By Anita Sanchez

Once you start look­ing, you notice them almost every­where you walk. On trees. On rock walls. On stumps and tomb­stones and trees. They look like blotch­es of gray­ish-blue or yel­low-green paint spat­tered in odd places: the dried-up, twist­ed forms of lichens.

What is a lichen, any­way? It’s actu­al­ly two things, two dis­tinct and unre­lat­ed organ­isms — a species of fun­gi and a species of algae — liv­ing togeth­er in a sym­bi­ot­ic rela­tion­ship. It’s not that the fun­gi and the algae hap­pen to be grow­ing in the same place — they actu­al­ly com­bine to form a whole new entity.

Lichens cling to sur­faces with things that look like roots, called hold­fasts. But hold­fasts aren’t roots, as they don’t suck up any nutri­ents or water — they just let the lichen hold on tight. The algae cre­ates food for both organ­isms, using sun, water, and air to make the sug­ars that nour­ish the pair of them. The fun­gus would starve with­out the algae’s photosynthesis.

But like any good rela­tion­ship, it’s a two-way street. The flim­sy, mois­ture-lov­ing algae wouldn’t stand a chance on dry, bar­ren rocks or tree bark with­out the sup­port and struc­ture of the fun­gus. The fun­gal cells sur­round the algae com­plete­ly — like an apple pie, so to speak, the crust being the fun­gus part, the fruit fill­ing being the algae. Espe­cial­ly after a rain, you can see the green gleam of the algae shin­ing through the thin fun­gus crust.

This inter­twined lifestyle gives lichens a tremen­dous advan­tage. They can sur­vive in the most inhos­pitable habi­tats you can imag­ine. There’s almost nowhere where lichens don’t grow — under the soil, on church steeples, on the back of a slow-mov­ing tor­toise. They’re a tiny touch of green in the Sahara. They’re the dom­i­nant species of veg­e­ta­tion in the Antarc­tic, where they live between snow crys­tals. They grow on the stone heads at East­er Island and on the top of Mount Mar­cy. Lichens espe­cial­ly love ceme­ter­ies. When you die, if you have a tomb­stone, there will prob­a­bly be a lichen grow­ing on it. 

There isn’t just one type of lichen: there are thou­sands of them, com­posed of var­i­ous com­bi­na­tions of algae and fun­gi. Dif­fer­ent species occu­py dif­fer­ent nich­es. For instance, a lichen that needs more sun­light might grow on top of a branch, while one that prefers mois­ture and shade might grow on the under­side of the same branch.

Most types of land plants have a waxy coat­ing called a cuti­cle on their leaves. This cov­er­ing func­tions almost like our skin, keep­ing mois­ture in and infec­tions out. Lichens don’t have this pro­tec­tive lay­er. Lack­ing a cuti­cle, lichens can absorb every speck of mois­ture before it trick­les away, a big advan­tage when liv­ing in an arid spot like the side of a boul­der. Lichens are essen­tial­ly liv­ing blot­ters that soak up every­thing they come in con­tact with. Unfor­tu­nate­ly for lichens, this includes pol­lu­tants in the air.

This per­me­abil­i­ty makes lichens high­ly sus­cep­ti­ble to air pol­lu­tion. Where smog and pol­lu­tants rise from cars and fac­to­ries, lichens vanish.

Sci­en­tists have been using lichens as handy, free bio-mon­i­tors since the 1800s. Lichens are the prover­bial canary in the coal mine. Like the dead canary, the absence of lichens is a cry of warn­ing, nature’s sub­tle smoke alarm.

As you wan­der the trails at Lan­dis, breathe deep! Here the air is fresh and clear. The lichens tell us so.

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Fall 2023

Volume 41 , Number 3

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