Resinous Polypore

The Resinous Polypore (Ischnoderma resinosum) is a large, handsome autumn bracket of hardwood forests, appearing late in the season when most other fleshy fungi are finishing. Young fruit bodies are soft, watery and remarkably plush to the touch, with a thick rounded white margin that contrasts strongly against the deepening reddish brown of the older cap.

The genus name refers to the tough, thin crust that develops on the cap as the bracket ages and dries, while the species epithet describes the amber resinous droplets that bead on the upper surface and margin of actively growing specimens in humid weather. Both characters are useful in the field.

Ischnoderma belongs to the Fomitopsidaceae in the broad sense and contains a small number of similar species that differ largely in host preference. In North America and Europe it is a familiar sight on well-rotted logs of beech, maple and oak, where its shelving tiers can be half a metre wide in total.

Cap

Annual, broadly attached and shelf-like, 8-25 cm across and 1-3 cm thick, often several brackets fused side by side into a wide undulating shelf. The surface is finely velvety at first, soft to the touch, and coloured pale tan to orange-brown, darkening to deep reddish brown and finally almost blackish brown from the base outward. Actively growing brackets have a broad, blunt, white to cream margin and frequently exude clear amber droplets. With age the surface becomes smooth, faintly zoned and develops a thin varnished crust.

Pores

The pore surface is white to cream when fresh, bruising and ageing to dull brown or greyish brown where touched. Pores are small and round, roughly 4-6 per millimetre, giving an almost smooth appearance. The tube layer is shallow, generally 3-8 mm deep, and clearly delimited from the flesh above.

Flesh and spore print

Fresh flesh is soft, watery, fibrous and whitish to pale buff, drying much firmer and corky with a brownish tinge. Young specimens are heavy with moisture and can be squeezed like a sponge. Many collections carry a pleasantly aromatic scent. The spore print is white.

The Resinous Polypore fruits on dead hardwood, favouring well-decayed logs, large fallen limbs and stumps of beech, maple, oak, birch and other broadleaved trees in moist deciduous and mixed woodland. It is a wood-inhabiting species and is not found on soil, although brackets on buried wood can appear to arise from the ground.

It is widely distributed across temperate North America and Europe, extending into eastern Asia. Fruiting is strongly seasonal and late, with most collections made from early autumn until the first hard frosts, which is why it is sometimes called the late fall polypore. Old blackened brackets persist on the log through winter.

This is a white-rot saprotroph. Its enzymes break down lignin along with cellulose, and wood in an advanced stage of colonisation becomes pale, soft, stringy and light. It is generally a mid to late stage decomposer, arriving on logs that have already lost their bark and been opened up by earlier colonisers.

By converting large-diameter hardwood into soft, water-retentive material, Ischnoderma creates habitat for invertebrates, mosses and the seedlings that root on nurse logs. The bracket itself is a nursery for fungus gnats and beetles, and the persistent dried fruit bodies remain on logs long after spore release, continuing to shelter small invertebrates through winter.

Ischnoderma benzoinum is nearly identical but fruits on conifer wood and tends to be darker with a more strongly zoned cap and a duller, more greyish tone; host is the practical separator. The Dyer's Polypore (Phaeolus schweinitzii) is also velvety and brown but is normally attached to conifer roots or the base of conifer trunks, has a bright yellow-green margin when young, and a coarse, angular, greenish-yellow pore surface rather than fine white pores.

Young Ganoderma brackets can look similar in colour, but they quickly develop a hard, lacquered or dull crust and their pore surface bruises distinctly darker brown; their flesh is firm and fibrous rather than watery. Fomitopsis species have hard, banded, crusted caps from the outset and never show the soft velvety texture or the thick white droplet-bearing margin of the Resinous Polypore.