Reishi

Reishi is the best known of the lacquered Ganoderma species, the group whose upper surface carries a natural resinous coating that gives it the appearance of polished varnish. In fresh condition the bracket looks as though it has been shellacked, shading from a white or bright yellow growing margin through orange and chestnut to deep mahogany or oxblood red at the point of attachment.

The name Ganoderma lucidum has historically been applied very broadly to varnished brackets worldwide, but molecular work has split the complex into a number of regionally distinct species. The East Asian fungus long cultivated and depicted in Chinese art is now generally treated as Ganoderma lingzhi, while G. lucidum in the strict sense is a European and North American species, with G. tsugae on conifers in North America and further taxa elsewhere. In common usage all of them are called reishi or lingzhi.

The lingzhi form is one of the most frequently represented fungi in world art, appearing as a stylised motif on Chinese scroll paintings, carved jade, porcelain, furniture and textiles for many centuries, usually recognisable by its kidney-shaped cap, glossy surface and long curving stalk. Unlike the perennial Artist's Conk, reishi brackets are annual and produce a single season of tubes.

Fruiting body

A kidney-shaped, fan-shaped or occasionally circular bracket 5-25 cm across and 1-3 cm thick, hard and corky, either attached directly to the wood or, very characteristically, borne on a distinct lateral or off-centre stalk that may be several centimetres long. The upper surface is smooth, hard and conspicuously glossy, as though varnished, with concentric zones and radial wrinkles. Colour is banded, with a white to bright yellow growing edge behind which lie zones of orange, tan, chestnut and finally dark reddish mahogany toward the base. Old, weathered brackets dull down and are often dusted with brown spores.

Pores

The underside is flat, white to cream when fresh, ageing to pale buff and then brown, and made up of very fine round pores at roughly four to six per millimetre. Bruising or scratching turns the surface brown, though less dramatically than in the Artist's Conk. There is a single tube layer, up to about 2 cm deep, because the bracket is annual rather than stratified into yearly layers.

Stipe and context

The stalk, when present, is the same lacquered reddish brown as the cap, cylindrical, often irregular or twisted, and attached laterally so the bracket stands out like a paddle. The internal context is corky and fibrous, pale buff to cinnamon or pale brown, distinctly lighter than the deep brown context of many perennial polypores, and it is soft enough to cut with a knife when fresh.

Spore print

Rusty brown to cocoa brown. Under a microscope the spores are the classic Ganoderma type: ellipsoid, truncated at one end, with a double wall whose inner layer is covered in fine spines or pillars.

Ganoderma lucidum and its relatives grow on the stumps, buried roots, root collars and fallen trunks of broadleaved trees, with oak the most frequent host in Europe, alongside maple, beech, elm, plum, willow and other hardwoods. Brackets often emerge from the ground apparently rootless, but are in fact attached to a buried root or root plate, and the long stalk in such cases lifts the cap clear of the litter. Related lacquered species such as G. tsugae occupy conifers, particularly hemlock.

Fruiting is annual, with new brackets appearing from early summer and continuing through autumn, and the dead structures may persist through the winter in a dulled and weathered state. The complex as a whole is essentially cosmopolitan, with members in Europe, temperate and tropical Asia, North America, Africa, South America and Australasia, and it is cultivated on logs and on sawdust blocks on a very large scale in East Asia.

Reishi is a white rot fungus. Its enzymes break down lignin along with cellulose and hemicellulose, so the decayed wood becomes pale, soft, stringy and lightweight. It behaves both as a weak parasite, entering living trees through root and butt wounds and causing a slow root and butt rot that can eventually destabilise a mature tree, and as a saprotroph that continues to break down the stump and root system long after the tree has died.

By degrading the lignin-rich heartwood of large hardwood stumps it performs a decomposition step relatively few organisms can accomplish, releasing locked carbon and mineral nutrients back into forest soil and hollowing root plates into habitat for invertebrates. The tough, resinous, weather-resistant crust protects the fruit body through a long spore-producing season, and the enormous quantity of brown spores it releases settles as a visible film on the bracket and surrounding surfaces.

The Artist's Conk, Ganoderma applanatum, is the most likely confusion at a distance but has a dull, dry, lumpy, unvarnished grey-brown crust, no stalk, a chalk-white pore surface that bruises dark brown instantly, and a stratified perennial tube layer built up over successive years. Ganoderma australe likewise has an unvarnished crust and stacked annual tube layers.

Within the lacquered group, Ganoderma tsugae is nearly identical in gloss and shape but grows on conifers, especially hemlock, and tends to have a paler, thinner, whiter context. Ganoderma lingzhi, the East Asian lingzhi, differs in subtle context colour and spore dimensions and is separated mainly by geography and by microscopy. Ganoderma resinaceum is larger, more irregularly shaped, usually sessile or with only a stubby stalk, and has a softer crust that can be marked with a thumbnail when fresh.

Fomitopsis pinicola shares a shiny banded crust but the gloss is confined to a resinous red-orange band near the margin, the pore surface is cream and does not develop the deep mahogany tones, and the decay it causes is a brown rot leaving crumbly cubical residue rather than pale fibrous white-rotted wood.