Recognizing Cortinarius, our most common enemy

Mushrooms of the genus Cortinarius are a common sight on any foray in the Arizona monsoon season.  Many of them are toxic, and very few are edible.  The genus is enormously large and poorly described. From an edible mushroom forager’s point of view, identifying the genus is critically important but relatively easy, while identifying the individual species is highly challenging but ultimately irrelevant.

faint cortina cortinarius

Cortinarius does not have quite the same fearsome reputation as the deadly members of the genus Amanita such as A. ocreata, the Western Destroying Angel.  However, they are far more common, and can cause death or serious permanent disability by being mistaken for certain edible species.  The most famous victim of Cortinarius poisoning is undoubtedly Nicholas Evans, author of the book The Horse Whisperer, who almost killed himself and members of his family by serving them C. speciosissimus he somehow managed to mistake for king boletes.  He is now on dialysis and awaiting a kidney transplant.

The damage caused by Cortinarius results from orellanine, a chemical compound that results in a tubulointerstitial nephritis of the kidney. This can lead to complete and irreversible renal failure that is lethal unless the patient receives a renal transplant or undergoes hemodialysis for the rest of his or her life. The symptoms can take a considerable time to appear, often manifesting as a flu-like syndrome 2 or 3 days after ingestion.  Full-blown renal failure may not occur for weeks thereafter.

Identification of these mushrooms usually depends on two characteristics: the presence of a cortina, a wispy fibrillose remnant of the partial veil; and a rusty brown spore print.  The cortina is quite prominent in immature fruiting bodies, when it forms the intact partial veil that is still covering the gills.  It will often show fibrous whitish strands that can resemble cotton, glue, or mucus, depending on how dry they are.  As the mushroom ages, the cortina becomes fainter, darker, dryer, and more threadlike, appearing as a frangible cobweb encircling the upper part of the stem.  It is typically of a brownish color.   Careful inspection is usually necessary to see these features in mature mushrooms, and it should be kept in mind that the cortina can involute to leave only an indistinct “ring zone”, or may disappear entirely.

The images below show Cortinarius specimens typical for Arizona at various stages of development.  Take particular note of the white, cottony partial veil evolving to a rust-colored cobwebby cortina, and then to a brown ring zone with only the faintest remnant of a cortina.

Of particular interest, the following comparison images show how easily an immature Cortinarius can be mistaken for an aspen bolete, Leccinum insigne, in its young button stage. These mushrooms were picked about 50 feet apart on the same day.  Note the bare stem and intact partial veil covering the gills in the immature Cortinarius, contrasted with the pores on the hymenial undersurface of the cap of the Leccinum, as well as the speckled appearance of the scabers on its stipe. Any apparent “scabers” on the stem of the Cortinarius are merely flecks of dirt.

Keep your eyes open for these!  If you get greedy or rushed when you find a large flush of aspen boletes, you could end up with one of these orange-capped troublemakers in your basket.

But the Cortinarius genus is not altogether worthless. If you are interested in natural fabric dyes, the reds, browns, and yellows produced by various members of the Cortinarius genus will make it one of your best friends rather than your mortal enemy.

About Christopher May

Chris is a radiologist in private practice in Scottsdale. He is married to Barbara May, with two grown children, Megan and Nick.
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