Webcaps: how to recognize the genus and why to leave them be

A webcap (genus Cortinarius) isn't hard to recognize as a genus: young mushrooms have a thin, cobweb-like veil over the gills, the spore print is rusty brown, and rusty threads are left behind on the stem. The trouble lies elsewhere. There are thousands of webcaps, and even a specialist often can't name the species without a microscope. Among them are deadly poisonous species containing orellanine, which destroys the kidneys after a delay of one to two weeks. So our rule is simple: we photograph webcaps, but they don't go in the basket. The one exception worth knowing is the gypsy mushroom.

The cover shows a large webcap we found in a birch wood in early October 2026. Below, we explain what you can see on it and why we can't name even a mushroom this handsome to species.

Three signs that give a webcap away

Webcaps are gilled mushrooms that live in partnership with tree roots, so they only grow where there are trees. They vary hugely in size and color, from small rusty ones to large violet ones, but they all share the features of the genus.

• The cortina. In a young mushroom, a thin veil much like a cobweb stretches between the cap edge and the stem. That's where the genus gets its name. When the cap opens, the cortina tears: some of the threads disappear, and some settle on the stem as a thin band.
• Rusty-brown spore print. This is why the gills of mature webcaps turn brown, even if they were yellowish, violet or ochre when young.
• A rusty band on the stem. Spores settle on what's left of the cortina, leaving a rusty “cobweb” on the stem. It's a handy sign, because you don't have to pick the mushroom and take a spore print.

Together these three features say “this is a webcap”. From here on, though, things get much harder for the forager.

Our webcap: handsome, large and nameless

The mushroom on the cover really is striking: a gray-brown cap covered in small scales, and a thick stem with a club-shaped swelling at the base. Seen from above, the cap is convex, with a small notch at the edge. It was growing alone beside an old rotting log, among fallen birch leaves.

When we lifted the mushroom, the most interesting part came into view: the stem base and the mycelium in the soil were lilac-violet, and so were the gills under the cap. Our first thought was the violet webcap. But that species is violet all over, cap included, while this cap is brown. A second look showed it's a different webcap, most likely from the scaly webcap (C. pholideus) group or the variable webcap (C. anomalus) group. Both have violet-tinged gills when young, both grow under birches, and field guides consider both inedible.

Why don't we give an exact name? Because these groups contain species that look alike, and a reliable identification needs a microscope and young mushrooms that still show the original gill color. From a photo of a mature mushroom, it's only a guess. We've described what the real violet webcap looks like, and how we ourselves got this mushroom wrong at first, in the article violet webcap in photos.

Why you can't identify a webcap from a photo

Webcaps are the largest genus of gilled mushrooms in the world. Mycologists put it at thousands of species. In 2022 a large team of researchers, working from genome analysis, even split the old genus into ten separate genera, and a great many species still remain in Cortinarius itself. Michael Kuo of MushroomExpert frankly calls identifying webcaps to species a quixotic undertaking.

What this means for the forager:

• Cap color changes with age, after rain and in the sun. An old, faded mushroom may look nothing like its own portrait in a field guide.
• Many species differ only in the size and shape of their spores under the microscope.
• A phone photo, however sharp, can't show the smell, the microscopy or the color of the young gills.

So when someone in a foraging group looks at a photo and confidently says “this is an edible webcap”, be wary. We don't allow ourselves that kind of call either.

Deadly webcaps and orellanine

The most dangerous members of the genus are the fool's webcap (Cortinarius orellanus) and the deadly webcap (Cortinarius rubellus, synonym C. speciosissimus). Both are medium-sized mushrooms with a dry, rusty-orange or rusty-brown cap 4–8 cm across, often with a small bump in the center, and yellowish gills that turn rusty with age. The first grows mainly under broadleaved trees, especially oak; the second in damp conifer forests under pine and spruce, on acid soils. The deadly webcap often has yellowish bands across the stem, like a snakeskin pattern.

