Branched Oyster Mushroom

The Branched Oyster is set apart from every other member of its genus by what happens where the gills meet the stem. Instead of simply running down and fading out, they converge and fuse into a conspicuous raised network of ridges that wraps the stem, a feature visible at arm's length once you know to look for it.

The fruit bodies are also more trumpet-like than in other oysters, with deeply depressed, funnel-shaped caps on comparatively long stems that branch repeatedly from a common base. A mature cluster resembles a bouquet or a cluster of horns, which is the origin of both the Latin epithet cornucopiae and the English names.

It is a common late-spring and summer species of European and Asian broadleaved woodland, particularly on elm, and belongs to the same group of wood-decomposing white-spored fungi as the common and Phoenix oysters.

Cap

The cap is 4-12 cm across, convex at first with an inrolled margin, then rapidly becoming deeply depressed and funnel- or trumpet-shaped. The surface is smooth, dry to slightly greasy when damp, and cream, ivory or pale ochre, darkening to buff or tan with age. The margin is thin, often wavy and lobed, and sometimes splits radially.

Gills

Gills are strongly decurrent, crowded, white to cream, and run far down the stem. Near the base they branch, cross-connect and fuse into a raised reticulate network of ridges that sheathes the stem, the definitive character of this species.

Stipe

The stem is 2-8 cm long, eccentric to almost central, whitish, firm, and typically branched or fused with several others at a common base so that many caps rise together in a bouquet from a single point on the log.

Flesh and spore print

Flesh is white, moderately thick at the centre and thin at the margin, unchanging when cut, with a mealy or floury smell. The spore print is white to pale lilac.

This fungus fruits on dead and dying broadleaved wood, most characteristically elm, but also oak, beech, ash, hornbeam, poplar and maple. It grows from stumps, fallen logs, standing dead trunks and exposed roots, often forming large branched clusters that can carry a dozen or more caps.

It is widespread through Europe and temperate Asia. Fruiting starts in late spring, peaks in summer, and continues into autumn, making it one of the earlier large wood fungi of the year in temperate woodland, and it will often reappear from the same stump across successive seasons.

The Branched Oyster is a saprotrophic white-rot fungus that also behaves as a weak parasite on stressed and dying broadleaved trees. It degrades lignin along with cellulose in the sapwood and heartwood, leaving pale, soft, fibrous residual wood and gradually hollowing out stumps and standing trunks.

By breaking down large-diameter hardwood it opens up the interior of dead trunks, creating cavities and soft substrates that are exploited by beetles, other invertebrates and hole-nesting birds. Like its relatives, its mycelium can also capture nematodes in the wood, supplying nitrogen that dead timber cannot provide on its own.

Pleurotus ostreatus is greyer, thicker-fleshed, almost stemless and its gills simply run down and stop without forming a network. Pleurotus pulmonarius is paler and thinner with a short lateral stem, but again lacks the raised reticulum on the stem. Checking the stem where the gills converge separates all three in seconds.

Hypsizygus ulmarius grows on elm as well, but has a broad convex cap on a stout central stem with gills that are notched rather than decurrent. Lentinus species have tough, leathery flesh and finely toothed gill edges. Clitocybe geotropa and other funnel-shaped soil fungi may match the cap shape, but they grow from ground litter with a central stem and never form branched clusters on wood.