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Mushroom, Toadstool, Bolete, Stinkhorn, or ?

by Timber Press on October 9, 2017

in Food, Natural History

So what do you call it?

From a botanical perspective, a mushroom is a fleshy fungus fruit body that has gills, or lamellae, that are covered with the reproductive layer, the hymenium. This hymenium produces basidia, which are the club-shaped cells that produce the sexual spores, the basidiospores. The term toadstool has often been used to designate a poisonous mushroom, but that is not a hard-and-fast rule.

The term mushroom also has been very loosely applied to the fleshy pore fungi, the boletes or bolete mushrooms. The hymenium covers the inside of each tube and the spores fall out of the opening, or pore, as gravity pulls the released spores down and out of the tubes. Calling boletes mushrooms seems okay, since the true mushrooms and boletes are closely related and you can only tell you have a bolete after you turn it over and see the tubes. However, for accurate and more precise communication, I suggest learning the distinctions between the various groups of fleshy macrofungi and using their common names.

The structures that produce the hymenium help, in an artificial way, to define these groups. For example, coral fungi have the hymenium covering the erect branches, while tooth fungi have the hymenium covering each tooth. These major groups are easily recognized, and when you tell someone you found a stinkhorn, they know exactly what you mean. If you say you found a smelly mushroom, that could just be a bolete that is rotting and smells bad.

All these groups are basidiomycetes except the cup fungi and stromatic fungi or pyrenomycetes, which are ascomycetes. Basidiomycetes produce sexual spores on top of club-shaped cells called basidia in the hymenium. Ascomycetes produce sexual spores in clusters of long tube- or saclike cells called asci (ascus is singular) in the hymenium that, for instance, lines the cup in a discomycete.

Learning these major groups also makes it easier and faster when trying to narrow down the choices for identifying a fungus to genus and species.

Mushroom Structures
Parts of mushrooms and other macrofungi structures are illustrated on the inside front and back covers of this book. These images will help you use the field guide more effectively. I have tried to keep scientific mycological terms to a minimum, but specific terminology is very important when discussing the minute features that help differentiate one fungus from another.

Although the form of a mushroom fruit body usually changes in shape over time, its features are consistent for each species. For instance, some species have conical-shaped caps while others have convex- shaped caps in the early form, but the caps of each species may both become plane, or flattened, with age.

The mushroom is at first protecting its reproductive surface, the gills, as it pushes its conical or convex cap up through the soil or other substrate. Once in the air currents, the cap fully expands, becomes plane, and the spores are released from the basidia, dropping down between the gills to the wafting air currents below the edges of the gills. The spores are then carried away to find new substrates in which to grow. When you make a spore print, you are catching these spores en masse to determine their color, since this feature is important for identification.

Gills bluntly attached (adnate).

Gills on mushrooms are generally thin and plate- or leaflike. They can be attached to the stem in various ways, or not attached to the stem, in which case they are referred to as free. In this guide, barely attached refers to gills that are adnexed, bluntly attached is adnate or emarginate, notched is sinuate, and decurrent is the standard term used for gills running down a stem. Noting attachment and spacing is very helpful when identifying mushrooms.

Gills are generally classified into two types: the lamellae are those that reach the stem, and the lamellulae are the shorter gills that may go halfway or just a short distance from the margin. If the gills are forked repeatedly and equally, dichotomously forked, this feature is characteristic for genera such as Cantharellula and Hygrophoropsis. When the edge of the gills is differently pigmented than the face of the gills, they are termed marginate. This is a diagnostic feature at the species level, for example in the case of Leptonia foliomarginata. If the gills peel away from the cap easily, that is also a diagnostic feature for genera like Tapinella and Paxillus.

Gills decurrent, stem hollow.

