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What kind of lichen is it (no. 2)?

What kind of lichen is it (no. 2)?


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I think i found very interesting lichen. I discoved it at 1.15 PM CET in Prague nature conservation area called Divoka Sarka.

I took this picture on the place of my discovery.

One piece of this specious had cca. 6 cm. And it look like a shrub. And this is micro photograf with magnification about 200X.


This is a fruiticose lichen, meaning one with a bushy growth habit. They are common in my native state of Texas (USA), where they hang off of oak trees. Your photos look much like them. I have seen other examples in the rainforests of the Pacific Northwest, in both Oregon and Washington. I can't name the species.

In the upper left of your first photo, I see a thick, stem-like structure. This looks to me like the holdfast, the place the lichen attaches to the tree or other support.


How a Guy From a Montana Trailer Park Overturned 150 Years of Biology

Biology textbooks tell us that lichens are alliances between two organisms—a fungus and an alga. They are wrong.

In 1995, if you had told Toby Spribille that he’d eventually overthrow a scientific idea that’s been the stuff of textbooks for 150 years, he would have laughed at you. Back then, his life seemed constrained to a very different path. He was raised in a Montana trailer park, and homeschooled by what he now describes as a “fundamentalist cult.” At a young age, he fell in love with science, but had no way of feeding that love. He longed to break away from his roots and get a proper education.

At 19, he got a job at a local forestry service. Within a few years, he had earned enough to leave home. His meager savings and nonexistent grades meant that no American university would take him, so Spribille looked to Europe.

Thanks to his family background, he could speak German, and he had heard that many universities there charged no tuition fees. His missing qualifications were still a problem, but one that the University of Göttingen decided to overlook. “They said that under exceptional circumstances, they could enroll a few people every year without transcripts,” Spribille says. “That was the bottleneck of my life.”

Throughout his undergraduate and postgraduate work, Spribille became an expert on the organisms that had grabbed his attention during his time in the Montana forests—lichens.

You’ve seen lichens before, but unlike Spribille, you may have ignored them. They grow on logs, cling to bark, smother stones. At first glance, they look messy and undeserving of attention. On closer inspection, they are astonishingly beautiful. They can look like flecks of peeling paint, or coralline branches, or dustings of powder, or lettuce-like fronds, or wriggling worms, or cups that a pixie might drink from. They’re also extremely tough. They grow in the most inhospitable parts of the planet, where no plant or animal can survive.

Lichens have an important place in biology. In the 1860s, scientists thought that they were plants. But in 1868, a Swiss botanist named Simon Schwendener revealed that they’re composite organisms, consisting of fungi that live in partnership with microscopic algae. This “dual hypothesis” was met with indignation: It went against the impetus to put living things in clear and discrete buckets. The backlash only collapsed when Schwendener and others, with good microscopes and careful hands, managed to tease the two partners apart.

Schwendener wrongly thought that the fungus had “enslaved” the alga, but others showed that the two cooperate. The alga uses sunlight to make nutrients for the fungus, while the fungus provides minerals, water, and shelter. This kind of mutually beneficial relationship was unheard-of, and required a new word. Two Germans, Albert Frank and Anton de Bary, provided the perfect one—symbiosis, from the Greek for “together” and “living.”

When we think about the microbes that influence the health of humans and other animals, the algae that provide coral reefs with energy, the mitochondria that power our cells, the gut bacteria that allow cows to digest their food, or the probiotic products that line supermarket shelves—all of that can be traced to the birth of the symbiosis as a concept. And symbiosis, in turn, began with lichens.

In the 150 years since Schwendener, biologists have tried in vain to grow lichens in laboratories. Whenever they artificially united the fungus and the alga, the two partners would never fully recreate their natural structures. It was as if something was missing—and Spribille might have discovered it.

He has shown that the largest and most species-rich group of lichens are not alliances between two organisms, as every scientist since Schwendener has claimed. Instead, they’re alliances among three. All this time, a second type of fungus has been hiding in plain view.

“There’s been over 140 years of microscopy,” says Spribille. “The idea that there’s something so fundamental that people have been missing is stunning.”