Both contain orellanine, a toxin that selectively attacks the kidneys. What makes it so dangerous, above all, is how treacherous it is:

• A long quiet period. According to a review of 90 described poisonings (Danel et al., 2001), digestive upset usually appeared only on the third day, and signs of kidney damage usually on the eighth or ninth. Sometimes the quiet period lasts one to two weeks, rarely even longer. By then, people no longer link feeling unwell to mushrooms they ate so long ago.
• Severe consequences. In the same review, acute kidney failure became chronic in roughly half of the cases. In a Swedish study of 28 people poisoned by the deadly webcap, 22 needed dialysis and 15 later received a kidney transplant.
• Cooking doesn't help. Cooking, drying and freezing don't destroy orellanine. Boiling and pouring off the water reduces some other mushroom toxins, but don't count on it to deal with orellanine: there's no evidence that it removes it.
• There is no specific antidote. Treatment means supporting the kidneys, and dialysis.

The toxicity of the fool's webcap was first established in the 1950s, after a mass poisoning in Poland. In Sweden, the deadly webcap is sometimes mistaken for chanterelles because the color is similar. Remember that instead of gills, a chanterelle has thick, forking ridges; there's more on this in the article chanterelle lookalikes.

One more detail shows just why you can never be sure with webcaps. In 2016 American researchers found orellanine in the red banded webcap, which had previously been considered non-poisonous. The concentration was very low, less than one percent of that in the deadly webcap, but the finding itself matters: the toxins in this genus are far from fully studied.

Two shots we left in the forest

Here's a different kind of find, and exactly the kind of mushroom to be most careful with: a smooth brown cap and a long, fibrous stem with rusty lengthwise fibers. It was growing in grass, next to pine cones and fallen oak leaves, in early October 2026.

It may be a webcap, or it may belong to a completely different genus: there were no young mushrooms with a cortina nearby, and we didn't take a spore print. Most importantly, a dangerous lookalike can't be ruled out here. Medium size, a rusty-brown cap, a fibrous stem: this is the classic “ordinary brown mushroom” that could be hiding anything, including a webcap with orellanine. So our caption is an honest one: “unknown brown gilled mushroom, possibly a webcap”. We photographed it and moved on, and we advise you to do the same with any brown gilled mushroom you don't know for certain.

The gypsy mushroom: the edible exception among webcaps

Among the webcaps there's one mushroom that people in many countries are happy to gather: the gypsy mushroom (Cortinarius caperatus, Rozites caperata in older guides). It's edible, and you can recognize it by a combination of features:

• a cap 7–14 cm across, ochre-yellowish, wrinkled with age, looking as if dusted with fine silvery fibers;
• on the stem, a true white membranous ring, persistent, rather than the cobwebby threads of most webcaps;
• gills pale clay-colored at first, then brown; spore print rusty brown;
• grows mainly in coniferous forests, also with beech and among bilberry and heather; season August–October.

Even here, though, there are two caveats. First, if you've never picked the gypsy mushroom before, pick it the first time only with someone who knows it well. Second, and less well known: the gypsy mushroom is one of the forest mushrooms that accumulate radioactive cesium most strongly. In Poland, even decades after the Chernobyl accident, gypsy mushrooms often showed levels above EU limits. So in areas with contaminated soils, go by local radiological monitoring; according to the same research, boiling and pouring off the water reduces the amount of cesium that ends up in the dish.

If someone has already eaten a webcap

Don't wait for symptoms. With orellanine poisoning every day counts, and the quiet period can last a week or longer, so how you feel proves nothing here. See a doctor, say that you ate wild mushrooms and exactly when, and take any leftover mushrooms or photos of them with you. Blood and urine tests of kidney function will show whether there's a problem. What to do in the first hours is covered in our article mushroom poisoning: signs and first aid.

In short: you can recognize a webcap by its cortina and rusty spores, but you can't recognize the species. So for us, all webcaps except the familiar gypsy mushroom are mushrooms for the camera, not the frying pan.