Lichens: A hid­den world

“Lichens are fungi that have dis­cov­ered agri­cul­ture” liche­nol­o­gist Trevor Goward

The Peterborough Examiner - - OPINION - Drew Monkman is a re­tired Peter­bor­ough teacher and co-au­thor of The Big Book of Na­ture Ac­tiv­i­ties. Reach him at dmonkman1@co­geco.ca. To see past col­umns, re­cent na­ture sight­ings and his other books, go to www.drew­monkman.com.

Of all the con­spic­u­ous or­gan­isms in the land­scape, lichens are prob­a­bly the most over­looked. They are not rare, but peo­ple who see and ap­pre­ci­ate them are few and far be­tween. The eye can­not see what the mind does not al­ready know. When you be­gin to pay at­ten­tion, how­ever, you will see lichens ev­ery­where, start­ing with those cu­ri­ous, crusty green patches on the bark of ma­ture maple trees on your street. In fact, the Kawarthas is home to hun­dreds of lichen species. With far fewer plants to com­pete for the eye’s at­ten­tion, winter is a great time to get to know these hard-to-clas­sify or­gan­isms.

Lichens are found in places where al­most no other or­gan­ism can survive. The type of sub­strate (sur­face) they grow on is of­ten the first step in iden­ti­fy­ing them. Some species flour­ish on the ground, which can in­clude bare soil, sand, hu­mus, rot­ting logs and stumps. Oth­ers make a liv­ing on sun­scorched rocks or cliff sides. Still other species pre­fer the bare bark and branches of de­cid­u­ous and conif­er­ous trees. Old trees of­ten have the most lichen di­ver­sity - the bark of a sin­gle sugar maple may har­bour a dozen species or more. The sub­strate’s only pur­pose, how­ever, is to pro­vide a sur­face to which the lichen can at­tach.

Bi­ol­ogy

Lichens are ac­tu­ally dual or even triple or­gan­isms, con­sist­ing of a fun­gus, an alga and/or a cyanobac­terium (blue-green al­gae) liv­ing to­gether as a sin­gle unit. The lat­ter two or­gan­isms - the “pho­to­bionts” - use sun­light to pho­to­syn­the­size glu­cose both for them­selves and for the fun­gus. Fungi are in­ca­pable of mak­ing their own food. In turn, the fun­gus pro­vides a home and pro­tec­tive cover for the pho­to­bionts, pro­tect­ing them from dam­ag­ing ul­tra­vi­o­let rays. This type of mu­tu­ally ben­e­fi­cial re­la­tion­ship in na­ture is called sym­bio­sis.

Although lichens are presently clas­si­fied as part of the fungi king­dom, this is only a clas­si­fi­ca­tion of con­ve­nience. Al­gae be­long to the pro­tista king­dom, while cyanobac­te­ria are in the mon­era king­dom. In this re­spect, lichens are as much tiny ecosys­tems as they are in­di­vid­ual or­gan­isms.

If you look at a cross­sec­tion of a lichen body (thal­lus) through a 10x hand lens, you will find a pro­tec­tive outer skin (cor­tex) of fun­gal cells. This cov­ers the pho­to­biont layer of sin­gle-celled al­gal and/ or cyanobac­te­ria cells, which are mixed in among branch­ing fun­gal fil­a­ments (hy­phae). Fi­nally, there is a third layer made up strictly of hy­phae. Although lichens have no roots, they do have fun­gal strands called rhizines that at­tach the un­der sur­face of the lichen to the sub­strate.

Lichens are clas­si­fied by the type of fungi they con­tain - usu­ally a species in the as­comycete group. These fungi lack the typ­i­cal mush­room cap and stalk and will only grow in a “lich­enized” state. In other words, they can only survive when liv­ing in tan­dem with al­gae and/or cyanobac­te­ria. They rep­re­sent about a quar­ter of all fun­gal species. Con­versely, the al­gae and cyanobac­te­ria in lichens can live on their own. Many ex­perts now re­fer to lichens as lich­enized fungi or, more po­et­i­cally, “fungi that have dis­cov­ered agri­cul­ture.”

