Tiger's Eye

Tiger's Eye (Coltricia perennis) is a distinctive little polypore that grows from the ground rather than from visible wood and carries its pores on the underside of a neat, stalked, funnel-shaped cap. The concentric bands of rusty brown, cinnamon, ochre and silvery grey across that cap, catching the light like polished stone, are what give it its English name.

It belongs to the Hymenochaetaceae, the family of rusty-brown-fleshed fungi that also includes the Phellinus and Inonotus brackets, and like its relatives it has brown flesh that blackens in potassium hydroxide. Unlike most of them it is thin, small and stipitate, which makes it look more like a tough little mushroom than a bracket fungus.

Despite the species epithet, individual fruit bodies are annual; the name refers to how long the tough dried caps persist on the ground. Weathered specimens from a previous season are a common find on heathland paths, faded to grey but still holding their shape.

Cap

Thin, leathery and tough, 2-8 cm across, circular and shallowly to deeply funnel-shaped with a depressed centre. The surface is finely silky-velvety and strikingly zoned in concentric bands of rusty brown, cinnamon, ochre, tan and silvery grey, the bands narrowing towards the sharp, often wavy and slightly paler margin. Old caps fade to a more uniform greyish brown. Neighbouring caps sometimes fuse laterally.

Pores

The pore surface is greyish brown to rusty cinnamon, running down onto the top of the stalk. Pores are angular to slightly irregular, fairly large for the size of the fungus at about 2-4 per millimetre, and the tube layer is very shallow, generally under 2 mm.

Stipe

A distinct central stalk, 1-4 cm tall and 2-8 mm thick, coloured rusty to dark brown, velvety-tomentose, sometimes slightly swollen at the base and usually with soil and sand grains bound to it.

Flesh and spore print

The flesh is very thin, tough, corky-leathery and rusty brown throughout, blackening immediately in potassium hydroxide as expected for the family. The spore print is yellowish brown to ochre-brown.

Tiger's Eye fruits directly on soil, favouring poor, sandy, acidic ground: heathland, sandy banks, the compacted edges of forest tracks, gravel paths, old fire sites and disturbed ground within or beside conifer plantations. Pine is the most frequent associated tree, though it also occurs with spruce and occasionally on more mixed ground.

It is widespread across the Northern Hemisphere, common in northern and central Europe, boreal and montane North America and northern Asia. Fresh caps appear from midsummer through late autumn, and because the tissue is tough and weather-resistant, dried and bleached caps from earlier seasons often remain visible on the same paths for many months.

The ecological role of Coltricia perennis has been debated. It fruits on mineral soil with no wood in evidence, and its consistent association with pine and other conifers, together with isotopic and molecular evidence, indicates that it is at least partly ectomycorrhizal, forming a nutrient-exchange partnership with tree roots. Some authorities have treated it instead as a soil and litter saprotroph.

Whatever the precise relationship, it is characteristic of nutrient-poor, sandy and disturbed sites, and it is a notable coloniser of burnt ground, where it can be one of the first larger fungi to reappear after a fire. Its ability to fruit on bare compacted paths and fire scars makes it a familiar component of the pioneer fungal community of heath and plantation edges.

Coltricia cinnamomea is a close relative that is smaller and more delicate, with a shinier, silkier, more intensely cinnamon to rusty-orange cap that has a distinctly satiny sheen, and it is more often associated with hardwoods and clay banks. The zonation in Coltricia perennis is broader, duller and greyer.

Onnia tomentosa superficially resembles a large Tiger's Eye, but it is much bigger and thicker, more coarsely tomentose, often forms clustered or fused fruit bodies at the base of conifers, and grows attached to roots. Polyporus species such as Polyporus varius and Polyporus brumalis also have a central stalk, but their pore surfaces are white to cream, their spore prints are white, and their flesh is white rather than rusty brown. Finally, weathered Coltricia caps on paths can be mistaken for the tough zoned caps of Trametes brackets, but Trametes is laterally attached to wood, has white pores and never has a central stalk.