Mushrooms can definitively grow on trees, indicating a complex biological interaction. Fungi belong to their own kingdom; they lack chlorophyll and cannot produce food through photosynthesis. This nutritional limitation means they must acquire energy by breaking down organic matter, making them nature’s primary recyclers. When a fungus encounters a tree, it establishes a relationship that can be neutral, destructive, or mutually beneficial to the host.
The Different Biological Roles of Tree Fungi
The interaction between a tree and a fungus falls into three distinct ecological roles, each impacting the tree’s health.
Saprobic fungi, or decomposers, feed only on dead organic material, such as fallen branches or dead heartwood. These fungi are beneficial to the ecosystem, as they break down tough polymers like lignin and cellulose, recycling essential nutrients back into the soil.
A second type is the parasitic fungus, which actively infects and consumes the tree’s living tissues, often causing disease or death. Parasites penetrate the tree’s cells to draw out nutrients, weakening the host and making it susceptible to stresses like wind damage. The presence of fungal fruiting bodies often signals serious decay within the tree’s structural wood.
The third relationship is the mycorrhizal association, a mutualistic partnership primarily with the tree’s root system. The fungus extends its vast network of filaments into the soil, drastically increasing the root’s ability to absorb water and vital minerals like phosphorus and nitrogen. In exchange, the tree provides the fungus with carbohydrates produced through photosynthesis.
Understanding Fungal Structure and Growth Location
The mushroom visible on a tree trunk is only the temporary reproductive structure of a much larger organism. The main body of the fungus is a vast, hidden network of thread-like cells called the mycelium, which lives inside the wood. This mycelium is composed of microscopic filaments called hyphae, which penetrate the substrate to absorb nutrients.
The fungal hyphae secrete potent digestive enzymes directly onto the wood, pre-digesting the complex plant material outside of their bodies. These enzymes break down rigid cell walls, allowing the fungus to absorb the resulting simpler molecules. The mycelium can reside in various locations, including the outer bark, inner heartwood, or surrounding root substrate, depending on the species.
When environmental conditions are favorable, typically involving sufficient moisture and a drop in temperature, the mycelium forms the visible mushroom, known as the fruiting body. This structure produces and releases billions of spores into the air, which are the fungal equivalent of seeds. The mushroom’s location marks the point where the underlying mycelial network is reproducing.
Common Examples of Tree-Dwelling Mushrooms
Many common fungi that grow on trees are classified as polypores, recognized by their shelf-like or bracket-shaped fruiting bodies that lack gills.
Polypores
Species like Turkey Tail (Trametes versicolor) are small, thin, and velvety, often displaying concentric rings on dead wood. Other polypores, such as the woody Reishi (Ganoderma species), grow in a distinctive kidney shape on hardwood trunks.
Cap Fungi
Oyster mushrooms (Pleurotus species) are a cap fungus that typically grows in overlapping clusters on dead or dying deciduous trees like beech and poplar. These fungi are primarily saprobic, decomposing the wood they are attached to. They are easily identifiable by their short or absent stems and gills that run down the stalk.
Parasitic Fungi
Another frequent sight is the Honey Mushroom (Armillaria species), which forms dense clusters near the base of trees or on exposed roots. This fungus is a destructive parasite that causes root rot in living trees, often feeding on buried wood. Bracket fungi, like Chicken of the Woods (Laetiporus sulphureus), are vibrant, sulfur-yellow and orange shelf fungi that often indicate decay in the host tree.