Growth forms

Lichens have been di­vided into three sub­groups, based on dif­fer­ences in growth form. Fo­liose lichens (e.g., Rock Tripe) look some­what like leaves and of­ten have cup-like fruit­ing bod­ies (apothe­cia) that pro­duce spores. Fru­ti­cose lichens (e.g., Rein­deer Lichen) re­sem­ble shrubby or bushy growths, which stand up­right or hang from branches. Crus­tose lichens (e.g., Dust Lichen) of­ten bring to mind paint or pow­der sprayed on a tree or rock.

When and where

Lichens can be seen year-round, even now in the depth of winter. They survive the cold by dry­ing out to the point of be­com­ing brit­tle. If tem­per­a­tures climb above freez­ing, how­ever, and if suf­fi­cient mois­ture be­comes avail­able, pho­to­syn­the­sis can take place and the lichen will even grow.

Be­cause the Kawarthas over­laps two phys­io­graphic re­gions the Cana­dian Shield to the north and the St. Lawrence Low­lands to the south - we en­joy es­pe­cially rich lichen di­ver­sity. Each re­gion of­fers dif­fer­ent sub­strates, es­pe­cially in terms of ge­ol­ogy and tree species. For ex­am­ple, some lichens pre­fer to grow on lime­stone (south­ern Kawarthas), while oth­ers opt for gran­ite (north­ern Kawarthas). Some es­pe­cially good lichen habi­tats in­clude gran­ite ridges and conifer swamps (e.g., Pet­ro­glyphs Pro­vin­cial Park), lime­stone ridges (e.g., War­saw Con­ser­va­tion Area) and hard­wood stands with large sugar maples (e.g., Mark S. Burn­ham Pro­vin­cial Park). Even Peter­bor­ough it­self of­fers great lichen view­ing. Look for them on old brick walls, grave­stones, roofs and the trunks of ma­ture trees.

A few to know

A word of warn­ing. It is not al­ways easy to iden­tify lichens to the species level. In many cases, you will have to be sat­is­fied in rec­og­niz­ing the genus (the first word in the sci­en­tific name) or the group (e.g. shield lichens). Ex­perts of­ten use colour tests to be cer­tain of the species. They drop a reagent on the thal­lus and look for a spe­cific colour change.

On tree bark, the most ob­vi­ous species are usu­ally the fo­liose shield lichens like Com­mon Green­shield (Flavoparmelia ca­per­ata). It has pale-green lobes with a black lower sur­face and re­sem­bles a thin, flat, leafy cir­cle. A sim­i­lar species is Ham­mered Shield Lichen (Parmelia sul­cata). This fo­liose lichen has blue-gray lobes with a dis­tinc­tive pat­tern of white cracks on the sur­face. It is pol­lu­tion­tol­er­ant and eas­ily found on the bark of city trees. A crus­tose species to look for is Dust Lichen (Lepraria lob­i­f­i­cans). It is yel­low­ish-green to pale mint in colour and re­sem­bles paint or dust on the bark. Com­mon fru­ti­cose lichens in­clude the var­i­ous species of beard lichens (Us­nea species). Bristly Beard (Us­nea hirta) is very com­mon on the branches of conif­er­ous trees and birch. It has yel­low­ish-green, densely branched, erect stems. Other species lit­er­ally look like a beard hang­ing from a branch with hairs up to 40 cm in length. Many grow on spruce trees.

On rocks, watch for dif­fer­ent rock tripes (Um­bili­caria species), which are fo­liose lichens. They of­ten re­sem­ble dark, leath­ery leath­ery let­tuce leaves. Smooth Rock Tripe (Um­bili­caria mam­mu­lata) grows on steep rock walls and boul­ders in forests. It has red­dish-brown lobes and grows from a cen­tral stalk. The lower sur­face is pitch black. Cin­der Lichen (Aspi­cilia cin­era) is a com­mon crus­tose species. It has an ashy-gray, cracked sur­face with mul­ti­ple black spots. On lime­stone and lime­stone grave­stones, you might come across other crus­tose lichens called fire­dots (Calo­placa species). De­pend­ing on the species, they are yel­low or orange in colour. Side­walk Fire­dot (Calo­placa feracis­sima) is com­mon on lime­stone, in­clud­ing grave­stones.

