Never eat a wild mushroom identified only from a website, a book or an app. Have every find checked in person by an expert, such as a mycological society.
Identification
The jelly ear forms rubbery, translucent fruit bodies 3–10 cm across, often shaped remarkably like a human ear. The outer (upper) surface is finely velvety and greyish to reddish brown; the inner surface, which produces the spores, is smooth or folded into vein-like ridges and slightly shiny. In dry weather the fruit bodies shrink and become hard and brittle, reviving after rain. The spore print is white.
Microscopically, Auricularia has transversely septate basidia, typical of the order Auriculariales. The European A. auricula-judae has been separated by DNA studies from the Asian species grown commercially, such as Auricularia heimuela and A. cornea (the larger, hairier "cloud ear"); much of the dried "black fungus" sold belongs to these Asian species.
Habitat and ecology
Jelly ear is a saprotroph and weak parasite on dead and dying wood of broadleaved trees. In Europe it is famously common on elder (Sambucus nigra), but it also grows on beech, sycamore, ash and other hardwoods. It fruits all year in mild climates, most abundantly in late autumn and winter, and is widespread across Europe. Closely related species occur throughout the temperate and tropical world.
Uses and importance
Wood ear mushrooms have little flavour but a pleasant crunchy, gelatinous texture and absorb sauces well. They are a classic ingredient in Chinese hot-and-sour soup, stir-fries, salads and dumpling fillings, and are mostly sold dried. In traditional Chinese practice Auricularia has long been used as a food with health associations. Laboratory and animal studies have examined its polysaccharides; an early clinical report linked large amounts eaten in a meal to reduced platelet aggregation. There is no evidence that it treats disease, and in the EU health claims may only be made if authorised under Regulation (EC) No 1924/2006. If you take anticoagulants, ask your doctor before eating large amounts or taking supplements.
Cultivation
Asian Auricularia species are grown on a very large scale, mainly in China, on bags of sterilised or pasteurised hardwood sawdust and on logs. Spawn run takes place at roughly 22–28 °C; fruiting needs high humidity, light and good ventilation. The fruit bodies tolerate drying well, which makes the crop easy to store and transport. The European jelly ear can also be grown on logs of elder or other hardwoods but is rarely cultivated commercially.
Safety and edibility
Jelly ear is edible but should always be cooked. Dried wood ear must be rehydrated in clean water in the refrigerator and used soon: poisonings with bongkrekic acid, a toxin produced by the bacterium Burkholderia gladioli pv. cocovenenans, have been reported in China after wood ear or other mushrooms were left soaking for a long time at room temperature. Bongkrekic acid poisoning can be fatal, so seek emergency help immediately if anyone becomes ill after eating long-soaked mushrooms. If you collect it in the wild, have the identification confirmed in person by an expert, such as a mycological society or trained mushroom adviser.
If you suspect mushroom poisoning, call your local emergency number or poison centre straight away, even before any symptoms appear, and keep the remains of the mushrooms.
Look-alikes
Jelly ear has no dangerous look-alikes in Europe. Other jelly fungi such as Exidia glandulosa (black, warty, brain-like) and Tremella mesenterica (yellow brain) differ in colour and shape. The Asian Auricularia cornea (cloud ear) is larger and has a hairier upper surface. Tree ear-like cup fungi, for example Peziza species, are brittle, not rubbery, and grow on soil or wood without the velvety outer surface.
Around the world
Worldwide, wood ear is among the most important cultivated mushrooms by volume, almost entirely from Asian production. In Europe, the native jelly ear is a common sight on elder hedges, while dried "black fungus" in Asian supermarkets generally comes from cultivated Asian species.