On a recent hike I peeled off on a side trail for a view of the mountains from Piney Ridge, but was equally impressed by the lichen-covered rocks I stood on.

Nature’s capacity for art is always astonishing. No photo or painting can capture the beauty of lichens. But what, exactly, are they?

According to an article on Mother Nature Network, lichens are a unique composite, the result of a symbiotic relationship among organisms from as many as three kingdoms, with the main partner being fungus.

The lichen fungi (kingdom fungi) cultivate partners that manufacture food by photosynthesis. Sometimes the partners are algae (kingdom protista) and other times cyanobacteria (kingdom monera), formerly called blue-green algae.

A study published in Science revealed that, in addition to fungus and algae, lichens also include yeast. This yeast appears in the lichen cortex and contains two unrelated fungi. Lichens are their own life form.

They are also incredibly abundant, found everywhere from temperate forests to icy cold tundra and from the tropics to deserts. They are the dominant vegetation on as much as 8% of the planet’s land, able to survive where many other plant species don’t stand a chance. Lichens are pioneers on a variety of surfaces including bare rock, sand, cleared soil, dead wood, animal bones, rusty metal and living bark.

They can survive extremes of heat, cold and drought. They do not feed off the surface on which they grow, as parasites do, but instead create their own food — thanks to their algae — through photosynthesis.

The main body of a lichen is called a thallus, which is described in three major categories: crusty, leafy and shrubby.

Scientists originally thought lichens were very early organisms, making their way from land to water to pave the way for plants. But a 2019 study found that they are much younger than originally thought.

Still, there are patches of lichens that are incredibly old. One species of lichen in Greenland is between 3,000 and 5,000 years old.

Lichens are slow-growing, just a few millimeters or less per year for many species. But with slow growth comes longevity, and as is usually the case with slow-growing organisms, they are some of the oldest living things on the planet.

Lichens have developed an incredible array of defenses, including an arsenal of more than 500 unique biochemical compounds that control light exposure, repel herbivores, kill attacking microbes and discourage competition from plants.

Among these compounds are many pigments and antibiotics that have made lichens useful to people in traditional societies.

According to Ohio State University, research with lichens suggests these organisms hold promise in the fight against certain cancers and viral infections, including HIV.

Unfortunately, the longevity of lichens is threatened by factory and urban air pollution. Even as humans threaten their existence, lichens are being used to quickly and cheaply assess levels of air toxins in Europe and North America.

We need to start listening to lichen, another organism warning about our failing natural world.

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