The path to this discovery began in 2011, when Spribille, now armed with a doctorate, returned to Montana. He joined the lab of symbiosis specialist John McCutcheon, who persuaded him to supplement his formidable natural-history skills with some know-how in modern genetics.

The duo started studying two local lichens that are common in local forests and hang from branches like unruly wigs. One is yellow because it makes a strong poison called vulpinic acid the other lacks this toxin and is dark brown. They clearly look different, and had been classified as separate species for almost a century. But recent studies had suggested that they’re actually the same fungus, partnered with the same alga. So why are they different?

To find out, Spribille analyzed which genes the two lichens were activating. He found no differences. Then he realized that he was searching too narrowly. Lichenologists all thought that the fungi in the partnership belonged to a group called the ascomycetes—so Spribille had searched only for ascomycete genes. Almost on a whim, he broadened his search to the entire fungal kingdom, and found something bizarre. A lot of the genes that were activated in the lichens belonged to a fungus from an entirely different group—the basidiomycetes. “That didn’t look right,” McCutcheon says. “It took a lot of time to figure out.”

At first, the duo figured that a basidiomycete fungus was growing on the lichens. Perhaps it was just a contaminant, a speck of microbial fluff that had landed on the specimens. Or it might have been a pathogen, a fungus that was infecting the lichens and causing disease. It might simply have been a false alarm. (Such things happen: Genetic algorithms have misidentified plague bacteria on the New York subway, platypuses in Virginia tomato fields, and seals in Vietnamese forests.)

But when Spribille removed all the basidiomycete genes from his data, everything that related to the presence of vulpinic acid also disappeared. “That was the eureka moment,” he says. “That’s when I leaned back in my chair.” That’s when he began to suspect that the basidiomycete was actually part of the lichens—present in both types, but especially abundant in the yellow toxic one.

And not just in these two types, either. Throughout his career, Spribille had collected some 45,000 samples of lichens. He began screening these, from many different lineages and continents. And in almost all the macrolichens—the world’s most species-rich group—he found the genes of basidiomycete fungi. They were everywhere. Now he needed to see them with his own eyes.

Down a microscope, a lichen looks like a loaf of ciabatta: It has a stiff, dense crust surrounding a spongy, loose interior. The alga is embedded in the thick crust. The familiar ascomycete fungus is there too, but it branches inward, creating the spongy interior. And the basidiomycetes? They’re in the outermost part of the crust, surrounding the other two partners. “They’re everywhere in that outer layer,” says Spribille.

Despite their seemingly obvious location, it took around five years to find them. They’re embedded in a matrix of sugars, as if someone had plastered over them. To see them, Spribille bought laundry detergent from Walmart and used it to very carefully strip that matrix away.

And even when the basidiomycetes were exposed, they weren’t easy to identify. They look exactly like a cross section from one of the ascomycete branches. Unless you know what you’re looking for, there’s no reason why you’d think there are two fungi there, rather than one—which is why no one realized for 150 years. Spribille worked out what was happening by labeling each of the three partners with different fluorescent molecules, which glowed red, green, and blue respectively. Only then did the trinity become clear.

“The findings overthrow the two-organism paradigm,” Sarah Watkinson, from the University of Oxford, says. “Textbook definitions of lichens may have to be revised.”

“It makes lichens all the more remarkable,” Nick Talbot, from the University of Exeter. adds. “We now see that they require two different kinds of fungi and an algal species. If the right combination meet together on a rock or twig, then a lichen will form, and this will result in the large and complex plant-like organisms that we see on trees and rocks very commonly. The mechanism by which this symbiotic association occurs is completely unknown and remains a real mystery.”

Based on the locations of the two fungi, it’s possible that the basidiomycete influences the growth of the other fungus, inducing it to create the lichen’s stiff crust. Perhaps by using all three partners, lichenologists will finally be able to grow these organisms in the lab.

In the Montana lichens that Spribille studied, the basidiomycete obviously goes hand in hand with vulpinic acid. But is it eating the acid, manufacturing it, or unlocking the ability to make it in the other fungus? If it’s the latter, “the implications go beyond lichenology,” Watkinson says. Lichens are alluring targets for “bioprospectors,” who scour nature for substances that might be medically useful to us. And new basidiomycetes are part of an entirely new group, separated from their closest known relatives by 200 million years. All kinds of beneficial chemicals might lie within their cells.

