This Is a Book for People Who Love Mushrooms

What Is a Mushroom?

Ask just about anyone to draw a mushroom, and they’ll likely sketch the classic toadstool: a tan- or red-domed cap—maybe with spots—a stem, and possibly some gills. These are the images of mushrooms many Americans are exposed to the most, whether through literature and popular culture or because these are the most common types found in US supermarkets and cuisine.

But in reality, mushrooms come in myriad shapes, textures, and sizes, as well as every color of the rainbow. Some are tiny bowls, cups, or spoons fit for faerie feasts. There are species that look like daisy-petaled flowers, discarded citrus peels, miniature birds’ nests complete with eggs, and even wrinkled brains and spooky zombie fingers poking from the earth. Many have the appearance of ocean life—seashells, starfish, anemones, spiny urchins, squid tentacles, and fantastical branched corals—organisms that look like they would be more at home under the sea than growing from the forest floor. Some are so small they can hardly be seen with the naked eye, while some are so large they could barely fit in a wheelbarrow.

But what is a mushroom, exactly? Mushrooms are fruiting bodies; much like an apple is the reproductive structure of a tree, a mushroom is the visible reproductive structure of a fungus. Most of a fungus’s mass exists largely out of view in the soil, under leaves and logs, and embedded in the substrate it is growing in. This hidden portion is made up of an extensive net of thread-like tissue called mycelium. Mycelium secretes enzymes for digestion and absorbs water and nutrients for the fungus. It also can connect plants and trees in a mutualistic network much like Mother Nature’s internet. In a thriving environment, under ideal conditions, there can be an astounding seven to eight miles of mycelium in one cubic inch of soil.

One of the primary goals of living organisms is to reproduce and ensure the survival of their species. When it is time for fungi to do so, they form mushrooms, which in turn produce spores containing the fungal organism’s genetic material. This process uses up a tremendous amount of energy and resources, so it must be timed wisely to take advantage of the moist conditions that most mushrooms require to reach reproductive maturity. This is why mushrooms are often found popping up in damp, shady forests and soggy lawns after a rainfall.

Anatomy of a Mushroom

Not all mushrooms are shaped like the classic toadstool, but those that are have many of the same basic parts. For everyone from casual nature enthusiasts interested in mycology as a hobby to serious foragers, learning about these structures is key to becoming proficient at identifying wild mushrooms. Some edible mushrooms have toxic look-alikes, so careful observation and knowledge of each species’ unique characteristics are especially important when foraging.

From our human perspective, the top of the mushroom is often the first part we observe, so it offers the first clues about a mushroom’s identity. The cap is called a pileus in mycological terms. Think of a grilled portobello and you’ll have a sense of exactly which part of the mushroom this is. A mushroom’s cap serves as protection, structure, and support for the fertile surface found on the underside. Caps come in every color imaginable, from dull and subdued to shockingly bright. They can be smaller than the head of a pin or as large as an open umbrella, pointy like a witch’s hat or concave like a dish. Their sheen ranges from dull and chalky to glossy as a sports car, and their endlessly diverse textures run the gamut from dry and leathery to gooey, slimy, warty, spiky, and even furry.

The more distinctive-looking mushrooms can be easily recognized solely by the features of their caps, but it is often necessary to study other parts of the mushroom as well. The underside of the cap is the next place to look. Called the hymenium, this is the fertile surface where spores are produced. Most people are familiar with gills, or lamellae, the ridges that radiate out from the stem like spokes on a wheel. The gills’ color, spacing, and means of attachment to the stem can all be key to a mushroom’s identity. The folds and ridges of the gills function to increase the surface area of the spore-producing hymenium. Other mushroom species have developed different means of maximizing this real estate. Some have evolved toothy projections, while others have developed long, spore-producing tubes that end in openings called pores.

A fungus’s goal is not only to produce as many spores as possible but also to ensure they have the best chance of traveling the farthest. A mushroom’s stem, or stipe, facilitates spore dispersal by elevating the fertile surface to an optimal height so spores can be distributed far and wide on air currents or carried by dining insects, hungry slugs and snails, passing animals, and even humans. Offering more clues about a mushroom’s identity, stems can be as diverse looking as other mushroom parts. Like caps, they come in every color and texture imaginable. In stature, they can be long and slender like a hair or stout and stocky enough to dwarf the cap, giving them the appearance of a person wearing a tiny hat many sizes too small for their head.

