This Amanita mushroom, found next to the Norwottuck Rail Trail in Amherst, is most likely a fly agaric (Amanita muscaria), a species that is found across much of the northern hemisphere. A. muscaria is usually associated with birch or pine trees and is poisonous but not usually fatal. It has bright red forms and white ones, as well as the yellow version shown here. PHOTO BY JOSHUA ROSE

Fungi — bane or blessing? Nuisance or nourishing? Delicious or deadly? Answer: Yes, and more.

On the plus side, as I explain below, many of Earth’s plant and animal species depend on fungi. On the minus side, fungi have been implicated in widespread declines, disappearances and even extinctions of a number of animal and plant species. And eating them could be either a big plus or huge minus.

When we hear the word “fungus,” most of us think of a mushroom, but this is incomplete in two ways. First, fungi have a far greater diversity than just the mushroom-producing species. The mold that turns bread fuzzy and puts the blue in blue cheese? Fungi.

Ringworm? Not a worm at all, but a fungus. The active ingredients (literally) of bread, beer and soy sauce? Fungi. The diseases that caused the declines, disappearances or extinctions of the American elm, American chestnut and dozens of species of frogs, toads and salamanders? Fungi. Truffles, the subterranean lumps prized for cooking? Fungi.

Second, as David Spector wrote in a previous Earth Matters column (“The Giant Elves of Fall,” October 2014), a mushroom is not a complete organism. The majority of the organism’s mass is a vast network of fibers through the soil, sending the occasional mushroom up through the surface. A mushroom is the fungus’s mechanism for spreading its offspring, spores that can travel to suitable habitat and germinate into new fungi. A mushroom is like a fruit, but the “tree” grows underground and is all roots with no trunk, branches or leaves.

Mushrooms use a variety of techniques to disperse their offspring. The most common is having the underside of the mushroom’s cap covered with gills, pores or other structures which drop spores into the air below to be spread around by the wind. The ever-popular puffballs reverse this direction, poofing their spores upward instead of dropping them downward. The tiny bird’s-nest fungus grows a cup-like shape, the “nest,” adapted to redirect raindrops into splashing its “eggs” (actually packets of spores) away to new homes.

Truffles, unable to disperse by wind or water because they grow entirely under the soil, evolved their uniquely appealing odor and flavor to entice animals (most famously pigs) to dig them up and eat them, later spreading the truffles’ spores in their feces. And then there are the stinkhorns, which combine a distinctive shape — their genus name Phallus provides a hint — with a horrible smell that attracts flies which leave with spores stuck to their feet, carrying them toward manure or compost with odors not so different from the stinkhorn’s own.

Fungi have many different relationships with other organisms. Many plants are unable to survive without mycorrhizal fungi: most orchid seeds must connect to the right species of fungus to germinate, and the ghost pipes flowering in our local forests survive without chlorophyll thanks to mycorrhizae bringing them nutrients from decomposing plant matter. Lichens can colonize some of the most barren habitats on Earth by combining the toughness and dispersal ability of fungi with the photosynthetic powers of algae.

Some insect-fungus partnerships flip this equation, with the insects providing the transportation, and the fungi the food. Ambrosia beetles and some gall midges have evolved mycangia, crevices in their exoskeleton adapted to carry fungus propagules; the insects fly from plant to plant, laying eggs and depositing fungi.

The fungi compensate the beetles by partially digesting wood, allowing the beetles’ larvae to eat it. Dutch Elm Disease is the most infamous example, enabled when we accidentally introduced a European ambrosia beetle species to the U.S. For the midges, the fungi induce the plant to develop galls that provide the larvae with shelter and food. Leafcutter ants grow a fungus, essential to their nutrition, atop mounds of leaf-cuttings; new queens carry a little chunk of it in their mouthparts when they leave to found a new colony.

Fungi are less kind to other arthropods. Along Amethyst Brook, on the undersides of leaves, I sometimes find small, pale, dome-shaped structures covered with fingerlike projections. Some of these upside-down lumps show hints of the spider they used to be. A fungus infected these spiders and consumed them, then grew the projections to disperse spores that will infect other spiders. Other fungi do the same to insects; one of these, Cordyceps, has become a popular health supplement, humans eating fungus-digested insects.

If we eat mushrooms, the consequences vary wildly from species to species. A single genus, Amanita, covers the entire spectrum. Massachusetts is home to dozens of Amanita species. Some, like the tawny grisette, the blusher, and Jackson’s slender Caesar, are edible. Then there’s the death cap, the destroying angel, and the poison champagne Amanita, whose names communicate the consequences of eating them. The edibility of many other Amanita species remains unknown to this day. As members of the same genus, these species can be very difficult to tell apart, which might explain why 90% of the human fatalities from mushroom poisoning are linked to Amanitas.

In other words, don’t try this at home.

Joshua Rose is a naturalist who lives in Amherst. He is vice president of the Hampshire Bird Club, Northeast Chapter head of the Dragonfly Society of the Americas and a contributing editor of the website bugguide.net; he regularly leads programs for local nature-oriented groups.

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