Samoa guide. 33. Fungi: the vital decomposers

Fungi fill a very important role in nature by breaking down dead organisms into their basic elements so those elements can be used again to build new organisms. This nutrient recycling is especially important in the tropics where organisms are born and die at a very fast rate. If it weren't for fungi, bacteria, and other small organisms that eat dead plants, dead trees and bushes would soon bury us.

WARNING! Many fungi are poisonous. Eating them can cause sickness or even death. Don’t eat any mushrooms unless you are certain they are safe.

We are usually aware of fungi only when they damage something. That’s because they live inside the things they are eating. Sometimes we see their white mycelium in rotted wood, but most often we don’t see them until they form "fruiting bodies". These fruiting bodies make thousands and thousands of spores that grow into new fungi wherever they land. Sometimes these spores are brightly colored, like the blue, green, or white mold on old food, or the black mold in the bathroom shower. Other times we find mushrooms, another kind of fruiting body, growing on the ground or from trees. Fruiting bodies are an indication that the insides of the trees are being eaten. These fungi may be thin and delicate, tough and rubbery, or hard as wood. The “ear fungus” (Auricularia) is brownish-purple, and thin like an ear, while the “tooth fungus” (Flavodon) is bright chartreuse with short tooth-like pores on which the spores are formed.

Most wood decay fungi are called conks, or shelf fungi. One of the most common “wood rotters” in American Samoa is the artist’s conk (Ganoderma australe). This fungus grows out from the tree in the shaped of a fan. It has a light brown top that is sometimes dusty with spores from the conks above it, and a whitish-gray lower surface. The gray surface looks smooth but is actually made up of thousands of very small pores, inside of which the spores are formed. If this pore surface is lightly scratched, a brown line remains, and for centuries people have left messages or drawn pictures on them, hence their name, “artist’s conk”.

People used to think fungi were a kind of plant and placed them in the plant kingdom. But fungi are so different from any other organism, they were given their own kingdom. Most fungi (except yeasts and a few others) are made up of many cells arranged in long strands called hyphae. All the hyphae together make up the mycelium, or body of the fungus. As the hyphae grow through their food, a plant for example, they release enzymes. These enzymes dissolve the plant cell walls and the fungus mycelium absorbs the nutrients from the plant.

Some fungi threaten our food supply. The black leaf streak disease of bananas (lausu lui, or black Sigatoka) is caused by a fungus (Mycosphaerella fijiensis) that you can only see through a microscope. It damages the banana leaves, making the fruit small and of poor quality. Farmers have to use special chemicals to control this disease, which cost them time and money. The taro leaf blight disease (lega) that killed most of the Samoan taro in 1993-1994 was caused by a water mold (Phytophthora colocasiae). We used to call water molds ‘fungi’, but scientific tests show they are more closely related to certain red algae. They have spores that swim and their mycelium is made of very different ingredients. Water molds are no longer in the kingdom Fungi, but have been placed in one of the new kingdoms, either Protoctista or Chromista.

The colorful lichens that grow on trees and rocks are actually fungi and algae living together. This type of relationship is called mutualism, where both organisms benefit from the relationship. In severe climates, the fungus protects the alga from damaging ultraviolet light and supplies water and dissolved minerals. The alga makes food for both organisms through photosynthesis. In other instances, this symbiosis could be considered parasitism. In American Samoa, many algae living on leaves or tree bark receive enough moisture and shade to exist without the help of a fungus. In fact, the fungus may actually damage or kill the algae.

What do leaf spots, beer, itchy feet, rotting trees, fresh bread, mold, and pizza have in common? Fungus! Different kinds of fungi (the pleural of fungus is fungi) can cause diseases in plants and humans, make alcohol and raise bread. Certain fungi (mushrooms) are cooked and eaten.

Fungi are sometimes used by Samoans to make fermented drinks, such as pulouaitu (ghost hat). This drink is made from mushrooms growing out of cattle dung that are boiled, strained, and drunk to cause an alcohol-like feeling. Alafa is an interesting forest mushroom (Mycena sp.?) that glows in the dark and has actually been used to illuminate or mark trails at night. Children also create a strange effect by sticking alafa on their faces. Several other unrelated organisms also produce this bioluminescence, or biological light, by metabolizing a chemical in their bodies called luciferin. Different organisms produce different colors of light: green for jellyfish, greenish-yellow for fireflies, red for railroad worms, and greenish-blue for glow worms and mushrooms. Scientists continue to study this light-producing process, which is extremely efficient (almost 90%).