Lichens, working partnerships of fungi, green algae and in some cases, photosynthesizing bacteria, are all around us, but so unassuming that either you’ve never noticed them or passed them off as non-living objectoids. If you know lichens when you see them, you may have wondered if they’re truly alive. But alive they are, unlikely incorporations of mould, pond scum, and germs (fungi, algae and bacteria), some bringing with them a bizarre, alienesque beauty. Although often drab and cryptic, some lichens look like fluorescently colored, flattened, partly dried blobs of paint shot onto walls from paintball guns. Others bring to mind aerial views of multicolored forests on other planets. Some produce dreamlike forms, like tiny forests of cups mounted on stalks, or natural, multicolored mosaics and beadworks. “Lichen” in American English rhymes with “hikin’ ” while in British English, it rhymes with “kitchen.”
Eons ago, two, and in some cases three, fragile, squishy sorts of life-forms, fungi, algae, and cyanobacteria, worked out an alliance and a beneficial compromise. Fungi can’t make their own food; they can only live by parasitizing living things or digesting dead organic matter. Green algae and cyanobacteria can photosynthesize, using sunlight as a power source to drive their life functions.
According to the contract, the fungi build houses and apartment complexes, while the green algae live in them and pay rent by producing sugars for the fungus to consume as food. This is the basic and most common arrangement among lichen species: fungi supporting and protecting algae. In a few lichen forms, cyanobacteria are included in the contract. Cyanobacteria, formerly called “blue-green algae,” aren’t algae at all but strands of bacteria with the ability to photosynthesize. In lichens, cyanobacteria may take the place of the green algae or come onboard as roommates for the green algae. Cyanobacteria have a special, valuable talent: they can “fix” nitrogen, drawing it out of the air and converting it into chemical forms that other organisms can use. Lichens containing cyanobacteria benefit their ecologies by enriching the soil with their fixed nitrogen.
A lichen is something superior to its founders, a gestalt creature, a summary that’s more than the mere sum of its participants. Lichens are symbiotic: the two or three member species benefit from the relationship. They are also tough and almost immortal. The gnarly little fungal condo complexes, stuffed with algae and studded with cyanobacteria, far from being scabby scraps of papery or leathery somethings-or-other, are masterpieces of survival. They thrive in some of the world’s most inhospitable environments, ranging through forests, deserts, tundra, and rocky, treeless mountain heights. They can grow on nearly any surface, including rock, sand, dead wood, animal bones, rusty metal, living tree bark and even plastic. There are aquatic (fresh water) and even marine (ocean) forms, including a sort that grows only on barnacle shells. One species, recently discovered in Gabon in western Africa, lives only on certain species of plants that provide shelters for certain species of ants, and grows only on the roofs of the tiny, hollow ant shelters along the leaf’s midrib.
In a few harsh places, lichens are even the dominant organisms. Parts of the Namib Desert in southwestern Africa are naturally landscaped with reddish, shrubby lichens and nothing else. Lichens can survive centuries of intense heat, cold, aridity, or any combinations of these. Some desert species can dry out completely, through and through, then sit around, mummified, for long stretches of time. When rain falls again, the dry lichen scraps soak up water like sponges and become alive again.
Yet, hardy as they are, lichens are vulnerable to air pollution and acid rain. An abundance of lichens in an area is a sure indicator of clean air.
There are 14,000 known species of lichens on Earth, 4,000 in North America, and about 1,000 in New England. He Dr. Bernard Goffinet of the University of Connecticut’s Department of Ecology and Evolutionary Biology discovered a lichen species, never before recorded in new England, under the Uconn soccer bleachers in Storrs, Connecticut. Rain had leached tiny amounts of zinc from metal in the bleachers and left it in the soil beneath. The lichen species, able to tolerate the high zinc levels, got a foothold there and called it home. In Norwich, Connecticut, Dr. Goffinet found twelve lichen species growing on a single rock.
In New England, we’re most likely to see lichens as grayish-green, rounded, papery or leathery splotches seemingly pasted onto trees and rock surfaces. They’re perhaps most noticeable on gravestones, as gray, rounded patches, each up to a few inches wide, their appropriately creepy texture and color often competing for attention with the carved text and artwork. Lichens don’t sit well with people who work to care for gravestones, since lichens on stone surfaces gradually dissolve the surface of the stone with acids, to root themselves fast therein and to mine out nutrients. In time, most of a rock mass may be reduced to tiny flakes by this activity. Over long stretches of geologic time, lichens are significant soil producers.
There are four basic shapes favored by lichens: “crustose,” i.e., flat and crustlike, like the ones mentioned above that grow on gravestones; “squamulose,” mosaics of tightly packed, beadlike individuals; “foliose” or leaflike; and “fruticose,” shrublike and branching.
A several-organisms organism like a lichen has problems to solve as regards reproduction. How do you get the two or three member organisms to send out a combination of two or three fertile spores? Well, you don’t, or they don’t. Only the fungus reproduces sexually. If it’s a fungus that produces mushrooms as spore-dispersers, the sprouting mushrooms look no different than they would if the fungus grew alone. The fungal spores, scattered by the wind, are subject to chance, which determines, in its blind way, whether each spore lands or doesn’t land near free alga that it can hook up with for partnership. If the spore grows alone, it matures into a fungus all by itself, except in some lichen species whose fungal components can’t survive without an algal partner. If filaments growing from the fungal spore encounter algal cells of a species appropriate for that fungus species, the two will commence construction of a new lichen.
Many lichens have asexual, i.e., non-sexual reproduction strategies. The lichen may produce tiny bundles of algae cells neatly packaged in fungal fiber casings, called soredia, or the surface of a lichen may sprout tiny bags of mixed fungal and algal cells, called isidia, that seal themselves up and drop away. Genetically, these are clones, genetically identical to their parent organisms, thus missing out on the advantages of increased genetic variety arising from the reshuffling of genes that occurs in sexual reproduction. Yet, their overall chances of survival are better than those of the spores, most of which will die or become mere lichenless fungi.
Lichens are useful organisms for ecologies, wildlife, and people. Lichens enrich soils and serve as food and nesting material for wild animals. People have used lichens as sources of natural dyes. Lichens come nearly all colors, and the colors are biochemicals, nearly 500 types, that the lichens produce to control light exposure, discourage herbivores with foul tastes, fend off disease microorganisms and small invertebrates like slugs and insects, and taint the soil or rock surface beneath themselves to prevent other plants from establishing their species in the lichens’ ranges.
All in all, we see an impressive dossier of abilities and accomplishments of these ancient, often bypassed multi-organisms.