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Chances are, though, you’ve come face-to-face with plenty of these crusty, leafy, or shrubby growths. Lichens live on rocks, branches, houses, even metal street signs. You can find these often colorful organisms almost everywhere—from deserts to rainforests, Antarctica to Africa. They’ve survived trips to outer space, and some scientists suspect there might even be lichens on Mars.

“If you go into your backyard, you will definitely find a lichen somewhere,” says Imke Schmitt, a lichen researcher—called a lichenologist—at the University of Minnesota, Twin Cities.

What you probably don’t realize is that a lichen is more than a single thing. It is a thriving relationship between two different types of living organisms: a fungus and an alga. Neither of these organisms is a plant, so the lichen isn’t a plant either.

Different species of lichens can look very different from each other. Thorsten Lumbsch, a lichenologist at The Field Museum in Chicago, took photographs of two varieties of lichens—a rock lichen (above) and a spot lichen (below)—during a recent

Thorsten Lumbsch

Thorsten Lumbsch

Through photosynthesis, the alga harvests the sun’s energy to make food for the fungus, which provides a place for the alga to live. But the relationship is lopsided, Schmitt says, with algae caged like prisoners—even slaves—inside their fungal hosts.

Around the world, scientists have identified tens of thousands of types of lichens. At least as many probably still await discovery, says Thorsten Lumbsch, a lichenologist at the Field Museum in Chicago.

“Even in North America, there is a huge lack of knowledge” about lichen diversity and biology, Lumbsch says. “There’s a lot still to discover.”

As lichenologists continue to find new species of lichens, they are also working to understand how various species are related to one another. By putting together a lichen family tree, they hope to understand why so many different types of lichens have evolved in so many places around the world.

Most research involves attempts to understand basic facts about the organisms and their interrelationships. But researchers are also teaming up with lichens to monitor the health of the environment, among other applications.

Tough work

Studying lichens is rarely easy. Most species depend on very specific conditions, and scientists can rarely get them to grow in laboratories. This provides lichenologists a great excuse to travel around the world, scouting new specimens and insights.

Lumbsch, for one, makes several trips to Australia and South America each year. In the field, he searches for a group of crusty lichens that tends to be quite tiny—usually less than a few millimeters long. Finding samples takes patience and a trained eye.

“You have to look very closely,” Lumbsch says. “Usually, I know which species I’m interested in and which habitats they grow in. So, I go there and crawl on my knees on the forest floor with a hand lens.”

Like many lichenologists, Lumbsch (far right) travels all over the world to collect specimens. This photograph was taken on a research trip to India in January 2008.

Thorsten Lumbsch

Spotting lichens is challenging enough. Identifying them is even harder. Many species look exactly alike, even when they are only distant cousins. Closely related species, meanwhile, can live in totally different environments, or on opposite ends of the Earth. (One species, for example, is found only near both poles.)

When they’re done collecting samples, lichenologists bring their catch back to the lab. Under a microscope, the researchers classify samples by structure and color. Then, they grind specimens into a powder, from which they extract genetic material. These DNA molecules, which appear in all cells, make up genes, which determine how organisms look and work.

The more closely related two organisms are, the more similar their DNA will be. Comparing DNA from different species, then, can give scientists an idea of when each group split off from a common ancestor. Researchers use this information to build lichen family trees that depict kinship between species.

“Once we have these trees, we can ask a lot of interesting questions,” Schmitt says.

For example, family trees can help explain what the first lichens looked like, how they have evolved over time, and how far any given species has moved around the globe. Such insights should provide a window into our planet’s distant past. Some researchers think that lichens were the first organisms to live on land, long before plants evolved to do so.

“[Lichens] have an extremely long history,” Schmitt says. “This is what we are trying to uncover by building family trees.”

The work is slow going, she adds. “But we are beginning to see a picture emerging.”

Environmental police

Despite their reputation as scientific curiosities, lichens have a practical side. Throughout history, people have used different species to make dyes for fabrics, poisons for arrowheads, and “green”-smelling scents for perfumes. Birds use lichens to make nests. Reindeer and other animals, including some people, eat them. (Don’t try this at home—some species taste awful!)

In modern times, scientists have found a new role for these growths: as environmental watchdogs.

Although lichens can live in some of the harshest environments on Earth, Schmitt notes that they “are very sensitive to any kind of change that humans put on the environment.”

Some species of lichen are highly sensitive to changes in the environment.

Tsnena/Wikipedia

Studies show that some species quickly disappear when exposed to air pollution. These sensitive types also suffer from habitat loss due to logging, construction, or other environmental disturbances. The presence of lichens in an ecosystem, then, generally signals that the air is clear and the environment healthy. Their disappearance, on the other hand, can be a warning sign.

Lichens are good monitors of air quality. In fact, studies have shown higher rates of lung cancer in people who live in areas where sensitive lichens have died off. As a result, Lumbsch says, some European cities require developers to confirm the presence of sensitive lichens as a sign of habitable air quality before building new homes. Where lichens reside, city planners can feel confident that homeowners will have good air to breathe.

