Lichens—they’re everywhere. I recently traveled to the temperate rainforest of the Oregon coast and was intrigued with the profusion of lichens that grace this area. But you don’t need a rainforest to support lichens. Some 478 species of lichens live in Iowa, lots of them on Owl Acres. Lichens are often mistaken for moss, but in fact they are not plants at all.
So what exactly is a lichen anyway? Lichens are an intriguing example of symbiosis—organisms living together in specific ways so that each one benefits from the relationship. In the case of lichens, the primary member of the little family is a fungus. The most common types of fungi in lichen relationships are Ascomycetes or cup fungus. The fungus forms a cup-shaped structure which serves as the body of the lichen. The fungus partners with either specific algae or, in some cases, cyanobacteria (also known as blue-green algae). Protected by the body, or thallus, its partners can grow and work without drying out. Their work is converting sunlight, water and carbon dioxide into sugar.
Now the fungus gets fed, and the algae or bacteria get a stable, protected platform to live on and a continued source of moisture and minerals from the fungus. In cases where the cyanobacteria form the partnership, the fungus has an added advantage because the cyanobacteria can both photosynthesize and fix nitrogen. Lichens don’t look anything like either of the partners that form them. Instead, they act as a single organism. They even reproduce like a single organism by creating little packets of fungal spores and algae which they send out on the wind.
Lichens may also include other partners such as yeast cells. The yeast helps the lichen produce acids that protect the lichen from outside invaders.
Lichens can grow on just about anything. Rocks, glass, bark, wood, mosses, soil—any surface that is not disturbed. They absorb moisture from the air, so they don’t need a root system. They aren’t parasites, and use these surfaces just to grow on. Lichens take on three characteristic shapes. Crustus lichens form a crust that looks like paint. Folias lichens look like they have flattened leaves. Fruticus lichens stand erect like little trees and, in fact, are used in model train layouts to represent trees. Although a lot of them are some shade of green, others might be orange or black or yellow or even slate blue.
Estimates of the number of types of lichens world-wide range upwards of 18,000. Scientists classify them by their fungal partners, but there are some 40 genera of possible algal or bacterial partners to choose from. On Owl Acres, the most common lichens are found on tree bark. Two of the most common species include star rosette (Physcia stellaris) and hoary rosette (Physcia aipolia) lichens. They look very similar with whitish-gray to cream-colored bodies that are somewhat darker in the center. The thallus, or body, of the lichen is divided into lobes forming a rosette. Each one is about an inch and a half across, and they favor the bark of elm, alder and poplars in relatively open areas. They often merge with other lichens to form what looks like one big one.
People have used lichens for millennia for food, forage, medicine and dyes. Lichens are also little chemical factories, turning out over 400 different substances studied so far. Presumably these chemical substances are produced to protect the lichen from other microbes, and people have used some of them specifically for their antimicrobial concoctions.
Lichens have been used to make dyes for clothing and baskets, and today, one significant use of a dye from lichens is the dye used in litmus paper. It turns blue in low-acid solutions and red in high-acid solutions. Products from lichens are also used today in deodorants, perfumes toothpaste and salves.
Another aspect of lichens is that they are very sensitive to air pollution. They can be used as a bellwether to detect and evaluate air quality. If lichens are not present, air pollution may be the cause. On Owl Acres, our lichens are robust, so presumably our air quality is quite good.
Photo by Author. Alt text: Blue green lichen on walnut bark. The lichen is tight to the surface, like paint.