Decomposing Fungi

A patch of small white mushrooms growing on a rotting log.
Pleurocybella porrigens, a species that causes white rot in conifers.

NPS Photo

Mushrooms that get their nutrients by digesting dead or decaying organic matter such as leaves, pine needles, and wood are known as saprobes. Saprobic fungi play a major role in breaking down and recycling wood and other forest debris, creating healthy soil, and freeing up nutrients for microbes, insects, and growing plants.

When you visit Mount Rainier’s lowland forests, take a moment to notice the signs of decomposition going on all around you. Towering, bark-less Douglas-fir snags, fallen nurse logs cradling new life, browning leaves and needles beneath your feet—all these things are in the process of being consumed and recycled by various types of fungi. Even when mushrooms are not present, you can observe these vital processes in action. The following are two very common forms of wood decomposition often caused by fungi.

 
A rotting log breaking up into chunks.
Brown rot on coniferous wood.

NPS/B. Garcia Photo

Brown Rot
Dark, hard, brittle wood that fractures and breaks up into cube-like chunks. This type of decomposition is the result of mycelial networks that digest cellulose, while leaving the wood’s lignin intact. Many different species of fungi cause brown rot, which occurs most often in the wood of coniferous trees.

 
Rotting wood breaking down into pale fibers.
White rot on deciduous wood.

NPS/B. Garcia Photo

White Rot
Soft, spongy, moist, stringy, and lighter in color than brown rot. White rots occur when wood is colonized by a fungus that digests lignin and sometimes cellulose as well. They are most prevalent on hardwood trees but can occasionally affect conifers as well.

 

In addition to their importance in terms of nutrient cycling and decomposition, a number of saprobic fungi are esteemed edibles. Oyster mushrooms, chicken of the woods, Hericium spp., and others draw mushroom hunters into the woods each fall. Indeed, even the common grocery store mushroom, Agaricus bisporus (often marketed as “White Button,” “Cremini,” or “Portobello”) is a decomposer.

Some saprobic fungi have even demonstrated an ability to digest toxic and traditionally non-biodegradable materials such as pesticides, heavy metals, and petroleum products. Mycelium of the oyster mushroom (Pleurotus ostreatus), in some settings, has been able to drastically reduce harmful contaminants associated with oil spills in samples of sand and soil. The use of fungi to break down or reduce pollutants in the environment, or mycoremediation, is a burgeoning field, which may eventually offer affordable solutions to issues involving toxic waste and environmental contamination.

 
Three ear-shaped white mushrooms growing out of moss.
Pleurotus pulmonarius, the oyster mushroom.

NPS/B. Garcia Photo

Pleurotus Pulmonarius

Common Name: Oyster mushroom
Description: Growing in shelves and clusters on dead or living trees. Ear or seashell shaped. White to cream flesh with white gills running down a rudimentary stalk. Spores white. Often fruiting in wet, cool weather in the spring and fall.
Ecology: Saprobic, causing white rot in hardwoods. This mushroom is also carnivorous! It has evolved the ability to ensnare and digest microscopic nematodes on its cap surface.
Notes: Pleurotus species are important in the field of mycoremediation, as they have demonstrated the potential to digest harmful environmental contaminants including certain types of plastics and other petroleum products.

 
A two-layered brown mushroom growing out of a tree trunk.
Fomitopsis mounceae exuding metabolic droplets in a process known as guttation.

NPS/B. Garcia Photo

Fomitopsis mounceae

Common Name: Northern red-belted conk
Description: Tough and woody, white to cream pore surface (underside) with a brownish top. Most specimens display a conspicuous reddish band on the outer edge of the cap, with a whitish border. This mushroom is perennial and persistent, forming a new pore surface each year. Try counting the lines on the upper surface to estimate the age of the mushroom!
Ecology: Saprobic, causing brown rot in conifers and occasionally hardwoods. Sometimes parasitic on living trees.

 
A patch of pink-red mushrooms growing out of a rotting log.
Mycena haematopus, the Bleeding Mycena, causing white rot on the log it has colonized.

NPS/B. Garcia Photo

Mycena haematopus group

Common Name: Bleeding Mycena
Description: Small to medium delicate mushrooms. Cap, stem and gills pinkish, reddish, or brownish. Growing in groups on wood. When squeezed, the stem exudes a dark-red fluid resembling blood.
Ecology: Saprobic, likely causing white rot on hardwoods.

 
A string of small yellowish mushrooms growing along a log.
Hypholoma fasciculare, the sulphur tuft, a poisonous decomposer.

NPS/B. Garcia Photo

Hypholoma fasciculare

Common Name: Sulphur tuft
Description: Small to medium, bright yellow, yellow-orange, or greenish-yellow mushrooms growing on wood. Gills yellow, becoming greenish-yellow at maturity. Often growing in large, dense clusters, on coniferous wood in the fall. Spores purple-brown.
Ecology: Saprobic on decaying hardwood and conifers.
Notes: This common mushroom is probably toxic, reportedly causing severe gastrointestinal distress! The gills glow brightly under UV light. This mushroom has been strategically introduced into recently logged areas in order to supplant the much more desctructive Armillaria ostoyae, or honey fungus.

 
A brown and white striped conk mushroom growing out of a log.
Laricifomes officinalis, the agarikon, growing from the base of a fallen conifer.

NPS/B. Garcia Photo

Laricifomes officinalis

Common Name: Agarikon, quinine fungus
Description: Medium to large, hard, perennial fruit body. Cylindrical, sometimes shaped like a hoof. Distinct layers stacked vertically, with white (actively growing) pore surface at base. Most specimens have a bright, medicinal, lemony scent.
Ecology: Saprobic/parasitic, causing excessive rot in the heartwood of old-growth conifers.
Notes: This fungus can cause such excessive rot that a single conk on a tree is enough to make a tree “highly likely to fail” (or make the tree hazardous if its near something it can hit). However, the agarikon is well known for its purported medicinal value. In the past, it has been used as a substitute for quinine (an ingredient in tonic water) due to its bitter, medicinal taste. Fruit bodies are fairly uncommon and can persist for many decades, so it is good practice to refrain from harvesting this species. If you count the bands, you can estimate the age of the mushroom, as each layer marks a growing season!

 
A string of bright yellow gumdrop-like mushrooms along a log.
Guepiniopsis alpina often grows in bright, cheery clusters in the spring.

NPS/B. Garcia Photo

Guepiniopsis alpina

Common Name: Poor man’s gumdrop
Description: Small, yellow, bell-shaped fruiting bodies. Gelatinous, usually with ridges on outer edges. Often growing in large groups on decaying wood.
Ecology: Saprobic on coniferous wood
Notes: This is a very common springtime (April-June) mushroom at Mount Rainier. Look for it on the Rampart Ridge trail near Longmire!

 
 

Last updated: April 21, 2021

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