Among other projects, Lumbsch and his colleagues are looking at the effects of climate changes on lichen populations. Some day, he says, lichens might add service as global-warming sentinels to their list of accomplishments.

Lichens have long been overlooked. Chat with a lichenologist, though, and you’ll find plenty about these underappreciated growths to like, if not love!

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Shitake mushroom.

Robert L. Anderson, USDA Forest Service, www.forestryimages.org

Scientists do all of these things—and more. Mushrooms belong to a major group of organisms called fungi. Not quite animals and not quite plants, fungi are turning out to be full of mysteries and surprises.

Mushrooms pop up in forests at certain times of year in various places all over the world and then disappear completely without warning. Some are as big as a car. Others are too small to see without a magnifier. Their colors range from bright orange to purple to green.

To add to the intrigue, it turns out that fungi are more closely related to animals than they are to plants—even though they look more like plants. Some types even seem to have ingredients that fight cancer, though others can kill you.

“Once you get to know them, they really become interesting,” says mushroom researcher David McLaughlin. More than just an ordinary mushroom lover, McLaughlin is curator of fungi at the Bell Museum of Natural History in Minneapolis. He’s also a professor at the University of Minnesota in St. Paul.

McLaughlin and other fungi experts estimate that between 1 million and 1.5 million species of fungi exist on Earth. Yet, only about 10 percent of them have been identified and named.

“It’s amazing how little is known,” he says, “and how much there is to discover.”

Filaments and spores

A few basic traits tie all fungi together. Most are made up of threadlike structures called filaments. They feed on dead and dying organisms. To reproduce, they send out spores instead of seeds. And the mushrooms that we see (and buy at the store) are just the fruits of fungi. Most of a fungus stays hidden underground.

This microscopic view of a fungus that grows on corn roots shows its threadlike filaments and spores (round bodies). This sample has been dyed so that it glows green to make it more visible.

Sara Wright, USDA Agricultural Research Service

Across the fungus kingdom, however, there’s a large amount of variety—in looks, lifestyle, and flavor. Some are delicious, while others are poisonous. Some grow on trees, while most grow on the ground.

To get a better idea of exactly what’s out there, McLaughlin and his coworkers are pulling together all the data published about mushrooms over the last 40 years. They’re also building large computer databases to hold the information they collect.

In the end, the researchers hope to piece together a fungal family tree. The tree should help explain how various types of fungi are related to each other and how different species developed over the course of evolution.

“We’re trying to fill in holes in the data so that people can understand how fungi evolved,” McLaughlin says.

There are also practical reasons for creating a fungal family tree. Hundreds of kinds of fungi cause diseases in people, including ringworm and athlete’s foot. Some 5,000 types cause diseases in plants. Understanding which species are related to one another allows researchers to predict which ones might cause diseases and which ones might respond to certain treatments. Also, knowing how much diversity is out there is the first step in knowing if and when certain species start disappearing.

Diversity and DNA

McLaughlin uses various features of fungi to put them into categories, starting with the shape, size, color, texture, smell, feel, habitat, and manner of growth of the fungus itself and details of its cells, fruiting bodies, spores, hairs, and other structures.

Other researchers use modern advances in technology to classify fungi. By comparing the genetic material DNA in two different species, scientists can determine how closely related these species are.

Chanterelle mushrooms.

Theodor D. Leininger, USDA Forest Service, www.forestryimages.org

In one recent study, McLaughlin says, researchers took samples of soil from high elevations in the Rocky Mountains. They found fungal DNA in the soil and were able to use it to identify an entirely new type of fungus.

Taking a closer look at mushrooms is also revealing how much more there is than meets the eye in the wide world of fungi. “With new techniques, we’ve been able to say, ‘Oh my. We thought these were the same things. But now that we look closer, we’re able to say they’re not the same thing,’” McLaughlin says. “Everyone assumes that if it’s shitake, it’s a shitake. Well, a shitake is not just one thing.”

The porcini group, too, appears now to include at least 35 species living across the Northern Hemisphere, not one or two species as previously thought. That’s important because people have been using porcinis as medicine for thousands of years. These mushrooms have also been getting attention lately for their ability to destroy tumor cells. It’s possible that not all types of porcinis provide the same benefits.

Mushroom specialist David McLaughlin is working with medical researchers to see if certain mushrooms can prevent cancer.

Photo by Tim Rummelhoff, University of Minnesota.

Unfortunately, most of the studies previously published about these mushrooms are useless now, McLaughlin says, because the scientists didn’t keep specimens of what they were looking at. It’s hard to tell exactly which particular type of mushroom they were studying.

Creating a new, large database will help researchers accurately classify the fungi they are working on. Having such specific information about these fungi will make their results more useful to other scientists.

So, the fungi hunt continues, whether it’s to learn more about these fascinating organisms or simply to identify something good to eat.

Be careful, however. Don’t eat any mushrooms that you find in the woods without checking with a teacher, parent, or mushroom expert first. Some mushrooms are poisonous enough to kill you.

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Word Find: Mushrooms