Plums and Custard Identification Guide

First Impression and Setting

This is a stump-top species, and the setting narrows things down before you have looked at a single character. You are typically standing in a conifer plantation, a spruce or pine wood, or beside an old sawn stump on a forest track, and what stops you is the colour combination: a strongly yellow mushroom overlaid with dense wine-red, purple-brown or maroon wool. From several metres away it reads as a two-tone fungus, the red concentrated at the centre of the cap and breaking into scattered specks towards the rim, with yellow showing through everywhere between. Fruit bodies are usually solitary or in small loose groups of two or three, sitting directly on rotten conifer wood, occasionally apparently on soil where a buried root is decaying.

Reading the Cap

The cap is 4 to 12 cm across, occasionally larger, starting hemispherical with a strongly inrolled margin, then convex and finally flat, often with a low broad umbo. The surface is dry, never sticky, and the texture is the point: the underlying skin is bright yellow, and over it lies a coat of fine woolly to fibrillose scales in a deep purplish-red to brownish-crimson. At the centre these scales are dense and can merge into an almost uniform dark disc; outwards they separate into discrete tufts and radiating fibrils, so the yellow ground colour is exposed in a marbled or streaked pattern. On old, weathered or rain-washed material the scales fade towards brown and the cap can look duller, but a hand lens will still show the fibrillose overlay rather than a smooth cuticle. The margin is often minutely fringed with veil fibrils when young.

The Gills

Turn it over. The gills are the second half of the name and are hard to mistake: bright chrome to egg-yellow, crowded, moderately broad, and attached to the stipe in a sinuate or notched fashion, sometimes appearing simply adnate. There is no free gap around the stipe apex. Under a lens the gill edges are finely flocculose or minutely toothed, and in age they can pick up a faint rusty or reddish flush along the edge, particularly where handled. Short intermediate gills of two or three lengths run in among the full-length ones. Nothing about the gills darkens with maturing spores, which is a useful early hint about the spore colour.

The Stipe and Base

The stipe is 4 to 10 cm long and 1 to 2 cm thick, roughly cylindrical, often curved where it emerges from the vertical face of a stump, and sometimes slightly swollen or narrowed at the base. Its ground colour matches the gills, a clear yellow, and it is overlaid with reddish to purplish fibrils that are usually sparser than those of the cap and concentrated on the lower half. There is no ring, no ring zone worth the name, and no volva. Excavate the base carefully: it should be attached to wood, and you will often find yellowish mycelium and fine strands binding rotten conifer fibres together. Trace the attachment before you commit, because a stump can be almost completely buried under needle litter.

Flesh and Colour Change

Slice a fruit body from cap edge to stipe base. The flesh is pale yellow throughout, firm and slightly fibrous in the stipe, softer in the cap, and it does not change colour when cut or bruised beyond a slow, faint browning in the stipe base of old specimens. There is no milk, no latex, and no blueing. The absence of colour change is worth confirming, because several of the brown-spored wood-dwellers that share these stumps do discolour.

Taking a Spore Print

Cut the cap free at the top of the stipe, set it gills-down on a sheet of white or, better, half white and half dark paper, cover it with a bowl to hold humidity, and leave it for three to six hours. The deposit is white, sometimes with the faintest cream cast in a heavy print. Against dark paper the white print is unmistakable. This single test removes the majority of the yellow wood-dwelling look-alikes at a stroke, since most of them drop rusty, tobacco or purple-brown spores. Under the microscope the spores are small, smooth, broadly ellipsoid, and do not turn blue-grey in iodine.

Substrate, Season and Habit

This species is a wood decayer, restricted in practice to conifers: spruce and pine stumps and logs, buried conifer roots, and old sawdust or chip piles from softwood. It appears from midsummer through to late autumn, peaking after warm, wet spells, and it can fruit on the same stump for several years running. Fruit bodies emerge singly or in small tufts, rarely in dense clusters, and often from the cut surface or the side of a stump rather than from the ground beside it.

Telling It From Its Nearest Relatives

The closest relative is Tricholomopsis decora. It shares the yellow ground colour, the yellow crowded gills, the white spore print and the conifer wood habit, but its cap scales are dark olive-brown to blackish and fine rather than woolly and wine-red, and it is generally smaller with a more depressed centre. Colour of the scales, judged on fresh material, does the separation.

Other Yellow Wood Mushrooms

• Gymnopilus junonius forms dense clusters, usually on hardwood, with a tawny orange fibrillose cap, a distinct ring on the stipe, and a rusty orange-brown spore print that dusts the ring.
• Pholiota species have viscid, scaly caps and drop clay to rust-brown spores; their gills darken with age instead of staying chrome yellow.
• Hypholoma fasciculare grows in tight tufts on stumps with a smooth sulphur-yellow cap, gills passing from yellow through greenish to purple-brown, and a purple-brown spore print.
• Yellow-capped Tricholoma species grow from soil in mycorrhizal association with trees, never from wood, and lack any red fibrillose overlay.
• Armillaria species have a membranous ring, cream spores and honey-brown scaly caps, and typically swarm at the base of a trunk rather than sitting singly on a cut stump.

Field Checklist

On conifer wood; cap yellow beneath a dense coat of wine-red woolly scales; gills bright yellow, crowded, notched, not darkening; stipe yellow with reddish fibrils, no ring; flesh yellow and unchanging; spore print white; summer to late autumn.