Mosses, Lichens & Fungi

We often see what we think of as moss growing among tree branches, or we see a crusty, colored coating on the bark of trees or rocks. Sometimes we notice a greenish velvet carpeting on rocks, walls or trees, generally in regions not exposed to sunlight.

These interesting growths represent a significant portion of the plant world, a category that includes mosses, lichens and fungi (molds).

Mosses - There are nearly 15,000 species of mosses, so it is not easy to explain them with one simple description. They are typically small green plants that grow in clusters. They have no flowers or seeds, no vascular system to transport nutrients and water, and simple leaves that cover thin, wiry stems.

Mosses are often overlooked as plants, but they can provide a soothing appearance in a forest or wherever they are present. They can help prevent soil erosion, and they serve as a fertile base in which other plants can take root.

One of the most common mosses is sphagnum moss (peat moss), said to occupy nearly one percent of the earth's surface. Because many of its leaves and stems have large, porous walls, they can absorb large amounts of water. Peat moss is used not only as a fuel and soil conditioner, but also as a top dressing in flower arrangements and planter boxes.

Lichens - When we see lichens growing on trees, rocks and decaying wood, we think of them as plants, but they do not truly belong to the plant kingdom. They are a symbiotic combination of fungi and algae. Each of the many possible combinations produces a distinct species unrelated to either part. Lichens are plentiful, estimated to be the dominant vegetation on eight percent of the earth's land surface. When the two components combine, they undergo a transformation in appearance that is unique to each combination. Lichens often appear as variously colored crusty or scaly coatings on tree bark or rocks.

The fungal partner and the algae partner play complementary roles in lichen. The form is determined by the fungal partner, which is not capable of producing its own food. Hence the algal partner is left to be the "breadwinner." It feeds the combined plant by using sunlight to produce sugars and other carbohydrates. Many lichens also produce secondary compounds that are useful in making dyes and some primitive antibiotics.

Fungi - Fungi are plants that have no organized plant structure such as stems, leaves and roots. Yet they are one of the most successful organisms on earth. They exist everywhere—in the air, in water, on land, in our clothing—and there are more than 100,000 known species. They include yeasts, mildew, mushrooms and molds. With the exception of mushrooms, fungi are often collectively referred to as mold.

They do not fix their own nitrogen via photosynthesis as most plants do, but instead digest their food externally using the photosynthetic products of other plants for their metabolism. They propagate via spores and can survive in a dormant state for a long time.

Many fungi are hazardous to humans, producing diseases of the skin, hair, nails and internal organs. But many others are invaluable. For example, we use yeasts in bread making and wine fermentation, and other forms of fungi in medicines and cosmetics. Fungi are also responsible for much of the soil decomposition that leads to successful plant growth.

So the next time you run across some of these unusual "plants," whether hanging from tree branches or forming a smooth green carpet on the ground, you should have a different perspective on how they survive and how beneficial they are in our daily lives.