Webcap Mushrooms: A Complete Guide

Have you ever noticed a mushroom with the stipe or gills covered in what looks like a sticky cobweb? If so, you’re almost certainly looking at a species of webcap mushroom! These wonderfully strange fungi exist across the world and are a treat to stumble across. These species are notoriously difficult to distinguish. With some containing seriously poisonous toxins, this genus of mushrooms is best to admire only!

In this guide, we’ll cover the fungal classification of webcap mushrooms. We will also describe some of webcap’s most notable defining characteristics and explain the debate involving subgenera classification. Finally, we will describe in detail one of the more easily identifiable species and cover the severe toxin present in some species.

So, without further ado, let’s jump in!

Webcap Mushrooms: Fungal Classification

The mushrooms commonly referred to as webcaps belong to the Cortinarius genus. This genus, which is part of the Cortinariaceae family, contains over 2,250 species! Mycologists currently consider Cortinarius as the largest known genus of agaric mushrooms. An agaric mushroom is typified by having a stipe, cap, and gills.

Researchers currently debate the question of dividing this genus of mushrooms. Traditionally, Cortinarius has been divided into various subgenera such as Cortinarius, Telamonia, Myxacium, Phlegmacium, and Leprocybe. However, recent genetic analysis has proven that much of this subdividing based on macroscopic and microscopic morphology does not equate to subgenera having closer genetic relationships. These older proposed subgenera date back to the 1980s.

More recently, some mycologists involved in molecular research have proposed the following subgenera of Cortinarius based on genetic evidence: Callistei, Camphorati, Illumini, and Orellani. This proposal is still under hearty debate. Since there is no current widespread agreement on the subgenera classification of Cortinarius, in this guide, we’ll stick to describing these mushrooms on the genus and species level.

Common Characteristics of Webcap Mushrooms

So, there are generally three agreed-upon defining characteristics of mushrooms in the Cortinarius genus. These features are:

1. A web-like partial veil called the cortina covers the gills of immature webcaps. Sometimes, parts of the thin, fibrous tissue of this veil may collapse around the upper portion of the stipe. This can occur as the mushroom cap expands, forming a web-like ring. This unique partial veil is what gives this mushroom both its common name of “webcap” and the Latin name “Cortinarius.”
2. The spore print of webcap mushrooms is almost always rusty brown.
3. Webcap mushrooms are mycorrhizal in association with trees.

Other Features of Some Species

Other common characteristics of webcaps exist that don’t occur across all species but are used by some field guides to categorize the genus into the traditional subgenera. Typically, in attempting to categorize webcaps some guides will suggest noting the following:

1. Is the specimen’s cap, stipe, or both slimy? Some species have a slimy cap with a dry stipe, while others have both a slimy cap and stipe.
2. Does the cap of the specimen notably fade in color as it dries? We call this a hygrophanous cap.
3. Is the stem regular in size from top to base, or does the base swell or appear club-shaped?
4. Does the stem contain a partial veil ring or remnants of the cob web-like partial veil?
5. What does the specimen smell like? Reported odors of various species range from radish-like to sweet, mild, and rancid.

It’s important to note that many field guides only describe a handful of species that you can reasonably identify based on macroscopic (what you can see with the naked eye) morphology. Like russulas, most of the species of Cortinarius are effectively indistinguishable from each other or can only be categorized down to group species or loose subgenera based on morphology. To truly identify most mushrooms in this genus, genetic analysis or intensive microscopic observation of many specimens is often required.

As such, we’ll describe in detail below two of the most commonly cited, identifiable North American webcap species.

Violet Webcap

So, many webcaps contain varying degrees of toxicity to humans (more on this later). However, the violet webcap (Cortinarius violaceus) is one of the few webcaps widely considered edible. It’s probably still a best practice, though, to refrain from consuming webcaps due to the overall difficulty in identifying this genus. Additionally, as we’ll discuss below, one of the main identifying features of this mushroom fades with age, so unless you find young specimens, confirming this species with macroscopic observation won’t be reliable.

The Cap

When young, the cap is a brilliant violet color and covered in dense hairs that can become scaly as the mushroom matures. Initially, the cap is convex and becomes more broadly convex or flattened with age. Typically, this species can reach up to 5 inches across. As the mushroom matures, the brilliant violet color fades to brownish purple or dark brown.

The Gills

Like the cap, the gills of a young violet webcap specimen are a stunning purple. The gills of the immature mushroom is covered in the thin strands of a purple cortina (web-like partial veil). As the specimen matures, the gills eventually turn dark brown, as reflected by the mature, rusty brown spores. The almost wavy gills are not crowded and are attached to the stipe.

The Stipe

The stipe of a young violet webcap is vividly purple and covered in fine hairs. Like the other parts of this mushroom, the color fades with age, although it tends to take on more of a purplish gray shade than brown. It typically reaches up to 6 inches tall and about 3/4 of an inch thick. As it matures, the stipe becomes hollow. The base of Cortinarius violaceus is generally either swollen or club-shaped.

Ecology

Like all webcap mushrooms, this species is mycorrhizal with trees, meaning it derives its nutrients from a symbiotic plant-fungi nutrient exchange. Cortinarius violaceus is widely distributed across North America, and you can find it growing mycorrhizal with both hardwoods and conifers. On the West Coast, it appears to have an affinity for growing in towering old-growth conifer forests, such as the stunning old-growth redwood forests. Imagine the beauty of walking through the forests of the redwood giants and finding these stunning purple mushrooms along your path!

Toxicity of Webcap Mushrooms

This genus of mushrooms contains many toxic-to-humans species, including ones with common names such as lethal/deadly webcap (Cortinarius rubellus). Deadly webcap, among some other species which are sometimes described as belonging to the Orellani subgenera, contains the nephrotoxin, orellanine. As a nephrotoxin, orellanine damages the kidney and can lead to acute kidney failure and long-term kidney insufficiency. Kidney damage signs and symptoms typically appear 1-2 weeks after ingesting a webcap mushroom containing orellanine. Some poisoning victims may experience gastrointestinal upset in the days or weeks prior to signs of kidney damage. Currently, no antidote for orellanine poisoning is known, and treatment typically involves preventing further harm to the kidneys and management of long-term kidney insufficiency if it occurs.

In one almost 20-year study completed on 28 patients who suffered acute kidney injury from accidental ingestion of deadly webcap (Cortinarius rubellus), 75% of patients developed stage 5 chronic kidney disease and over 70% eventually required transplantation.

Given these outcomes and the difficulty in distinguishing species, most guides, in addition to this one, do not recommend foraging for edible webcap mushrooms. But remember, fungi play an incredibly important role in our ecosystem, and while some of these species are toxic to humans, they contribute immensely to the health of our environment. In the case of webcaps, they improve the health of the soil and provide powerful nutrient boosts to various species of trees in hardwood and conifer forests around the world!

The photo featured at the top of this post is © Phant/Shutterstock.com

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