Netted Fieldcap

The Netted Fieldcap, Bolbitius reticulatus, is the most distinctive member of its genus in temperate woodland, and one of the few Bolbitius species to grow on wood rather than on dung or grass. Its cap is covered in a slippery gelatinous layer beneath which a raised network of veins and wrinkles shows through, giving the surface a curiously embossed, reticulate look that no other common agaric matches.

Bolbitius sits in the Bolbitiaceae alongside Conocybe, Pholiotina and Agrocybe, all sharing a rusty to brown spore print and, in the more delicate genera, extremely thin and short-lived flesh. Fieldcaps are notorious for collapsing within a day, and this species is no exception.

Colour is another draw: young caps often carry an unusual violet, lilac or greyish-purple flush that fades to dull grey-brown as the fungus ages and the gills fill with rusty spores. Some authors treat the more strongly lilac forms as a separate variety.

Cap

The cap is 1.5 to 5 cm across, convex to broadly bell-shaped and then flattening, often becoming shallowly upturned at the edge before collapsing. The surface is coated in a distinctly viscid to slimy, translucent gelatinous layer, through which a raised network of anastomosing veins and radial wrinkles is visible, strongest over the disc. Colour is greyish, often with a violet, lilac or pinkish-purple tinge when fresh, becoming ochre-grey or dingy brown with age; the margin is thin and translucently striate.

Gills

Gills are adnexed to nearly free, crowded, thin and rather narrow, pale grey or whitish at first and colouring to cinnamon or rusty brown as spores ripen. They are soft and fragile and may partly collapse as the cap deliquesces slightly at maturity.

Stipe

The stipe is slender and fragile, 3 to 7 cm long and 1 to 4 mm thick, cylindrical or slightly tapering upward, hollow and whitish to pale cream. The surface is finely pruinose or minutely floccose, especially near the apex. There is no ring and no volva, and the base may be attached to a small pad of white mycelium in the wood.

Flesh and spore print

The flesh is extremely thin, watery and pallid, without notable colour change when cut. The spore print is rusty brown to ochre-brown. Microscopically the spores are smooth, ellipsoid to almond-shaped with a truncate germ pore, and the cap cuticle is a gelatinised layer that accounts for the slimy feel.

This fieldcap grows on damp, well-rotted wood of broadleaved trees, with beech a particular favourite, and also on ash, elm, sycamore, poplar and other hardwoods. It is found on fallen logs, large branches lying in leaf litter, cut stumps and sawn timber, generally where the wood has softened and stays moist under shade.

Fruit bodies are produced singly or in small scattered groups, often in the mossy or damp shaded parts of a log, and appear from midsummer through autumn, especially after prolonged damp weather. The species is widespread but rarely abundant across Europe and temperate North America and occurs in temperate deciduous woodland elsewhere.

Bolbitius reticulatus is a saprotroph of decaying hardwood, its mycelium working through the softened, already partly decomposed tissue of logs and stumps. It tends to appear in the later stages of decay rather than on freshly fallen wood, taking advantage of material already broken down by earlier colonisers.

The gelatinised cap surface is thought to help the very thin fruit body hold moisture long enough to mature, in a genus otherwise renowned for evaporating within hours. Even so, the fruiting cycle is compressed: caps expand, colour up with rusty spores and slump within a day or two, releasing spores into the humid air of the woodland floor.

Bolbitius titubans, the Yellow Fieldcap, is the commonest relative and shares the slimy cap and rusty print, but it is bright egg-yellow when young, lacks any reticulate veining, and grows in grass, dung and mulch rather than on logs. Pluteus species on logs can be similar in stature but have free gills that turn pink and a pink spore print, plus a firmer stipe.

Conocybe and Pholiotina species have dry rather than slimy caps and mostly grow in soil or mulch, and they lack the raised network entirely. Psathyrella species on rotten wood are brittle with a blackish-brown print and no gelatinous layer. In practice, a slimy grey-lilac cap with a visibly veined, embossed surface on a rotten hardwood log is diagnostic.