Pluteus thomsonii

Pluteus thomsonii, the Veined Shield, is a small woodland species whose cap looks as though it has been embossed. A network of raised, paler veins and ridges runs across a darker grey-brown to sepia surface, and in well-developed specimens these ridges continue down the stipe as fine longitudinal lines — a feature almost unique in the genus.

It belongs to the group of Pluteus species with a cellular cap cuticle, sharing that structure with the yellow and wrinkled shields, but its muted grey-brown colouring sets it apart from them. It is a small fungus, easily passed over in leaf litter, and most records come from mycologists deliberately searching fallen twigs and small branches in damp woodland.

The species is named for the British mycologist Peter Thomson. Older literature sometimes treats it within a broader concept of the veined shields, but the combination of small size, grey-brown reticulate cap and ridged stem apex is distinctive enough to recognise consistently in the field.

Cap

The cap is small, 1–3.5 cm across, convex and often flattening with a slightly depressed centre. The ground colour is grey-brown, sepia, dark mouse-brown or almost blackish over the disc, becoming paler towards the margin. Across this surface runs a conspicuous network of raised, paler veins and ridges — the most distinctive feature — forming an irregular reticulum strongest over the centre. The margin is thin and may be faintly striate when moist.

Gills

The gills are free from the stipe, moderately crowded, fairly broad, white to greyish when young and turning salmon-pink at maturity. Gill edges are even and remain pale.

Stipe

The stipe is 2–5 cm tall and 2–4 mm thick, slender, greyish to pale brown, and finely pruinose or minutely powdery, especially towards the apex. In many specimens fine longitudinal ridges or veins run down the upper part of the stem, appearing to continue the cap reticulum. There is no ring and no volva.

Flesh and spore print

The flesh is thin, whitish to greyish, and does not change colour when cut. The spore print is pink to salmon-pink; spores are smooth and broadly ellipsoid to subglobose. The cap cuticle is composed of rounded to pear-shaped cells, and the pleurocystidia are thin-walled without apical hooks.

Veined Shield fruits on decaying hardwood, particularly small material: fallen twigs, branch fragments, buried sticks and the softened wood of small logs, usually well embedded in damp leaf litter. Beech, ash, hazel, elm and other broadleaves are typical, and the species favours shaded, humid woodland where the litter layer stays moist through the summer.

The season runs from summer into autumn. Fruit bodies are small and scattered rather than clustered, and because they sit close to the ground among leaves they are easily overlooked. The species is recorded across temperate Europe, including Britain and Ireland, with scattered records from other parts of the Northern Hemisphere.

The fungus is saprotrophic and causes white rot in fine-diameter hardwood. Its ecological niche is the twig-and-branch fraction of the woodland floor, an abundant but rapidly cycled resource, and the mycelium spreads through this scattered material rather than occupying a single large log.

Fruiting depends on humidity, since the thin-fleshed caps dry out quickly, so it is most reliably found in shaded valleys, stream margins and dense woodland after rain. Spores discharged from the free gills are dispersed by air movement close to the ground and by disturbance of the litter layer by animals and weather.

Wrinkled Shield (Pluteus phlebophorus) is the closest relative in appearance: it also has a veined cap but is larger, warmer reddish-brown to date-brown, and has a smooth whitish stem without the fine ridging and pruinose surface of P. thomsonii. Velvet Shield (Pluteus umbrosus) is much larger, has dark scales along the veins and a dark brown fringed gill edge. Goldleaf Shield (Pluteus romellii) shares the small size and wrinkled cap but has a bright chrome-yellow stem.

Small grey-brown Entoloma species can look similar but their gills are attached to the stipe, their spores are angular, and they fruit from soil. Small grey Mycena species on twigs have attached gills, a white spore print and a much more fragile, often bleeding or watery stem.