Shingled Hedgehog

The Shingled Hedgehog is the best-known member of Sarcodon, a genus of substantial ground-dwelling toothed fungi. Its cap can reach the size of a dinner plate and is covered with big, coarse, dark scales that lift at their edges, arranged in rough concentric rings so that the surface resembles overlapping tiles or the feathering of a hawk's wing, which explains both of its widely used common names.

Sarcodon belongs to the Thelephorales, the order containing the stipitate hydnoid fungi and the leathery Thelephora species. Members of this order characteristically produce brown, warted spores, and this is the single most useful laboratory-free distinction between Sarcodon and the white-spored Hydnum hedgehogs, which look superficially similar in outline but not in texture or colour.

The species is a classic component of old conifer forest on poor sandy ground. Its populations have declined across much of Europe with nitrogen enrichment and forest management change, and stipitate hydnoids as a group are now closely tracked as indicators of undisturbed, nutrient-poor woodland soils.

Cap

Large, commonly 5-20 cm and occasionally to 30 cm across, at first convex and soon flat with a distinctly depressed or funnel-shaped centre. The ground colour is pale to mid brown, overlaid with conspicuous coarse dark brown to blackish-brown scales that are broad, often upturned at the tips and arranged in rough concentric zones. The scales are largest and most raised near the centre and flatten toward the margin.

Spines

The underside is packed with crowded, slender, pointed spines 5-10 mm long that run a short way down the stalk. They start pale greyish-white and darken through grey-brown to a deep purplish-brown as spores mature, giving the underside a much darker cast in old specimens.

Stipe

Short and stout in proportion to the cap, 3-8 cm tall and 1.5-3 cm thick, more or less cylindrical or slightly tapering downward, dry and smooth to slightly felted, pale brown and often darker or greyish toward the base.

Flesh and spore print

The flesh is thick, firm and whitish to pale grey-brown, sometimes discolouring greyish or brownish when cut, and it is fleshy rather than corky, distinguishing Sarcodon from the woody Hydnellum species. The spore print is brown; the spores are pale brown, angular and coarsely warted or tuberculate under magnification.

The Shingled Hedgehog is a ground fungus of coniferous woodland, especially mature spruce and pine growing on sandy, acidic, nutrient-poor soils. It fruits among needle litter and moss, often in scattered troops, arcs or loose rings, and shows a strong preference for old stands that have not been fertilised or heavily disturbed. Sandy heathland pine and northern spruce forest are prime habitat.

Fruiting occurs from late summer into autumn. The species occurs widely across boreal and temperate Europe and northern Asia, and closely related scaly Sarcodon species occur in North America. Modern study has split the traditional broad concept of S. imbricatus, with spruce-associated and pine-associated populations now often treated as separate species.

This is an ectomycorrhizal fungus. Its mycelium forms sheaths around the short roots of conifer partners, principally spruce and pine, and exchanges mineral nutrients and water drawn from a large soil volume for photosynthetic sugars supplied by the tree. This partnership is what allows conifers to thrive on the impoverished sandy soils where the fungus is most often found.

Colonies are long-lived and expand slowly through the soil, so fruiting bodies return to the same locations over many years. The group is highly sensitive to nitrogen deposition and to soil disturbance, and stipitate hydnoids including this species are used across Europe as indicators of forest continuity. Fallen fruiting bodies are also colonised by a distinct community of beetles and fly larvae in the litter layer.

Sarcodon squamosus is extremely close and was long lumped with this species; it associates with pine on dry sandy ground and generally has smaller, flatter, less strongly upturned scales and a somewhat darker overall tone. Sarcodon scabrosus has a scaly brown cap too but shows a distinctly blue-green to blackish stain in the base of the stalk when it is sliced lengthwise, a decisive character.

Hydnellum species share the brown spore print and toothed underside but have thin, tough, corky to woody flesh that is concentrically zoned in section and caps that are felted, lumpy or fused rather than covered in large lifting scales. The Hydnum hedgehogs are unscaled, pale cream to orange, with brittle white-spored flesh, so a brown spore print alone rules them out.