Bear Lentinus

Lentinellus ursinus is one of the stemless sawgills, a distinctive group of small, tough, shelf-forming agarics in the family Auriscalpiaceae. That family is an odd assemblage that also contains the Ear-pick Fungus, Auriscalpium vulgare, and the coral-like Artomyces; what unites them is a set of microscopic characters, including finely spiny spores that stain blue-black in iodine.

In the field the genus is recognised by gills whose edges are cut into conspicuous, uneven teeth, as if trimmed with pinking shears. Lentinellus ursinus takes this further with an almost complete absence of a stem: the fan-shaped cap is attached directly to the wood by a broad or narrowed lateral point, and the surface immediately around that point is covered in dense dark hairs that give the species its bear-like name.

It is a common autumn fungus of northern hardwood forest, forming overlapping tiers on fallen logs. Fruit bodies are leathery, persist well, and are often found alongside other tough shelf fungi, so the sawn gill edges become the key that separates it quickly from the many stemless species with plain-edged gills.

Cap

2-10 cm across, fan-, shell- or kidney-shaped, attached laterally to the wood without a stem or with only a rudimentary stub. The upper surface is tan, cinnamon, reddish-brown or dark brown, usually darkest near the attachment and paler toward the margin. The base is densely covered with coarse, matted, dark hairs that thin out to a finely velvety or nearly smooth outer zone. The margin is thin, often wavy, and may be faintly zoned.

Gills

Radiating outward from the point of attachment, cream to pale pinkish-buff or tan, close, and narrowing toward both ends. Their most useful feature is the edge: coarsely, irregularly and often deeply saw-toothed, a character visible without magnification on mature fruit bodies. The gills discolour brownish where bruised or in age.

Stipe

Absent, or reduced to a short, hairy lateral pad. Fruit bodies attach directly to the log, frequently in overlapping tiers along a fallen trunk.

Flesh and spore print

The flesh is white to pale buff, thin, tough and pliable, drying hard. The spore print is white; spores are small, round to ellipsoid and covered in fine amyloid spines, a microscopic hallmark of the genus and its family.

Lentinellus ursinus fruits on dead hardwood, particularly beech, birch, maple, alder and other broadleaved trees, and only occasionally on conifers. It favours fallen logs and large branches lying on the ground in damp, shaded, mature woodland, and often colonises trunks that are already well rotted and partly covered in moss. Fruit bodies typically appear in overlapping rows and tiers along the upper side of a log.

The main fruiting season runs from late summer into late autumn, sometimes continuing after light frosts, since the tough fruit bodies withstand cold. The species is widespread across temperate and boreal North America, Europe and northern Asia, and is generally most frequent in cool, moist deciduous and mixed forest.

This is a saprotrophic white-rot fungus. Its mycelium decomposes lignin along with cellulose in fallen hardwood, leaving the wood pale, soft and fibrous. It usually arrives at a middle stage of decay, after pioneer colonisers have opened the bark and outer sapwood, and contributes to the gradual collapse of large logs into the forest floor.

Beyond decomposition, colonies of Lentinellus ursinus create structure on the surface of a log: the overlapping brackets trap moisture and litter, and the tough dried fruit bodies persist through winter as shelter for mites, springtails and small beetles. Within the Auriscalpiaceae, the species illustrates how the same lineage has produced gilled shelves, toothed fungi and coral-shaped fruit bodies from a shared ancestry.

Lentinellus vulpinus is the closest relative and shares the sawn gill edges, but it is generally paler and whiter, its base is drawn out into a tough, ridged, densely hairy pseudostipe, and its upper surface is more strongly wrinkled and furrowed; it also grows more often in dense fused clusters. Lentinellus micheneri and its allies have a distinct, if short, central to lateral stem and much smaller caps.

Panellus stipticus forms small tan shelves on hardwood but has a short distinct lateral stem and smooth-edged gills. Pleurotus and Hohenbuehelia species are stemless or nearly so with soft flesh and even, knife-edged gills, never toothed. Crepidotus species are soft, pale and thin-fleshed and drop a brown spore print instead of white.