March 10, 2018
All winter, I stared at my magnolia tree’s bare branches, wishing for spring. Except, when I looked closely, I saw that the branches weren’t bare. While I waited for green leaves and pink blossoms, I saw that silvery tufts and grey-blue rosettes like doilies on my grandmother’s armchair had adorned the branches and tattooed the trunks. Lichens.
Once I became aware of lichens, I saw them everywhere: In spots where nothing else thought to grow. On fences, trees and rocks. Green, blue, yellow, rust-colored, round, bumpy, hairy. Hanging down like a man’s long beard.
Are they parasites that suck life from a tree, I wondered. No, I learned. Lichens cling to branches; they don’t tap into a tree’s nutrients. All they need is light, moisture, clean air and freedom from competition. Are they plants? No. A fungus? Not entirely. Are they useful? Some are.
Reindeer survive by eating lichen. Other animals and people eat lichen, too. Some biochemical compounds in lichen are used for poisons and plant dyes, in medicine and perfumes. And, scientists track air quality with lichen. Like a canary in a coal mine, lichen die in polluted air.
Remarkably, lichens were likely among the first land-dwelling organisms on Earth. They range in size from a pinhead to crusts covering large areas to those drifting down 9 feet from a tree branch. But, even though an estimated 15,000 kinds of lichen live on the planet, scientists are still discovering exactly what lichen are.
At first lichen were classified as simple organisms. Then, microscopy revealed a symbiosis between two kingdoms. To form lichen, ascomycetes fungi from the Fungi kingdom associate with a photosynthesizing partner — algae in the Protista kingdom and/or cyanobacteria — aka blue-green algae — from the Monera kingdom. But recently, scientists learned that lichen is not a duet between fungus and alga/cyanobacteria; it’s a ménage a trois.
In 2016, an Austrian lichenologist, Toby Spribille, discovered a surprising third symbiotic partner. He was trying to understand how two species of lichen made from the same fungus and alga could be so different. Both look like Spanish moss, but Bryoria tortuosa is yellow and poisonous while Bryoria fremontii is brown and edible. When Spribille and University of Montana biologist John McCutcheon looked deep into the lichens’ genetics, they discovered genes belonging to basidiomycetes. Basidiomycetes are most known for making mushrooms, but in lichen are yeast, obscure fungi called Cyphobasidium. They grow as single cells rather than as, with brewer’s and baker’s yeast, a chain of cells in filaments. The scientists then discovered the same yeast living in lichens on six continents. The yeast had been hiding for centuries.
In lichen, the alga or cyanobacteria feeds the fungus by converting energy from the sun through photosynthesis into vitamins and simple carbohydrates. For its part, the fungus absorbs water vapor and the carbohydrates, transforms them into different carbohydrates and provides shelter. That’s the symbiosis.
To form a lichen, the fungus creates a composite body called a thallus to house the alga, and creates hair-like growths called rhizines or a central peg to anchor the thallus to a substrate. (Rhizines and central pegs aren’t roots; they have no vascular capabilities.) The yeast, which is embedded in the lichen cortex (skin), likely produces protective chemicals. Thus protected, algae can inhabit many different environments, while quietly turning carbon dioxide into oxygen.
Lichen grow slowly and many don’t like to be disturbed. There are more than 100 lichen species in Marin, with the widest variety in Point Reyes, but if you collect, do so judiciously and never an endangered species. Once brought inside, lichen die. Lab scientists haven’t managed to grow lichen, and botanists aren’t sure how lichen reproduce. Perhaps a piece breaks off and begins a new growth, or fungus spores find new alga.
So, I plan to enjoy the two lovely species decorating my magnolia tree right where they are and never again think the branches are bare.