Green skinhead

Cap

Cap 3-9 cm, convex to broadly umbonate, smooth and dry to slightly viscid.

The defining feature is colour: fresh young caps are a striking blue-green to teal - a vivid verdigris hue unusual among gilled fungi.

The colour fades progressively to olive-green, yellowish-green and dull ochre as the cap dries and ages, so old specimens can look very different from fresh ones.

Gills

Gills adnate, moderately crowded, initially pale grey-violet to olive-tinged, turning rust-brown as spores ripen.

The rust-brown spore print is a critical diagnostic feature and should be confirmed on white paper.

Stem

Stem 5-12 cm, cylindrical to slightly clavate, fibrillose, whitish to pale olive, sometimes with a violet flush at the apex.

The cortina - the fine cobweb partial veil that marks all Cortinarius species - shows as delicate threads between cap margin and upper stem in young specimens; it collapses quickly and leaves rust-brown fibre remnants on the upper stem at maturity.

Orellanine-bearing Cortinarius species are among the most dangerous mushrooms in the world, not because of acute toxicity but because the poisoning masquerades as ordinary illness for days to weeks.

By the time renal failure is diagnosed, the window for effective intervention has often narrowed substantially.

The distinctive green colouration of C. austrovenetus may make it more attractive to curious collectors than drab brown webcaps, compounding the risk.

The lack of Australian case series data (due in part to the relatively recent formal description of the species) does not reduce the danger - all Australian Cortinarius species must be treated as carrying full orellanine-class risk.

There is no antidote; treatment is supportive and may include corticosteroids to reduce inflammation and renal replacement therapy.

Orellanine (and potentially related orelline and cortinarin compounds), a bipyridine-N-oxide nephrotoxin.

It acts as a selective toxin targeting proximal tubule cells of the kidney, where it generates reactive oxygen species and disrupts cellular metabolism, ultimately causing tubular necrosis.

The toxin is absorbed slowly from the gastrointestinal tract and accumulates in renal tissue, explaining the characteristic long delay before symptom onset.

Chemical analyses have confirmed orellanine in numerous Cortinarius species globally; the Australian Cortinarius complex is presumed to share this toxicological profile.

The defining clinical feature of orellanine poisoning is its exceptionally long latent period - typically 2 days to 3 weeks - during which the victim may feel entirely well or only experience mild nausea and headache.

When symptoms emerge they include:

• intense thirst
• excessive urination (then diminishing urine output as kidneys fail)
• nausea
• vomiting
• generalised fatigue
• headache
• a burning or painful sensation in the flanks and lower back corresponding to renal inflammation

Without treatment, progression leads to acute interstitial nephritis, acute tubular necrosis, and acute renal failure.

A significant proportion of documented cases in Europe have required long-term dialysis; some have required kidney transplantation.

Never eat any Cortinarius species from native Australian forest.

The genus is known to contain orellanine, a potent nephrotoxin, across many of its species; the Australian species complex has not been fully analysed but must be assumed to carry equivalent risk to the European deadly webcaps (C. orellanus, C. rubellus).

Orellanine is particularly insidious because of its extremely long latency period: victims may feel well or only mildly unwell for 2 days to 3 weeks after ingestion, during which time irreversible kidney damage is progressing.

If any Cortinarius ingestion is suspected, seek emergency medical attention immediately, even if the person feels well.

Contact the Australian Poisons Information Centre: 13 11 26.

Ectomycorrhizal with native southeastern Australian trees, growing in intimate partnership with:

• Eucalyptus roots in moist sclerophyll and montane forest
• Nothofagus cunninghamii in cool temperate rainforest

The range covers the ranges of Victoria (Central Highlands, Otways, alpine foothills), Tasmania, parts of southern New South Wales and the ACT.

Appears singly or in loose scatter on the forest floor, nestled in deep leaf litter and duff beneath mature host trees on moist, loamy soils.

Southern Hemisphere autumn and early winter, March through June, with fruiting most reliable in April and May.

Fruiting bodies emerge after significant autumn rainfall once soil temperatures drop into the 8-14 °C range typical of the southeast Australian highlands - a fungus that waits out the dry summer underground and re-emerges when the cool rains finally arrive.

Obligate ectomycorrhizal partner of host trees; cannot grow without a living root network.

Forms intimate associations with Eucalyptus and Nothofagus roots in undisturbed or lightly disturbed native forest.

Fruiting bodies appear singly or in loose small groups, not in dense clusters.

The mycelium persists perennially and produces sporocarps each autumn when conditions are suitable.

Fruits in Southern Hemisphere autumn after meaningful rain events once soil temperatures fall into the 8-15 °C range. Conservative estimates derived from the known April-May peak season and standard Cortinarius ecology in southeastern Australian montane and moist sclerophyll forest.

The vivid green cap makes fresh specimens distinctive among Australian Cortinarius species, but faded or dried specimens become olive or ochre and may resemble other brownish webcaps.

Several other Cortinarius species occur in the same habitats and share the rust-brown spore print and cortina remnants - all should be treated as equally dangerous.

Greenish-capped species from other genera that might cause confusion include:

• Stropharia aeruginosa (verdigris roundhead) - a moist, slimy cap with greenish scaly veil remnants, but a dark purple-brown spore print and lacks a cortina.
• Certain Pholiota species - a scaly-slimy cap and ring but a similarly rusty spore print; however Pholiota grows on wood, not on soil in forest.

The rust-brown spore print and cobweb cortina remnants of Cortinarius are the definitive differentiating features.