight when large.

Colour

Warm brown, often with reddish, cinnamon or purplish tones, sometimes almost date-brown in the thicker parts and much paler and more translucent at the lobe edges. Fading to dull tan in age and shrinking to a dark, hard, almost black crust when thoroughly dried.

Attachment and flesh

Fused into a single tough attachment point on the wood, from which all the lobes radiate. Flesh gelatinous, translucent, uniform, with no fibrous core, no ring, no volva and no true stipe. Cutting produces no colour change beyond the natural translucency of the tissue.

Spore print

White, despite the brown fruiting body. The entire lobe surface is fertile.

This species grows on dead conifer wood: fallen trunks, stumps, cut ends of logs and large branches, with spruce and pine the most frequent hosts. It favours damp, shaded forest situations where the wood stays wet, and it often reappears in the same spot in successive years as long as the log persists.

Fruiting runs from late summer into late autumn, sometimes lingering into early winter in mild areas. The species is widespread across the coniferous and mixed forests of the temperate Northern Hemisphere, including much of Europe, northern Asia and North America.

Like its yellow relatives, Leafy Brain is a mycoparasite rather than a direct wood decayer. It attacks the mycelium of Stereum sanguinolentum, a thin resupinate to bracket-forming crust fungus of conifer wood that bleeds a red juice when scratched while fresh. Finding that crust on the same log is a strong confirmation of the identification.

The host carries out white rot of the conifer wood, and the Phaeotremella diverts nutrients from that established mycelium. The gelatinous, high-surface-area rosette maximises the fertile area exposed to air, and its ability to dry to a crust and rehydrate lets a single fruiting body shed spores over several weeks of alternating wet and dry weather.

Phaeotremella frondosa is essentially identical in form but grows on broadleaved wood, particularly oak and beech, where its host is Stereum rugosum; substrate is the practical field separator. Auricularia auricula-judae (Jelly Ear) is also brown and gelatinous but forms distinctly cupped, ear-shaped structures with a smooth or veined inner face and a minutely velvety outer face, rather than a rosette of thin ruffled lobes.

Tremella mesenterica and Tremella aurantia are yellow to orange and much more compactly folded. Exidia glandulosa (Black Witch's Butter) is far darker, nearly black, and forms warty cushions studded with tiny pimples rather than smooth leafy blades.