Tiger Sawgill

Lentinus tigrinus is the type-like representative of a group of tough, leathery, wood-rotting agarics whose flesh is far more like a bracket fungus than a typical mushroom. The genus Lentinus belongs in the Polyporaceae, alongside Polyporus and Trametes, and several of its species blur the line between gills and pores; some relatives even produce a hymenophore that is gill-like near the stem and pore-like at the margin.

The Tiger Sawgill is recognised by its funnel-shaped, cream to buff cap covered with small, dark brown to almost black, flattened fibrous scales that are densest at the centre, by white gills that run far down the stem and are minutely toothed along their edges, and by a firm scaly stem that darkens toward the base. Fruit bodies are typically small to medium and grow singly or in tight clusters from waterside deadwood.

The species is also known for a curious closed form, once described as a separate fungus under the name Lentodium squamulosum, in which the cap margin never lifts away from the stem and the gills stay enclosed inside a puffball-like chamber. This form is now understood to be a single-gene variant of ordinary Lentinus tigrinus, and both types can arise from the same parentage.

Cap

2-10 cm across, convex when young with an inrolled edge, soon becoming shallowly then deeply funnel-shaped with a depressed or navel-like centre. The ground colour is white, cream or pale tan, overlaid with small, flattened, radially arranged fibrous scales in dark brown, greyish-brown or blackish tones, densest over the centre and thinning outward. In dry weather the margin splits and curls upward.

Gills

White to cream, becoming buff or slightly pinkish-tan with age, crowded, narrow, and strongly decurrent, running well down the stem. The edges are finely and irregularly serrated, best seen with a lens. Bruised or ageing gills may develop rusty or brownish spots.

Stipe

2-8 cm long, 0.3-1 cm thick, central to slightly eccentric, tough and solid, often curved. It is white to cream at the apex and progressively covered with dark brown scurfy scales downward, so the base is typically dark brown to blackish. There is no true ring, although a scaly zone may mark where the cap margin was attached.

Flesh and spore print

The flesh is white, thin, tough and elastic, unchanging when cut, and dries hard. The spore print is white; spores are smooth, cylindrical to ellipsoid. In the closed secotioid form the gills remain sealed inside the unopened cap, which looks like a scaly, stalked ball.

Lentinus tigrinus is a fungus of wet lowland woodland and riverine habitats. It fruits on dead hardwood, showing a strong preference for willow, poplar, cottonwood and alder, and also occurring on elm, ash, maple and oak. Typical substrates are fallen branches and logs lying in floodplains, on riverbanks, in swamp forest and around ponds and drainage ditches, often on wood that has been soaked and then exposed as water levels drop.

Fruiting runs from late spring through summer into early autumn, usually following a wet spell. The species is widespread in temperate Europe, temperate and subtropical Asia and North America, and reaches into subtropical zones, but it is patchy in occurrence and tends to be locally abundant along water courses while absent from drier woodland nearby.

This is a saprotrophic white-rot fungus. Its mycelium degrades lignin as well as cellulose, and colonised willow and poplar wood becomes pale, soft and stringy. The species is well adapted to substrates that alternate between saturation and drying, and its tough fruit bodies withstand desiccation that would destroy a fleshy agaric.

By specialising in soft, fast-growing riparian hardwoods, Lentinus tigrinus helps recycle the large volumes of wood shed by willows and poplars in flood-disturbed habitats, where mechanical damage and waterlogging constantly create fresh dead material. Its closed secotioid form is of particular interest to mycologists, since the difference between an open, spore-dispersing cap and a sealed chamber turns out to hinge on very little genetic change.

Neolentinus lepideus is the main confusion. It is larger and more robust, with paler reddish-brown to tan scales on a cream cap that is flat or only shallowly depressed rather than funnel-shaped, coarser saw-teeth on the gills, and a strong preference for conifer wood and worked timber rather than waterside hardwood. Lentinus arcularius and Lentinus brumalis, growing on similar branches, have true pores on the underside instead of gills.

Panus species such as Panus conchatus have hairy or velvety caps without distinct dark scales and lilac-tinged gills with even edges. Small Pluteus species growing on the same waterlogged wood are soft-fleshed, with free gills that turn pink and a pink spore print, quite unlike the tough flesh, decurrent gills and white print of the Tiger Sawgill.