Netted Fieldcap Identification Guide

The First Impression

The netted fieldcap is a fungus you find by accident, usually while looking at something else. You are crouched over a mossy fallen beech trunk after a warm rain, and there on the bark is a small, wet-looking cap in an odd grey-lilac shade, mounted on a stem so thin and white it looks like a bristle. Touch it clumsily and it collapses. Bolbitius reticulatus is one of the most fragile of all the wood-dwelling agarics, and it is gone within a day or two of appearing.

The setting is damp, shaded deciduous woodland: beech, elm, willow, poplar, ash, sycamore. It fruits singly or in small scattered groups on decaying trunks, stumps, fallen branches and occasionally on wood chips in shaded corners of parks and gardens.

Reading the Cap

Cap width is small: 1.5 to 5 cm, usually toward the lower end. The shape opens from hemispherical or bluntly conical through convex to nearly plane, often keeping a low broad umbo, and the margin frequently splits or turns up in age.

Colour is the first thing that marks it out. Young caps are grey to grey-brown with a clear violaceous, lilac or purplish grey wash, strongest over the disc. As the cap expands and dries, the lilac tones drain away toward dull ochre-buff, clay or plain grey, so an old cap is far less distinctive than a fresh one. Photograph young material.

Two surface characters matter. First, the cap is viscid to frankly glutinous when moist, coated in a slippery film that dries to a shine. Second, and this is the character in the name, the disc carries a pattern of raised, branching, interconnecting veins and wrinkles that form a low network, a reticulum, across the centre. It is easiest to see when the cap is wet and lit obliquely: tilt the cap so light rakes across the surface and the mesh of ridges stands out. The outer part of the cap is instead translucent-striate, with the gill lines showing as dark radiating streaks through the paper-thin flesh, sometimes to half the radius or more.

Gills

Turn the cap over gently. The gills are adnexed to almost free, moderately crowded, ventricose, and rather broad relative to the tiny cap.

Colour development is important and rapid. They start pale grey to cream, pass through dull clay and cinnamon, and finish a distinctly rusty ochre-brown as the spore load matures. Gill edges are paler, minutely floccose or fringed under a lens.

The gills soften and can become slightly gelatinised as the fruit body collapses, but they do not dissolve into black ink. That single observation separates this fungus from the inkcaps that share the same wood.

Stipe, Base and Flesh

The stipe is 3 to 7 cm long and only 2 to 5 mm thick, cylindrical or very slightly swollen at the base, hollow, straight or slightly curved, and extremely brittle. It snaps rather than bends.

Colour is white to pale cream, sometimes slightly yellowish or greyish downward, and there is no ring. The whole length is finely pruinose to floccose, coated in minute white powdery granules or fibrils that are densest at the apex and easily rubbed off. Use a lens; this pruinosity is a genuine character rather than dew.

The base is not bulbous and has no volva, and it is usually attached to the wood by a small pad of white mycelium.

Cut the fruit body in half lengthways. Flesh is very thin, whitish to watery grey, soft and hygrophanous in the cap, and it shows no colour change on cutting or bruising. Nothing reddens, blues or blackens.

Taking a Spore Print

This species matures so quickly that prints are easy, provided you act while the cap is still standing. Cut the stipe flush and set the cap gills down on white paper, cover with a cup, and check after two to four hours. Use white paper rather than black, since the print is a mid-toned rusty brown that reads poorly against dark card.

The print is rusty ochre to cinnamon-brown. Under the microscope the spores are large for such a small mushroom, roughly 10 to 14 by 6 to 8 micrometres, smooth, thick-walled, honey to rust-brown in water, ellipsoid, and with a broad truncate germ pore at the apex. The gill face carries broadly clavate to sphaeropedunculate cells, and the cap cuticle is a cellular hymeniderm, both typical of the Bolbitius and Conocybe group.

Substrate and Season

The fungus is a wood decomposer, tied to well-rotted deciduous timber that is damp and often mossy. Beech and elm are frequently cited, but willow, poplar, ash and other broadleaves all serve, and it appears on fallen trunks, standing dead wood, old stumps and sometimes buried wood and chip mulch.

Season is late spring through autumn, with fruiting following warm humid weather and rain. Because individual fruit bodies last barely 48 hours, repeated visits to a promising log during a wet spell are far more productive than a single search.

Separating the Look-Alikes on Morphology

Bolbitius titubans. The common yellow fieldcap. It is bright egg-yellow at the disc, extremely slimy, and it grows on grass, dung, straw and rich mulch, not on rotten logs. It has no reticulate disc and no lilac tones.

Bolbitius variicolor. Larger and variegated in yellow, olive, brown and grey, growing on nutrient-rich soil and mulch rather than on decaying trunks.

Pluteus species. Many small Pluteus fruit on the same rotting logs and can look similar in size and stature. Their gills are truly free and turn pink, and the spore print is pink. That is the fastest split available.

Psathyrella and Coprinellus species. Also wood-associated and equally brittle, but their spore prints are dark brown to blackish. Coprinellus species often have pleated caps with granular or mealy veil remnants and frequently deliquesce.

Conocybe and Pholiotina. Share the rusty print, the truncate germ pore and the cellular cap cuticle, so microscopically they sit close by. In the field they differ clearly: caps are dry, conical to bell-shaped, ochre to tan, never lilac-grey, never netted, and they grow on lawns, soil and mulch rather than on rotten wood.

Simocybe centunculus. A small brown wood agaric with a dull olive-brown, dry, finely velvety cap and a brown print, but with no gluten, no reticulation and no violet tones.

Tubaria species. Brown, dry, hygrophanous caps with pale veil fibrils at the margin, on woodchips and litter, lacking a netted disc.

The combination that settles it is: rotten deciduous wood, a small viscid grey-lilac cap with a raised network of veins over the disc and a translucent-striate margin, adnexed gills turning rusty, a fragile pruinose white stem with no ring, and a rusty brown print of large truncate-pored spores.