First in a series.

When I took biology in high school, I was taught that among living things, there were only two kingdoms: the animal kingdom and the plant kingdom. Mushrooms and various edible (and non-edible) fungi were included in the plant kingdom.

In recent years, scientists have classified fungi as a separate kingdom, so now, among living things, there are more than just two kingdoms. Bacteria and some single-cell organisms make up their own kingdoms, too, so there are at least five at this time.

Most people have had experience with fungi when they pull out a loaf of bread that has been sitting too long in the bread drawer or a piece of cheese or other item that has been hidden away in the back of the refrigerator for a couple of months.

Figure 1: Mold growing on a piece of bread.

We call this “mold,” which is one form of fungus. The usual response is one of revulsion and a vigorous effort to clean the area where the item was found.

While we might see some of the more unappetizing aspects of fungi, fungi are all around us and are critical to the entire ecosystem.

With our recent rains, fungi in the form of mushrooms start popping up all over, in our backyards and along the hiking trails in our local mountains.

Figure 2: Mold growing on an old piece of fruit.

Fungi have been included in their own kingdom because unlike animals and plants, their cell walls contain chitin. That is the same material that makes up the external skeleton of arthropods (insects, crustacea) as well as our finger and toenails.

The cell wall of plants contains cellulose, while the cell wall of animals is made up of cholesterol.

The term “fungus” comes from the Latin for what we now call mushrooms. The science of fungi is called mycology.

Figure 3: Mold growing on the plasterboard of a damp wall.

Fungi are found all over the world and an integral part of each ecological system. Except when they overgrow as in the two examples shown in Figures 1, 2 and 3 or manifest themselves as mushrooms – which are the reproductive body of specific fungi – they are usually invisible to us. They live in the soil as long thin strands called hyphae and are symbiotic with many plants and animals.

They can also be parasitic, depending on the species, so like everything else, there are good and bad fungi.

With respect to the plants, they can surround the roots and facilitate the intake of various nutrients from the soil. Indeed, without the fungi, some plants might not survive.

A classic mushroom growing in the field (photographed along the Canyon Trail in Placerita Canyon Natural Area). The ridges, in this case on the top of the cap are called gills and the spores are released from these areas.

They are also part of nature’s cleanup crew to break down dead material, both plant and animal, to return the nutrients to the soil to be used again by new plants and animals.

About 100,000 species of fungi have been formally described by mycologists, but it is believed this is only the tip of the proverbial iceberg and there are many more. As of 2011, it was estimated there were more than 5 million species, so clearly there are a lot still to be characterized and described with respect to their life history and ecologic role in the local environment where they are found.

As the fungal hyphae grow and coalesce, they become visible and are called mycelia. They will form on damp walls and spoiled food, where they are called molds, as part of nature’s clean-up crew, or become quite large with respect to their start, and then we see them growing on the bark of trees or sprouting from the soil and we call them mushrooms.

This mushroom was found one morning a few years ago in the writer’s backyard in Santa Clarita after a rain.

The usual mushroom is predominantly found only for a brief time, usually following a rain, and can be both fascinating and beautiful to look at closely. The mushroom cap sits on a stalk; it is the spore-bearing, fruiting body of the fungus, the part that in some cases can be eaten (but be careful) and that everyone recognizes as a mushroom.

So whether you are hiking along your local mountain trail or simply going into your backyard after a rain, keep your eyes peeled for mushrooms. When you see them, look at them closely, perhaps even using a magnifying glass, or take a photo so they can be enlarged on your computer screen, for they are intriguing.

They will not bite and they will not run away, but as soon as the area dries out, the mushroom cap will disappear and you will not be able to see the hyphae, which are microscopic in size and located in the ground.

The one caution is that while some mushrooms are delicious and eminently edible while others declare themselves to be poisonous, not all poisonous mushrooms have a distinctive appearance. If you are not an expert, do not pick any you find in the field to make your next mushroom omelet, soup, sauce, salad or pizza.

Paul A. Levine is a docent-naturalist at Placerita Canyon Nature Center and an avid butterflier.

Bracket mushroom growing on a tree trunk (photographed along the Canyon Trail in Placerita Canyon Natural Area).

Another bracket mushroom (also photographed in Placerita Canyon Natural Area).

This fascinating mushroom sprouted up in the leaf litter bordering the parking area near the Placerita Canyon Nature Center.

A view of the undersurface of the mushroom cap. Note the skirt-like collar around the stalk. This identifies this mushroom as poisonous but unless you are expert on mushrooms, you should not eat any that are found in the field, even those without the skirt. Those found in stores are safe to eat and are raised for food. The gills are also easily visible and as in this case, are usually on the underside of the cap. The spores are released from the gills.

Mushroom may come in a multiplicity of shapes, colors and forms. This one was photographed in the Sierra Nevada mountains growing out a dead tree stump.