Split Gill

Split Gill is among the most widely distributed fungi on Earth, recorded from every continent except Antarctica and from an enormous range of woody substrates. It forms small, stalkless, fan- or shell-shaped brackets, densely hairy and greyish-white above, growing in overlapping troops along dead branches, fence rails, cut stumps and sawn timber.

Its name comes from a structure found nowhere else in quite this form. The ridges on the underside look like gills, but each one is split lengthwise along its edge into two lips. In dry weather the lips curl apart and roll back, shielding the fertile surface; when rain returns they swell, close together and resume releasing spores. The whole fruiting body is leathery and desiccation-tolerant, capable of drying to a brittle crisp and reviving repeatedly over months.

The species is also a cornerstone organism in fungal genetics. Its mating system involves thousands of distinct mating types — more than any other known organism — meaning almost any two individuals that meet are compatible, and it has become a standard laboratory model for studying sexual compatibility and wood decay in fungi.

Fruiting body

Brackets are small, 1–5 cm across, fan-shaped, shell-shaped or deeply lobed and often fused laterally into overlapping rows. They are attached directly to the wood by a narrow point or a short lateral pad, with no true stem. The upper surface is densely covered in fine white to greyish hairs, giving a felted or woolly texture, and colour ranges from white through pale grey to greyish-brown, sometimes greening with algae on old specimens.

Gill-like folds

The underside carries radiating, gill-like folds coloured pinkish-grey, buff or lilac-grey. Under a hand lens each fold is split along its free edge into two halves that fold apart in dry conditions and press together when moist — the single unmistakable diagnostic feature of the species. The folds radiate from the attachment point to the margin, and they are tougher and more rubbery than true gills.

Flesh & spore print

The flesh is very thin, white and leathery-tough, flexible when wet and hard and brittle when dry, and it never becomes soft or fleshy. The margin is usually lobed and inrolled when dry. The spore print is white, from small, cylindrical, smooth spores.

It grows on dead hardwood of almost any kind — fallen branches, standing dead limbs, stumps, logs, sawn timber, fence posts, and stored or worked wood — and occasionally on conifers, on straw and on other plant debris. It favours sun-exposed, well-lit and drier positions such as woodland edges, hedgerows, city parks and stacked timber, where its drought tolerance gives it an advantage over softer fungi.

Distribution is essentially cosmopolitan, from tropical to cool-temperate zones on every inhabited continent, making it one of the most widespread macrofungi known. Fruiting bodies can be found in every month of the year: they dry out and shut down during drought and then rehydrate and resume spore production within hours of rain, so a single bracket may remain active across an entire season.

Schizophyllum commune is a saprophyte causing a white rot, degrading lignin and cellulose in the sapwood of dead branches and timber and leaving it pale and fibrous. It is an aggressive early coloniser of freshly killed and exposed wood, particularly wood in sunny, dry sites, and its ability to survive prolonged desiccation lets it hold territory that softer-fleshed decay fungi cannot occupy.

Biologically it is best known for its mating system. Two unlinked mating-type loci with hundreds of alleles each produce more than 20,000 mating types, so nearly any two mycelia that meet can fuse and reproduce sexually. That, plus its rapid growth in culture and its fully sequenced genome, has made it one of the most heavily studied model fungi for research into fungal sex, fruiting-body development and lignin degradation.

Crimped Gill (Plicaturopsis crispa) is the nearest look-alike, a small stalkless fan on hardwood twigs with wavy, fold-like ridges beneath, but its folds are crimped and blunt rather than split into two lips, and its upper surface is orange-brown with paler concentric zones rather than uniformly white-hairy. Stereum species such as Hairy Curtain Crust are also hairy fans on dead wood but have a completely smooth, unwrinkled underside with no folds at all.

Trametes and other small brackets have true round or angular pores instead of radiating folds. Bitter Oysterling (Panellus stipticus) forms small tan kidney-shaped brackets on hardwood with true, thin, unsplit gills and a short lateral stub of a stem, and its flesh is thinner and less woolly on top. In every case a hand lens on the underside settles it: only Split Gill has folds divided lengthwise into two curling lips.