Saturday, January 23

Fungus Among Us


As the winter season brings rain to the redwood forest, the soil comes alive. Banana slugs appear en-mass, newts emerge from their summer sabbaticals, and earthworms wiggle their way up to the surface. Upon reaching saturation, the earth itself appears to explode with odd domes, humps, clusters, shelves, and various other forms of fungal flesh. Mushroom season is upon us. Ubiquitous representatives of the unseen underworld, mushrooms are seemingly everywhere in the Santa Cruz Mountains in the winter; a person can hardly step without crushing one back into the soil.

Technically speaking, mushrooms are the visible fruiting bodies of fungi; and as fungi, they are placed in their own kingdom. Prior to molecular analysis, all fungi were placed in the Plantae kingdom, but in 1969 they were rightfully recognized as being markedly different from the earth’s plants. Thus began the five-kingdom system of taxonomy, with the addition of the newcomers, the fungi. Fungi are now believed to be more closely related to animals than to plants, having diverged more recently from their evolutionary branch with Animalia.

The fungus kingdom is incredibly diverse, and includes the largest living organism on earth (a colony of honey mushrooms in Eastern Oregon covering over 2,000 acres) as well as some of the smallest (single-celled chytrid fungi responsible for the amphibian disease chytridiomycosis). And it is fungi that create the many mushrooms we see dotting the forest floor. In order to reproduce sexually, a fungus must somehow spread its spores. Mushrooms provide a convenient, sheltered way to do so – they pop up, open, and poof! Spores are sent flying through the air.

If categorizing based on their ‘feeding’ habits, there are three major groups of mushrooms – saprotrophic, obtaining nutrients from dead organic matter; parasitic, obtaining nutrients from living organic matter, and mycorrhizal, which form a symbiotic relationship with plant roots. Here in Henry Cowell Redwoods, we have a great variety of mushroom-bearing fungi, and can see all three of these categories in a short stroll across the park. 

 Tree oysters on a coastal live oak
 
An example of a saprotrophic mushroom is the tree oyster (Pleurotus ostreatus), which grows on dead or decaying wood. This fungus will invade dead logs with its mycelium, stretching throughout the wood and absorbing nutrients. When moisture conditions are right, the fruiting body appears as a large white shelf mushroom growing from the side of its host log. It may be spotted growing on dead tan-oak and [dead] live oak throughout the park. The tree oyster is also commercially cultivated as an edible mushroom, and is available in many grocery stores.



 Honey mushrooms sprouting from the base of a tan-oak
A well-known parasitic mushroom is the honey mushroom (Armillaria ostoyae), which grows on the roots or near the base of living trees. This fungus attacks living trees, growing into their sapwood and eventually killing them. The telltale sign is, of course, a cluster of honey mushrooms sprouting from the tree or nearby ground. This species is the aforementioned largest living organism in the world by biomass. Honey mushrooms may be spotted throughout the park parasitizing Douglas-fir trees, a common host. They typically grow in clusters, are golden-brown (hence the name), and usually have a white ring around their stalk.
Butter bolete (Boletus appendiculatus) growing from the roots of a tan-oak.

Most mushrooms fall under the third category - mycorrhizal. These fungi form a symbiotic relationship with the roots of plants, growing around the roots and sometimes even inside of them. The fungus and the host plant can exchange nutrients and water, and both benefit from the relationship. In fact, eighty percent of terrestrial plants have a mycorrhizal fungal partner. Examples of this category include the boletes (Boletus species), a genera containing many large, handsome mushrooms. Boletes often associate with madrone, oak, and Douglas-fir, and may be spotted throughout the park growing within the root zone of their host tree. Boletes are typically bulbous, with a brownish cap, a massive, thick stalk, and pores rather than gills under the cap.

Regardless of their feeding habits or growth forms, for many folks a mushroom is just a mushroom – save for the kind you have in pasta and on pizza (Agaricus bisporus). But what our fungal friends do just under the surface of the soil is pivotal for the health of the forest, and perhaps for the health of the entire terrestrial earth. So the next time you’re out for a walk in the park, enduring the bleakness of the coastal winter, stop and take a closer look at those strange things beneath your feet. You might be surprised. 

[originally published in Words of the Woods, the newsletter of Henry Cowell Redwoods State Park - January 2010]

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