Fungi are organisms full of superlatives. Ranging from tiny to enormous, they inhabit the entire Earth, either alone or in communities. We find them in forests, in the soil, as spores in the air, in and on living organisms, and as pests. Some are edible, many are inedible, and a few are deadly. Hardly any other life form is as diverse as fungi.

They are classified as neither animals nor plants. This is because fungi are not capable of photosynthesis like plants and therefore feed heterotrophically, like animals. That is, they absorb their nutrients from the environment. Fungi are often mistaken for plants because they are “sedentary,” yet genetically they are actually more closely related to animals. They differ from animals, for example, in that they can form cell walls—a characteristic usually associated with plants.

Most edible mushrooms belong to the Basidiomycota. The only part visible to us on the surface is their fruiting body, which is formed for reproduction via spores. The spores are dispersed into the environment by wind, rain, or animals. The largest part of the organism, the mycelium, lies deep underground in a branched network. Through the mycelium, mushrooms absorb nutrients, use them themselves, or pass them on to symbiotic partners. The individual branches of the mycelium (hyphae) can spread over several kilometers and always seek out areas with high nutrient concentrations in the surrounding environment. Incidentally, the mycelium of some species of honey mushrooms extends over nearly 9 km².

Forests would be unthinkable without the network that fungi form with their mycelium. In their role as decomposers, they break down dead organic material and then return it to the cycle of life in the form of nutrients. Researchers now believe that trees can even communicate with one another through this network. That is why this network is also called the “Wood Wide Web.”

Mycorrhiza refers to a form of symbiosis between fungi and plants in which a fungus is in contact with a plant’s fine root system. Mycorrhizal fungi supply the plant with salts such as phosphate and nitrate, as well as water, and in return receive a portion of the sugar produced by the photosynthesis of (green) plants. Mycorrhizal fungi also protect trees from pollutants and secrete antibiotic substances against root-pathogenic soil organisms. Mycorrhizal fungi also play a crucial role in the global carbon cycle through their ability to sequester large amounts of carbon dioxide (CO2).

Wood-decaying fungi in nature are important contributors to the ecosystem. They break down dead wood, decompose cellulose and lignin, form humus, and return important nutrients such as carbon dioxide and minerals to the natural cycle. They are one of the most important elements in the age-related decay of forests, as they ultimately completely decompose even the hardest dead oak wood. In doing so, they fulfill the vital role of “cleaning up” the forest ecosystem and supplying the soil with organic matter.

In urban areas, such as parks, fungi that invade weakened trees through wounds or via the roots can cause major problems with stability or the risk of breakage. Some of these fungi, such as the lacquer polypore, form long-lived, perennial fruiting bodies that are easily recognizable on the tree. Others, on the other hand, form only annual fruiting bodies, such as the sulfur polypore, which decompose over the course of the year, making it difficult to detect an infestation. Some of these tree fungi, such as the sulfur polypore, the oyster mushroom, or the rattling sponge, are edible.

In Mainz’s parks and cemeteries, trunks or parts of dead trees—so-called biotope or habitat trees—may be left in place. In addition to providing a habitat for fungi, they serve as an important habitat, food source, and breeding ground for animals and plants.

The German Society for Mycology (DGfM) states that of the estimated 14,400 mushroom species in Germany, only about 200 are edible and 150 are poisonous. Of these, 10 species are classified as deadly poisonous mushrooms. The remaining mushroom species are considered inedible—that is, they do not taste good, are indigestible, are too small or too hard, or their toxic effects have not yet been studied. The DGfM offers the following tips for collecting edible mushrooms:

In general, collecting the above-ground fruiting bodies does not harm the fungal mycelium in the soil. It does not matter whether the mushrooms are cut off or twisted out of the ground. However, it is recommended to remove mushrooms from the ground carefully, as important identification characteristics are often found at the base of the stem. 

Collect only mushroom species that you are certain you can identify. For unknown mushrooms, you can take 2–3 specimens at different stages of development—if possible—and identify them at home at your leisure. Store unknown mushrooms separately from edible mushrooms, as even small pieces of a deadly poisonous mushroom can spoil the entire basket.

Collect only healthy, fresh mushrooms and leave overmature and oversized specimens where they are. They are a valuable source of spores for the next generation. Very small mushrooms often haven’t yet developed their identifying characteristics—leave them alone to grow for the next collector.

Nature conservation rules also apply to mushrooms: Many edible mushrooms, such as porcini, red-capped mushrooms, and chanterelles, are protected by law and may only be collected in small quantities for personal use. A general guideline is about 1–2 kg per collector per day. Some species are fully protected and may not be collected at all.

Collect the mushrooms in a basket so they can be well-ventilated. Plastic bags are completely unsuitable, as the mushrooms “sweat” inside them and decompose very easily.

If you consult a mushroom expert for help with identification, please present all your finds. This is because only mushrooms that are physically presented can be approved for consumption.

The most important habitat for native edible mushrooms is the forest, especially old mixed forests with deciduous and coniferous trees. Mushrooms grow there in the soil or on wood. There is very little forest in Mainz overall. Mushroom picking is prohibited in the Lenneberg Forest and the Ober-Olmer Forest, as these are nature reserves. To go mushroom hunting, you’ll need to head to surrounding regions such as the Binger Forest, the Soonwald, or the Hunsrück.

In September and October, we provided you with information on the topics of mushrooms and habitat trees: events and contacts in and around Mainz, a “do-it-yourself” guide to creating a mushroom garden, and much more. On Friday, October 9, 2026, from 4:30 p.m. to approximately 6:00 p.m., the Parks and Environment Department will host an excursion titled “Habitat Trees in the Drususwall—A Habitat for Plants and Animals.” Registration is available at the Mainz Environmental Store.