Mushrooms (but not all fleshy macrofungi) always have a cap and gills, but they may or may not have a stalk, or stem, technically called the stipe. Stalkless mushrooms are referred to as sessile and usually are attached to a substrate like wood, living or dead herbaceous plants, or another fungus (see Phyllotopsis nidulans). If the stalk is attached at the margin of the cap, it is called lateral; these are usually found on woody substrates (see Pleurotus pulmonarius). If the stalk is off -center, it is called eccentric, and the fruit bodies may or may not be on woody substrates (see Hygrophoropsis aurantiaca). These diff erent designs are just diff erent ways to get the gills up into the air currents.

Interestingly, both gills and stalks when present are often gravitropic. That is, they bend in response to gravity to orient the cap and gills to be perpendicular to the earth’s surface, so the spores can be precisely dropped from between the gills once they are shot off the basidia. Amanitas often show this gravitropic response. After they have been lying fl at in a basket or box for several hours, you will notice the stalk and cap have curved, reorienting to the pull of gravity.

The shape of the stem is important, with the typical shape being equal. But you need to be keenly aware of the other shapes, as they can be diagnostic when trying to make a determination (for example, the rooting stems, or pseudorhiza, of Phaeocollybia and Hymenopellis). Also, the surface features of stems can be useful diagnostically. For example, the porcini (Boletus edulis) always produces a white reticulum, while other look- alike species produce a brown- colored reticulum (for example, Tylopilus felleus).

A common feature of many mushroom and bolete stems is to be dotted with fi ne, variously colored granules. These fi ne granules are usually at the apex of the stem and white, but on some boletes, such as Xerocomellus chrysenteron, they are rhubarb-red and cover the entire stem. If the dots are large and brown or black, they are referred to as scabers and are diagnostic for the bolete genera Leccinum and Leccinellum. Most mushrooms have unadorned stems; they are glabrous.

Mushroom emerging from its universal veil.

Protecting the reproductive spores is so important that certain groups of fungi evolved structures, such as the veil, to cover and more eff ectively protect the hymenium from damage by environmental stresses such as dry conditions and fungus-eating insects.

Some fungi have a partial veil that covers just the gills and then leaves a ring, the annulus, on the stem or a fringed margin on the cap, in which case the cap is described as appendiculate. This partial veil is more eff ective than not having this covering; however, the ultimate in protection of the hymenium in the early stages of development would be the universal veil that covers the entire fruit body. Evidence of a universal veil can be found as freely removable wartlike patches on the cap and a sheathing volva at the base of the stem after the fruit body has expanded, tearing the universal veil open.

The partial veil usually leaves a ring of tissue, called the ring or the annulus, resembling a skirt around the upper stem, after the cap expands. If it is substantial and membranelike, it is referred to as membranous and can be hanging down, pendant, or sticking out and fl aring. If the stem looks as though it is sheathed in this ring tissue from the base of the stem to where the ring is formed, the veil is called peronate or sheathing.

If the ring is spiderweb-like with lots of space between the individual strands and the strands are not confi ned to a single plane, but crisscrossed from the cap margin to the stem apex, that is a special veil called a cortina and is a diagnostic feature of Cortinarius. When a cortina or any fragile veil collapses on the stem and is barely noticeable, it is referred to as a ring zone.

The universal veil covers the entire fruit body in the very early stages of development, the button stage. When the universal veil is broken as the mushroom extends upward, parts of the veil are left as the volva surrounding the base of the stem and as warts on the cap in many cases.

The type of volva can be diagnostic for species of Amanita. The deadly poisonousA. phalloides, the death cap, and A. bisporigera and A. virosa, the destroying angels, have well-developed cup- or saclike membranous volvas. The very commonly found A. fl avoconia has yellow conical warts on the cap as remnants of the universal veil, while the volva at the base of the stem is friable, meaning it is soft and easily destroyed and lost. The distinctive collarlike band or circumsessile volva is diagnostic for A. frostiana, a species often confused with A. fl avoconia. The signature of the large orange-yellow-capped A. muscaria var. guessowii is the concentrically ringed volva at the base of the stem.


Timothy J. Baroni is a Distinguished Professor of Biology in the State University at New York. He teaches at SUNY–College at Cortland and works on biodiversity research of macrofungi globally, but with emphasis on mushrooms and other fungi found in the Americas.


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