Cloud Ear

Cloud Ear is one of several closely related Auricularia species that form gelatinous, ear-shaped brackets on dead wood. It is widely referred to under the name Auricularia polytricha, though current treatments generally apply Auricularia cornea to the widespread warm-climate species.

The genus belongs to the Auriculariales, an order of jelly fungi whose basidia are divided by cross walls — a microscopic feature that sets them apart from the gilled fungi despite both producing spores on an exposed surface. In Auricularia the fertile surface is simply the smooth underside of the bracket, with no gills, pores or teeth.

Its distinguishing features are the dense coat of fine hairs on the upper surface, giving a velvety or felted look, and the thick, tough, strongly rubbery consistency of the flesh. It shrivels to an unremarkable dark flake in dry weather and swells back into shape when rain returns.

Fruiting body

Brackets are 3–12 cm across, ear-shaped, cup-shaped, or irregularly lobed and wavy, often overlapping in tiers along a branch. They are attached laterally by a narrow point or a short stub rather than by a true stipe, and the margin is often inrolled when young.

Surfaces

The upper (sterile) surface is densely covered in short, fine greyish hairs, giving a matt, velvety or frosted appearance; the colour beneath the hairs is greyish-brown to purplish-brown. The lower (fertile) surface is smooth to slightly wrinkled or shallowly veined, purplish-brown, reddish-brown or greyish, and glistening when fresh.

Flesh and spore print

Flesh is gelatinous but notably firm and rubbery, typically 1–3 mm thick, translucent to brownish in section, and elastic when squeezed. On drying it shrinks dramatically into a hard, dark, brittle plate and rehydrates readily. The spore print is white.

Cloud Ear grows on dead and dying hardwood — fallen branches, logs, stumps and standing dead trunks — and occasionally on the dead parts of living trees. It shows a preference for broadleaf trees of many kinds and is frequent in secondary forest, plantations, roadside trees and gardens.

It is chiefly a species of tropical, subtropical and warm-temperate regions across Asia, Africa, the Pacific, Australasia and the Americas. Fruiting follows rain and can occur at any time of year where conditions stay warm and humid, with brackets appearing in dense clusters after wet spells.

The species is saprobic and causes a white rot, degrading lignin as well as cellulose so that colonised wood becomes pale, soft and fibrous. Its mycelium permeates the outer sapwood of dead branches, and fruiting bodies erupt through the bark in rows along cracks.

Spores are produced on the smooth lower surface and released into the air. The gelatinous flesh is an adaptation to intermittent moisture: the fungus dries down to a resistant flake during dry weather and resumes spore production within hours of rewetting, allowing many cycles of spore release from a single bracket.

Auricularia auricula-judae, the Jelly Ear, is thinner, more translucent and more distinctly ear-shaped, with only a sparse fine down on the upper surface and a lower surface that is more strongly veined and folded; in Europe it is strongly associated with elder. Auricularia mesenterica forms tiered, hairy, concentrically zoned brackets whose underside is deeply wrinkled and purplish, quite unlike a smooth ear.

Exidia glandulosa and relatives form black, brain-like or blob-shaped gelatinous masses with pimpled surfaces rather than flattened brackets, and are much softer. Tremella species are frilly and lobed rather than ear-like. Among these, the combination of dense grey hairs above, a smooth purplish-brown fertile surface below, firm rubbery flesh and a white spore print points to Cloud Ear.