Fungus

fungus [ FUHNG-guhs ] noun, plural funguses or fungi [ FUHN-jahy, FUHNG-gahy ]: a kingdom of saprophytic or parasitic spore-producing, typically filamentous, organisms that lack chlorophyll 

hypha [ HAHY-fuh ] noun, plural hyphae [ HAHY-fee ]: one of the long, branching multi-cellular threads that make up the mycelium of a fungus, and grows from the apex; adjective hyphal [ HAHY-fuhl ]

mildew [ MIL-doo, -dyoo ] noun: a type of fungus that typically appears as a thin, whitish coating on the surface of impacted parts 

mold [ mohld ] noun: microscopic fungi growing as filaments (hyphae) 

mushroom [ MUHSH-room, -room ] noun: an aboveground, fleshy fruiting body of a fungus usually consisting of a stalk and umbrella-shaped cap

mycelium [ mahy-SEE-lee-uhm ] noun, plural mycelia [ mahy-SEE-lee-uh ]: a network of interwoven filamentous hyphae that forms the main vegetative body of a fungus 

mycorrhiza [ mahy-kuh–RAHY-zuh ] noun, plural mycorrhizae [ mahy-kuh–RAHY-zee ]: the symbiotic association of the mycelium of a fungus with the roots of a seed plant that acts to extend the reach of the plant’s root system; adjective mycorrhizal [ mahy-kuh–RAHY-zuhl ]

rust [ ruhst ] noun: a fungus in the order Pucciniales, which produces reddish-brown, orange, or yellow spores that infect a variety of plants

smut [ smuht ] noun: a fungus in the order Ustilaginales, which produces dark, powdery spores that infect plants, mostly in the grass family

yeast [ yeest ] noun:  a unicellular fungus, usually having little or no mycelium, capable of active reproduction by budding or, occasionally by fission 

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Formerly classified as plants, fungi are neither plants nor animals but a separate kingdom of their own. Fungi are eukaryotic organisms, meaning they have cells with membrane-bound nuclei. They are also heterotrophic, meaning they absorb nutrients from their environment instead of producing their own food like plants do. They include rusts, smuts, mildews, molds, mushrooms, and yeasts. 

Often associated with dark and damp places, fungi can be a bane in the garden, causing disease and death. Rusts produce reddish-orange spores, while smuts have blackish spores, both of which can damage plants and reduce crop yields. Powdery mildew, a common mold that grows typically on the surfaces of plant leaves and stems, can hinder photosynthesis and stunt growth. Deeper-penetrating molds can negatively affect root systems, leading to poor nutrient absorption and root rot. Both mildew and mold pose risks to human health, including allergies, asthma, and respiratory problems. Pathogenic mushrooms can decompose woody tissue, leading to plant decline or death. Some contain toxic compounds that can be harmful or fatal if ingested. Certain yeasts can contribute to plant diseases or spoilage in fruits and vegetables.

However, fungi also can have useful functions. Certain molds play a vital role in pharmaceuticals and food production—Penicillium species are not only used in antibiotics but are responsible for the distinctive flavors of cheeses like brie, gorgonzola, and Roquefort. Edible mushrooms serve as nutritious, low-calorie food sources. Yeasts are essential in food production, such as in making bread, beer, and wine. Furthermore, they can enhance soil health, benefiting overall plant growth. 

Some fungi form symbiotic relationships. A lichen is a symbiotic union of a fungus and an alga. Mycorrhiza is the symbiotic association of the mycelium of a fungus with the roots of a seed plant. The role of fungus in expanding the reach of plants’ root systems through mycorrhizae and how they improve access to the soil and its nutrients as well as information from surrounding plants has been explored and scientifically explained in more recent decades.

Understanding that expanded root area and its function helps explain why weeds are the first things that often grow in soil that was formerly disturbed by urban development or other destructive uses. Without living plants to partner with, fungi would not grow there either, resulting in a soil lacking many nutrients and even easy access to retained water. Weeds that make lower demands on that poor soil are more likely to thrive than cultivated plants inserted by a hopeful gardener. However, once they spend time there, living and dying, attracting insects and other creatures, and gradually adding nutrients, then the mycorrhizal environment starts to improve and the networks begin to grow. 

The type of mycorrhizae that typically grows in partnership with the roots of trees, such as pine and oak, is ectomycorrhizal fungi. In ectomycorrhizae, the fungal hyphae form a protective mantle around the plant roots without penetrating the root cells. Truffles, a highly prized delicacy in various cuisines, are ectomycorrhizal fungi. In contrast, endomycorrhizae involve fungal hyphae that penetrate the root cells and are commonly associated with the roots of herbaceous plants, including many perennials, grasses, and agricultural crops such as maize, wheat, and soybeans. This partnership allows plants better access to essential nutrients and water in exchange for providing fungi with carbohydrates produced through photosynthesis.

Gardeners can encourage the growth of mycorrhiza by “leaving the leaves” in their garden beds and around their trees and shrubs in fall. Doug Tallamy says that “leaf litter is the perfect protection for our soil community, which then encourages our plants, our root growth and mycorrhizal interactions.”

Note: Click on images to see enlarged photos.

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References

Brown, JR. September/October 2025. “The Fungal Frontier.”  American Gardener. The American Horticultural Society, 7931 East Boulevard Drive, Alexandria, VA  22308.

Roach M. 2020. fall cleanup with ecology in mind, with doug tallamy. A Way to the Garden.

Sheldrake M. 2020. Entangled Life: How Fungi Make Our Worlds, Change Our Minds & Shape Our Futures. Random House. Penguin Random House LLC, New York. ISBN: 978-0-525-51031-4.

Simard S. 2021. Finding the Mother Tree: Discovering the Wisdom of the Forest. Alfred A. Knopf. Penguin Random House LLC, New York. ISBN: 97805250525656098.