On ground sub­strate, you may come across the best known and most eas­ily iden­ti­fi­able of all the lichens, namely Bri­tish Sol­diers (Clado­nia cristatella). This fru­ti­cose species is named for its re­sem­blance to the uni­forms worn by English sol­diers dur­ing the Rev­o­lu­tion­ary War. Look for green­ish-grey stalks, topped with bright crim­son red caps (the spore­pro­duc­ing apothe­cia). Another fru­ti­cose species, Trum­pet Lichen (Clado­nia fim­bri­ata) of­ten grows along­side Bri­tish Sol­diers. The grey-green thal­lus stands about 20mm tall with a dis­tinc­tive trum­pet or golf tee shape. Rein­deer lichens (Clad­ina species), too, grow on the ground and be­long to the fru­ti­cose group. They re­sem­ble tiny white, grey or green­ish shrubs or co­ral with nu­mer­ous branches. You can some­times find three or four Clad­ina species in a sin­gle clump. Car­pets of Clad­ina can cover huge ar­eas. A com­mon fo­liose genus, the pelt lichens (Peltig­era species) have semi-erect, grey-green to brown­ish lobes and su­per­fi­cially re­sem­ble rock tripe.

Ap­pre­ci­a­tion

Lichens are im­por­tant in many ways. Ruby-throated Hum­ming­birds use shield lichens (Parmelia) to cam­ou­flage their nests; deer, moose, cari­bou and even fly­ing squir­rels eat lichens; and tree frogs take ad­van­tage of the cam­ou­flage lichens pro­vide. In­dige­nous peo­ples still use lichens as dyes for crafts and other ar­ti­facts.

By de­grad­ing rock sur­faces and pro­vid­ing a site where or­ganic ma­te­rial can col­lect, lichens are the pri­mary col­o­niz­ers of bar­ren land­scapes such as rocks. As the lichen grows, these pro­cesses speed up and oc­cur over an ev­er­ex­pand­ing area. Even­tu­ally, mosses, grasses or ferns may take root in the mod­est ac­cu­mu­la­tion of soil and re­place the lichen.

The de­gree of lichen di­ver­sity in a given area is also a good “bio-in­di­ca­tor” of the amounts of cer­tain pol­lu­tants in the air. Some lichens are es­pe­cially sen­si­tive to sul­fur diox­ide. Part of the rea­son for this in­tol­er­ance is their ex­treme ef­fi­ciency in ac­cu­mu­lat­ing chem­i­cals (such as sul­phur) from trace lev­els in the at­mos­phere. Sul­phur de­stroys the chloro­phyll in the al­gal cells, which in­hibits pho­to­syn­the­sis and kills some lichens. It is there­fore pos­si­ble to es­ti­mate the amount of sul­fur diox­ide in the air by ob­serv­ing the num­ber and type of lichens grow­ing in an area.

An ex­treme ex­am­ple of a lichen’s abil­ity to absorb mat­ter from the at­mos­phere was seen in north­ern Scan­di­navia af­ter the Ch­er­nobyl nu­clear dis­as­ter. Rein­deer lichen ac­cu­mu­lated so much ra­dioac­tiv­ity that rein­deer feed­ing on it were con­sid­ered un­fit for hu­man con­sump­tion.

Maybe the most im­por­tant rea­son to ap­pre­ci­ate lichens, how­ever, is for their beauty. Take time to look at them through a good 10x hand lens. A beau­ti­ful world will be re­vealed. My favourite is the colour con­trast be­tween the frosted green stalks and the red tips of the Bri­tish Sol­dier lichen. Close-up pho­tog­ra­phy, too, is very sat­is­fy­ing. Put your dig­i­tal cam­era on a sturdy tri­pod and use the macro set­ting.

As for re­sources, I es­pe­cially rec­om­mend “Lichens of the North Woods” by Joe Walewski. “For­est Plants of Cen­tral On­tario” also has a small sec­tion on com­mon lichens.

A great on­line re­source is the lichens page of the USDA For­est Ser­vice web­site.

DREW MONKMAN/SPE­CIAL

A beard lichen is seen on a spruce tree.

DREW MONKMAN/SPE­CIAL

A species of cin­der lichen is seen on a snow-cov­ered rock.

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