Verdigris Agaric Identification Guide

An Unmistakable First Sighting

There is a very short list of mushrooms in temperate woodland that are genuinely blue-green, and that colour is what makes the first stage of this identification almost instantaneous. You are typically on a damp woodland path, a grassy ride, a mulched border or the margin of a conifer or mixed plantation, in autumn, after rain. Among the leaf litter sits a cap the colour of oxidised copper — a cool blue-green, glassy with slime, often with a scatter of white flecks around its rim.

Stand back and take in the whole fruit body before you touch it. The blue-green pigment normally extends down the stalk as well, so the mushroom is coloured throughout rather than just on top, and the stalk usually carries or has carried a ring. Older caps lose the blue from the centre outwards, fading through a dull yellowish-green to a straw or ochre disc while a blue-green band lingers at the rim. Knowing that fading sequence prevents you from writing off a faded specimen as a different species.

Reading the Cap

Caps run about two to eight centimetres across. They begin conical to bell-shaped or bluntly convex, then expand to broadly convex and finally flat, sometimes with a low central hump.

The surface is heavily viscid to downright slimy in wet weather, coated in a gelatinous layer that picks up leaf fragments and needles and that can be lifted away in strings if you draw a knife blade across it. Under the slime the colour is a verdigris blue-green when fresh. As the fungus dries or ages, the slime thins and the colour retreats.

The margin is important. In young and middle-aged caps it is decorated with white to pale cream, cottony or scaly veil remnants left behind as the partial veil tears, giving the rim a fringed or flecked appearance. These fragments wash off in heavy rain, so their absence does not disprove the identification, but their presence supports it.

The Gills

Underneath, the gills are adnate — attached broadly to the stalk, sometimes with a small notch, but not running down it. They are crowded and moderately broad.

Colour is a maturation sequence that you should read carefully. Young gills are pale, whitish to pale grey or faintly clay-coloured. As spores develop they darken through greyish-violet and purplish-brown to a deep date-brown or almost purple-black in the oldest caps. Because the spores mature unevenly, mature gills often look mottled, with darker and paler patches across the same face.

The edge is the character to check with a lens. In this species the gill edges remain distinctly whitish, sterile and finely fringed, standing out as a pale line against the darkening faces. That pale edge on dark gills is one of the most useful separators from its nearest relative.

The Stalk and Ring

The stalk is two to ten centimetres long, slender, roughly equal or slightly thickened towards the base, and hollow or narrowly stuffed inside.

Above the ring the stalk surface is smoother and paler. Below the ring it is blue-green like the cap, sticky in wet conditions, and clothed with rings and scattered patches of white cottony scales that stand out sharply against the blue ground. Those white flecks on a blue stalk are as diagnostic as the cap colour.

The ring itself is membranous and usually well formed when fresh, sitting fairly high on the stalk. It is often striate on its upper surface, and as spores drop onto it, it turns dark purple-brown, which makes it easier to see in older specimens. In some collections the ring collapses or is washed away, leaving only a ragged zone.

At the base, look for white mycelial cords binding litter and mulch. There is no volva and no basal cup.

Flesh and Colour Change

Slice a fruit body from cap to base. The flesh is whitish to pale blue-tinged directly beneath the cap cuticle, thin at the margin and thicker at the disc, and the stalk cavity is usually evident in mature material. There is no dramatic bruising reaction, no latex, and no rapid darkening on exposure. The odour is faint and mushroomy, sometimes a little earthy.

Taking and Reading a Spore Print

Remove the stalk cleanly, place the cap gills down on white paper, cover it, and leave for four to eight hours. Mature caps here deposit heavily and quickly.

The result should be a dark purple-brown to purplish-black powder. Read it dry and heaped, on white paper, in daylight, and compare it deliberately against a plain brown reference if you have one — the violet component is real but subtle in thin deposits. This print, combined with adnate gills, a ring, and a slimy blue-green cap, closes off almost every alternative.

Substrate, Season and Ecology

This is a litter and wood-debris saprotroph rather than a root partner. It fruits from soil rich in decaying organic matter: leaf litter and needle duff, woodland path edges and grassy rides, wood-chip mulch in parks and gardens, and the disturbed ground beside forestry tracks. Both broadleaved and coniferous woodland support it, and mulched urban beds are increasingly productive sites.

Season is late summer through autumn, sometimes into early winter in mild conditions. Fruit bodies appear singly, in scattered troops, or in loose clusters where a rich patch of buried debris is being worked. Ecologically the mycelium is decomposing lignin-rich fragments in the upper soil horizon, which is why mulching a bed can produce a flush within a season or two of the chips being laid.

Separating It From Look-alikes

Stropharia caerulea. The genuine problem species, and the two are routinely confused. Work through three characters. First, the gill edge: in S. caerulea the edge is concolorous with the face and not conspicuously white-fringed, whereas here it is a distinct pale line. Second, the ring: S. caerulea has a poorly developed, often evanescent ring that leaves only a fibrillose zone, while this species usually shows a proper membranous ring. Third, gill colour at maturity: S. caerulea tends towards a more chocolate or purple-brown without the darker date tones, and it fades from blue to a yellowish-ochre more thoroughly and earlier.

Stropharia pseudocyanea. Paler, more delicate, its blue-green washed with yellow tones and fading quickly to almost yellow-grey. Its ring is slight, and it has a distinctive peppery odour that this species lacks. It is a grassland species more often than a woodland one.

Clitocybe odora. The other conspicuously blue-green woodland agaric, and easily separated once you look underneath. Its cap is dry and matt rather than slimy, its gills are pale cream and decurrent rather than dark and adnate, it has no ring at all, its spore print is white, and it carries a strong aniseed odour.

Chlorociboria and other green wood-staining fungi produce tiny green cups on stained wood, not fleshy stalked agarics; the confusion is only ever at the level of colour in a photograph.

Field Checklist

Blue-green slimy cap, fading from the centre; white veil flecks on the cap margin; crowded adnate gills passing from pale to mottled purple-brown with a persistently white fringed edge; blue-green stalk sticky below a membranous ring and scattered with white cottony scales; hollow stalk; dark purple-brown spore print; litter, mulch or path-edge substrate in autumn.