British soldiers, a form of lichen, is often found on the ground, on dead wood, or among club mosses, showing its red spore-producing structures.
Photo: Kevin McKeon
By Kevin McKeon, Maine Master Naturalist
Plants, animals, fungi, algae and other organisms all have their distinct place in the world of living things. Generally speaking: Plants make their own food, animals and fungi eat other organisms, bacteria and protists (things like algae) eat both living and non-living things, and some also make their own food.
But what’s a lichen? It’s a combination of a plant (alga), and an animal-like thing (fungus). About nine years ago, scientists found two seemingly genetically identical lichens that displayed varying characteristics. One produced a toxic acid and the other didn’t. Studies uncovered that a third fungal component — a yeast — was present in most lichens. It’s a relationship manifested as a protective entity, shielding lichens against other destructive microbes, adding toxicity, and/or a bad taste. So, a plant, an animal, and a yeast combine to form lichens. Classification depends on their most obvious visual component — their fungal body.
A lichen begins to form when a fungal spore finds and captures a compatible species of algae. It then grows around the alga, forming the lichen body. The alga continues to photosynthesize food for itself, while the fungus robs some of this food for itself — effectively “farming” the alga, protecting it from harsh environmental conditions, and providing water and nutrients. This beneficial relationship is called symbiotic and is either mutual — when both species gain; communal — when one benefits while the other is unaffected; or parasitical — when one benefits while the other is harmed. The ongoing debate with lichens is which symbiosis applies: Is the alga being held captive, or is the alga enjoying a protective, productive life within the lichen? Julianna Rakowski, U.S. Fish & Wildlife Service Environmental Educator, describes this debate thus:
“The theories in place right now both agree that the fungal partner is benefiting from the algal partner by receiving the sugars that the algae can produce via photosynthesis. The argument comes in when determining whether the algae receive anything in return. Some scientists believe that the algal partner is benefiting by gaining favorable living conditions and having improved access to minerals. The other side states that only the fungal partner is favored, and that the stealing up to half of the sugars that the algae partner produces is more detrimental to the algae partner than if it were to be growing alone.”
Most lichenologists gravitate towards the position that algae can survive outside of the relationship, while fungi cannot — making the symbiosis parasitical, with the fungus parasitizing the alga. The issue remains debatable, yet another example where discovery demands further study.
There are three major types of lichen: foliose, fruticose, and crustose. Foliose are leafy lichens, with obvious upper and lower sides to their leaves, which can be flat, wavy, jagged, or bumpy. Fruticose are “shrubby” and can have erect stems that are either cupped, dangling like hair, or have long, thin leaves. Crustose lichens form crusts that appear painted onto their substrate, or underlying layer. They all attach to their substrate using thin filament-like hairs called rhizines, or by a stubby, central stalk called a holdfast. These “roots” do not feed the lichen; food comes from the air by absorption of mineral particles, water, trace chemicals, and pollutants from rain, dew, fog, and wind-blown dust. As it grows, the lichen’s rhizomes slowly penetrate the rock by creating pressure and secreting acids that dissolve and release minerals. (This is how soil is made, a story for later.)
Lichen has pharmaceutical uses, including antibiotics, laxatives, and treatment for respiratory and digestive issues, even rabies, tuberculosis, and AIDS. Lichens are in dyes and cosmetics. Deer, squirrels, voles, snails and people eat lichen. Many insects eat and live in them. Birds build nests with them.
Reproduction is via the fungal part and is accomplished sexually or vegetatively. Sexually, spores form a new fungus. If this newborn doesn’t “catch” another alga, it dies. Vegetatively, lichens can reproduce from fragments, i.e., cloning: A dislodged piece falls onto a suitable substrate — tree bark, rock, building, tombstone, plastic, cloth, soil — and grows.
Lichen emerged on Earth around 325 million years ago, but their diversity bloomed around 66 million years ago, after the fifth mass extinction event that did in the dinosaurs. Estimates vary, but there are at least 19,000 identified lichen species. In 2014, what was believed to be a single species turned out to be 126! Since hybridization is common among lichen-forming fungi, and with over 1.5 million fungi species, lichenologists give estimates of over 250,000 species. Individual lichens in the Arctic are estimated to be 8,600 years old; one on East Baffin Island about 9,500, and some in Alaska 11,500 years old — making them the oldest living organisms on Earth. Because lichen feed from the atmosphere, studying them enables tracking of past pollution levels and compositions. And lichen are tough creatures, surviving under simulated Martian conditions, and unprotected in outer space.
Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net.
The post Out in the Woods: Animal? Vegetable? No, Lichen! appeared first on Sanford Springvale News.
