Train Wrecker

Neolentinus lepideus earned its English name from its habit of colonising creosoted railway sleepers, telegraph poles, mine props and bridge timbers, where its brown rot eventually crumbles the wood from the inside. It is one of the few gilled fungi to cause a brown rot, and that unusual biology is why it was pulled out of Lentinus into the small genus Neolentinus, which sits with the Gloeophyllales close to the brown-rotting bracket fungi rather than with the ordinary agarics.

In the field it is unmistakable once its combination of features is registered: a firm, dry, pale cap decorated with flattened brown scales, white gills that run down the stem and are notched into a coarse saw-toothed edge, and a tough scaly stem that often tapers into a rooting base wedged into a crack in the timber. The whole fruit body is leathery and long-lasting, and old specimens shrivel and harden rather than decaying away.

Because the species is at home on worked and treated wood as well as natural stumps, it is one of the fungi most likely to be encountered in industrial and urban settings: rail sidings, fence lines, decking, log stores and utility poles all support it, sometimes far from any forest.

Cap

5-15 cm across, occasionally to 30 cm, convex with an inrolled margin at first, expanding to flat or shallowly depressed. The surface is dry, whitish to cream or pale buff, and is patterned with flattened, appressed, reddish-brown to tan scales that are largest and most crowded toward the centre and thin out toward the margin. The margin often splits radially in age.

Gills

White to cream, discolouring buff or with rusty stains where bruised, broad, moderately spaced, and clearly decurrent, running some distance down the stem. The gill edges are coarsely and irregularly toothed, like a blunt saw blade, which is visible without a lens on mature specimens and gives the group the name sawgills.

Stipe

3-12 cm long, 1-3 cm thick, central or somewhat off-centre, firm and very tough. It is whitish above a poorly defined, hairy ring zone and covered below with brownish scurfy scales that echo those on the cap. The base tapers and often extends as a hard rooting projection into a crevice in the timber.

Flesh and spore print

The flesh is white, thick, tough and fibrous, unchanging when cut, and dries hard rather than rotting. Fruit bodies developing in dark or poorly ventilated places, such as inside cellars or under decking, can become bizarrely deformed antler-shaped stalks with no proper cap. The spore print is white, and the spores are smooth and cylindrical.

Neolentinus lepideus is strongly associated with conifer wood, above all pine, and also occurs on spruce, larch, fir and Douglas fir. It fruits on stumps, fallen trunks, buried roots and cut ends of logs in coniferous forest, and equally on processed timber: railway sleepers and ties, utility poles, mine timbers, fence posts, wooden decking, boat timbers and structural beams. It tolerates preservative-treated wood well, which is why it appears in places where few other fungi persist.

Fruiting occurs from late spring through autumn, with the main flush in summer, and single fruit bodies or small clusters may appear at almost any time in mild weather. The species is widespread across the temperate Northern Hemisphere, common in Europe, northern Asia and North America, and has been carried to other regions along with conifer plantations and imported timber.

This is a saprotrophic brown-rot fungus. Its mycelium removes cellulose and hemicellulose from the wood but leaves much of the lignin behind, so the residue turns brown, shrinks and breaks into cubical blocks that crumble to powder between the fingers. Brown rot is the norm among conifer-associated bracket fungi but is rare in gilled fungi, and Neolentinus is one of a very small group of agarics that do it.

Ecologically the fungus is a pioneer of large, dense conifer wood, including heartwood that many competitors cannot exploit. In natural forest it plays a part in returning carbon from fallen pine trunks to the soil; in built environments the same enzymatic machinery makes it the classic agent of decay in sleepers and poles. Its tough, water-resistant fruit bodies allow it to release spores over long dry spells that would shrivel a fleshy mushroom.

Lentinus tigrinus is the closest look-alike in shape, but it is smaller, its scales are darker brown to blackish on a whiter ground, its cap is more deeply funnel-shaped, and it grows on hardwood, especially willow and poplar in wet ground. Neolentinus ponderosus of western North America is a much larger, coarser species with paler, more scattered scales, fruiting on conifer stumps in mountain forest.

Pholiota squarrosa forms scaly clusters that recall Neolentinus at a glance, but its scales are upright and shaggy rather than flat, its gills are attached rather than long-decurrent with smooth edges, and it drops a rust-brown spore print. Lentinellus species share the sawn gill edges but are sessile or nearly so, with hairy, stemless fan-shaped caps and no scales.