Wrinkled Peach

Rhodotus palmatus is the only species in its genus and one of the most immediately recognisable fungi in temperate woodland. The cap is thick, gelatinous-rubbery and coloured in shades of apricot, peach, salmon and rose, and its surface is raised into a network of pale ridges and pits like veining pressed into wax. Nothing else of comparable size and habit looks remotely like it.

The genus is placed in the Physalacriaceae, the family that also contains the Porcelain Fungus and the honey fungi, though Rhodotus stands well apart from its relatives in appearance. Its pinkish spore print once encouraged comparison with the shield mushrooms, but its gills are attached rather than free, and its tough gelatinous flesh, eccentric stem and reticulate cap are unlike anything in Pluteus.

Many populations are tied to elm, and the species became conspicuous in parts of Europe during the waves of Dutch elm disease, when huge quantities of dead elm wood became available. As that resource has aged and diminished the fungus has become less frequently reported in some regions, and it is treated as a species of conservation interest in several European countries.

Cap

2-6 cm across, occasionally to 10 cm, convex with a strongly inrolled margin when young, expanding to broadly convex or kidney-shaped. The colour is apricot, peach, salmon-pink, rosy or occasionally pale orange, fading with age and in strong light. The surface is gelatinous, rubbery and slightly translucent, and is raised into a distinctive network of paler cream to pink ridges enclosing shallow pits, so it looks embossed or veined. Young caps often exude drops of orange-red liquid.

Gills

Pale pink to salmon or flesh-coloured, moderately spaced, fairly broad, and attached to the stem, sometimes with a slight notch or a short decurrent line. Cross-veins frequently connect the gills near the stem, and the edges are even.

Stipe

1.5-6 cm long and 0.4-1.2 cm thick, usually eccentric or lateral and often curved, since the mushroom grows sideways from a log. It is whitish to pale pink, sometimes tinged apricot, smooth to finely fibrillose, with no ring, and may be slightly swollen at the base.

Flesh and spore print

The flesh is pinkish-white, thick, notably elastic and rubbery, and does not readily break. The spore print is pinkish to salmon-buff; spores are round and ornamented with warts, another feature setting the genus apart from the smooth-spored shield mushrooms.

Rhodotus palmatus fruits on dead hardwood, most characteristically elm, and also on ash, maple, sycamore, lime, horse chestnut, beech and poplar. It favours large fallen trunks, stumps and thick branches in damp, deeply shaded situations, often on wood that is already well decayed, moss-covered and lying directly on wet ground. Fruit bodies commonly emerge from the shaded underside or the sheltered flanks of a log rather than the exposed upper surface.

The season is late, running from late summer through autumn and often into early winter, with fruit bodies tolerating cool weather. The species is distributed across temperate Europe, temperate North America and parts of temperate Asia including Japan and Korea, but it is patchily distributed and locally uncommon, and its populations have fluctuated with the availability of dead elm.

This is a saprotrophic white-rot fungus of large-diameter hardwood. Its mycelium degrades lignin and cellulose in trunks and stumps that are already at a moderate to advanced stage of decay, contributing to the final breakdown of heavy timber into soft, pale, crumbling material that merges with the soil.

Because it depends on substantial pieces of dead hardwood in humid, shaded, undisturbed conditions, Rhodotus palmatus is a good indicator of woodland with continuity of deadwood. Sites that are tidied of fallen trunks lose it quickly. Its highly gelatinous flesh helps it retain water in the airless microclimate beneath logs, and the striking pigmentation and reticulate surface, unique among European agarics, have made it a favourite subject for photographers and a flagship species for deadwood conservation.

There is no close look-alike among temperate agarics once the raised cap network and rubbery flesh are seen. Pink oyster mushrooms, Pleurotus djamor, share the pink tones and lateral stem but have smooth, thin, fan-shaped caps without any reticulation and decurrent gills. Rhodocollybia species are pinkish-brown but have dry, smooth caps and central stems, and grow from litter rather than sideways out of logs.

Young Pluteus species may show pinkish gills and a pink print, but their gills are entirely free from the stem, their flesh is soft and fragile rather than elastic, and their caps are never veined. Panus neostrigosus grows in similar places and has a lateral stem, but is coarsely hairy, tough and tan to rusty rather than smooth, gelatinous and apricot.