The next time you go for a hike in Highlands County, look down. You may see a jungle of tiny organisms no taller than your shoe: some puffy, some flat, some leafy, in various shades of green, grey, blue, and yellow. These are lichens! Often mistaken for a moss or mushroom, a lichen is a mutualism between two distantly related organisms, a fungus and algae. The fungus provides the body of the lichen while the algae allows the lichen to carry out photosynthesis like plants do. Lichens can cover much of the ground in scrub habitats throughout Florida and are an essential component of ecosystems, influencing plant growth as well as water and nutrient cycling.

“There are a diverse array of lichens in the Florida scrub, including about nine species in the genus Cladonia, which grow directly on the sand and litter, having no roots to anchor them, and so are sometimes called ‘vagrant lichens.’ They each have a unique form and subtle differences in the habitat they prefer,” says Dr. Sterling Herron, a research assistant in the Plant Ecology Program at Archbold Biological Station. Common names for lichens include “Jester Lichen,” “Cigarette Ash Lichen,” and “Spaghetti Lichen,” alluding to distinctive aspects of their appearance. The myriad shapes of lichens directly result from the unique combination of the algal and fungal species in the pair, which ceases to exist if they are separated.

Dr. Herron adds, “These Florida ground lichens are physiological tanks. They often become hydrated and soft in the morning when they photosynthesize. However, they become desiccated in the hot afternoon sun, repeating this cycle daily. Often having no means of sexual reproduction, lichens spread extremely slowly by vegetative growth, maybe gaining a few millimeters in a year. They are easily broken and can be dispersed by wind or animals until they reach another suitable location. In many cases, it can take decades for a thick ‘lichen mat’ to form.”

These lichens tell a story about the habitat, including the fire history of a particular location. In the long-term absence of fire, lichens can completely fill open sand gaps between shrubs, even dominating over plants in some cases. The presence of lichens can also indicate a lack of air pollution, as they are very sensitive to air particulates, which are absorbed readily into their sponge-like bodies.

Dr. Aaron David, Director of Plant Ecology at Archbold, notes, “Some of the rarest of our ground lichens are the Perforate Reindeer Lichen (Cladonia perforata) and Spaghetti Lichen (Cladonia subsetacea), both of which are adapted to dry, sandy ridges, often in rosemary scrub.” Archbold research into habitat requirements of the Perforate Reindeer Lichen has demonstrated that it is very sensitive to fire and needs adequate refuge areas to regrow following a burn. Researchers track all known Perforate Reindeer Lichen populations, and new populations continue to be discovered in our area. “What’s more,” said Dr. David, “we are just starting to unravel the complex puzzle of genetic diversity across its range!”

Photo: Sterling Herron.

Lichens are also helpful to both people and animals. Our own Cladonia evansii (the “Powderpuff Lichen”), which grows in the scrub, has historically been used to create tiny “trees” in model train sets. Cladonia species are also known as “Reindeer Lichen” for good reason – in boreal regions, they are a critical winter food source for reindeer and caribou. Lichens worldwide provide bird nesting material and food for many animals, including monkeys and Polar Bears! Historically, people have also used lichens as food, clothing, dye, medicine, and poison. Globally, lichens can colonize some of the most inhospitable places, ranging from the arctic tundra to the driest deserts. They can grow on bark, rocks, other lichens, and even living insects!

Dr. Herron concludes, “Lying somewhere in the twilight zone between plants and fungi, lichens remain a mysterious and critical component of Florida ecosystems, and for which we still have much to learn. While they may not steal the spotlight, the next time you notice lichens in the wild, take a moment to appreciate the astonishing biology that allows this unique symbiosis to exist.”