Certain mushrooms have specialized structures that can further aid in their identification. One example is the universal veil, an egg-like structure found at or under the soil line that encases and protects the young mushroom when it is first developing. In species of Amanita, a portion of the universal veil remains at the base of the mushroom’s stem as a bulb or cup-like sac called a volva. Immature stinkhorns are also enclosed in a universal veil. Some mushrooms have a partial veil—a thin, tissuey, cobwebby, or slimy membranous covering that protects the mushroom’s developing gills. After the cap fully expands, this partial veil tissue is often left behind as a ring or pendant skirt-like structure on the stem and sometimes as raised warts or patches on the mushroom’s cap.

Mushroom Classification and Names

Scientists categorize all living things into groups of similar organisms as a means of organization and to facilitate common communication about life on earth. Until the mid-nineteenth century there were two kingdoms of classification: animals and plants, and fungi were included with the latter. The rationale was that plants are rooted in place and produce their own food by means of photosynthesis. Animals, on the contrary, are free to move about but cannot make their own food. In the 1960s, as the life cycle of fungi became better understood—generally, that they can neither move nor make their own food—fungi finally got a kingdom of their own. Incidentally, fungi share a more recent common ancestor with animals than they do plants. That means that a morel is more closely related to you than to a daisy.

Fungi are further organized within this system into increasingly smaller groups based on shared characteristics. Their common names, the ones with which we are most familiar, are often whimsical—elf cups, fairy fingers, earthstars—or describe their appearance—hedgehog, coral, peanut butter cups. As descriptive as they are, these colloquial names can vary from region to region and country to country, leading to potential confusion. This is why the scientists who study fungi, known as mycologists, give each one an official genus and species name—usually with roots in Latin and Greek—so that everyone in the world, no matter their language, can accurately recognize them.

In reference materials, fungi are often listed by a common name first, followed by the genus and species names in italics. Until modern genetics, fungi were filed into these classifications based on their morphology, or physical appearance. The development of DNA sequencing has since turned this system on its head, and there has been a mass renaming of species and shuffling of fungi from one group to another ever since. Because mycologists are continually in the process of untangling fungal DNA, outdated genus and species names are common in older field guides and even on the internet.

Ecological Roles of Fungi

Fungi are everywhere—in our lawns and forests, in and on our bodies, and even lurking in that forgotten Tupperware container in the back of the fridge. While some fungi are harmful, the vast majority are beneficial to their environments and serve important ecological roles.

Some fungi act as parasites, infecting their hosts and sickening or even killing them. Common human ailments such as ringworm and athlete’s foot are caused by fungi. Pathogenic fungi like rusts and mildews regularly cause costly damage to important agricultural crops. Chestnut blight, Cryphonectria parasitica, was inadvertently introduced to North America from Southeast Asia at the turn of the twentieth century and in a few short decades wiped out billions of chestnut trees in the United States, nearly causing their extinction. Fungi even attack other fungi. Hypomyces lactifluorum parasitizes species of Lactarius and Russula, transforming them into the choice edible known as the lobster mushroom. Hands down, though, the fungal parasites that infect insects have to be among the most bizarre. These fungi keep their insect hosts alive but take complete control of their actions, using them as zombie minions to spread their spores for them.

A second group of fungi are the decomposers known as saprobes. Humans have a primal aversion to rotting things, developed to help us avoid eating spoiled food that could cause illness. But decay is an essential part of an ecosystem’s natural cycle and decomposers are nature’s recycling crew. They feed on dead organic matter, breaking it down into nutrients that can then be used by other organisms, and life begins anew. As the only multicellular organisms capable of breaking down lignin, the toughest parts of wood and leaves, fungi act as nature’s cleanup crew. Without them, every tree that has ever died would still be lying about in huge piles like enormous pick-up sticks, and the earth would be buried under an epic leaf pile.

The third group of fungi enter into mutualistic relationships, called mycorrhiza, with plants, including food crops and the trees in our forests. In fact, about 90 percent of land plants rely on partnerships with mycorrhizal fungi. Underground microscopic fungal filaments, called hyphae