“But really, we don’t know what they do,” McCutcheon says. “And given their existence, we don’t really know what the ascomycetes do, either.” Everything that’s been attributed to them might actually be due to the other fungus. Many of the fundamentals of lichenology will need to be checked, and perhaps rewritten. “Toby took huge risks for many years,” McCutcheon says. “And he changed the field.”

But he didn’t work alone, Watkinson notes. His discovery wouldn’t have been possible without the entire team, who combined their individual expertise in natural history, genomics, microscopy, and more. That’s a theme that resonates throughout the history of symbiosis research—it takes an alliance of researchers to uncover nature’s most intimate partnerships.


Lichens: Symbiotic Association and Reproduction

Lichens are composite organisms consisting invariably of a fungus and an alga or a cyanobacterium. The two components are permanently associated with each other to form a lichen- body. The relationship is symbiotic. The algal or cyanobacterial component provides photosynthetic as well as products of atmospheric nitrogen fixation, if the partner is a cyanobacterium.

The fungal partner absorbs water and minerals from the substratum. The fungus also protects the photosynthetic component of lichen within a moist mycelial covering. The fungus sends haustoria into algal cells to draw nourishment. Thus, lichens represent an ideal example of symbiosis, in which two taxonomically separate organisms are permanently associated to form a single composite organism.

Only in a few lichens, it has been possible to separate the two partners and grow them independently. It has also been possible to synthesise a lichen by re-associating the original partners. When the two components are grown separately, the alga or cyanobacterium generally grows well in culture. But it is difficult to grow the fungal component. In nature, lichens are among the slowest growing organisms. There are about 25,000 species of lichens.

Lichens grow in greatly variable environmental conditions. Some can grow on solid rocks, while others in the permanently frosted arctic regions. However, majority of them prefer a moist humid shady environment such as one prevailing in the forests. In forests, lichens grow on the branches, barks and even on leaves of trees, as also on forest floors.

Lichens are often the first form of life to colonize a newly exposed rock or land. When they grow on solid rocks, they secrete organic acids which attack the rocky minerals causing weathering of rocks. This helps in genesis of soil, where subsequently plants can grow.

Lichens, though apparently insignificant in the overall biosphere, may be a considerable constituent in specialized geographical areas. For example, in the Tundra zones of Arctic regions, they form a major part of the vegetation. Cladonia rangiferina growing in such areas provides an important source of food for the reindeer and caribou. It is known as “reindeer moss”.

Certain lichens, like Cetraria islandica and Endocarpon miniatum, are used for human consumption. Leconera esculenta is also edible. Lichens have also other important uses. Rocella tinctoria is the source of erythrolitmin, an acid-base indicator dye which is the active ingredient of litmus. Lobaria pulmonaria and some species of Evemia are used as source of perfumes. Orcein, a dye used for staining chromosomes, is extracted from some species of Rocella. Usnic acid is obtained from Usnea species. It has antimicrobial activity. Letharia vulpine is a poisonous lichen.

Lichens are also of considerable importance as indicator organisms for detection of air pollution. Lichens can incorporate various cations into their thalli. The concentration of different cations in lichen thalli gives a measure of these cations in the atmosphere.

Moreover, certain lichens are specially sensitive to specific pollutants, like sulfur dioxide. By determining the species diversity in lichen population in an area, as well as by determining the disappearance of certain species at time intervals, it is possible to monitor the air quality.

Radioactive elements, like Cesium 137, escaping from nuclear plants, are absorbed by lichens. In the Chernobyl disaster occurring in the then U.S.S.R. in 1986, the reindeer population was found to have a much higher radioactivity, because they feed on radioactive lichens.

Symbiotic Association of Lichens:

In lichens, a photosynthetic component in the form of a green alga or cyanobacterium is permanently associated with a fungus, generally an ascomycetes and rarely a basidiomycete. Depending on the nature of the fungal partner, a lichen is designated as either an ascolichen or a basidiolichen. Some lichen-like forms do not have an algal component and they are called pseudo-lichens. Pseudo-lichens are mostly saprophytic or sometimes parasitic.

The photosynthetic component of a lichen is called a phyco-symbiont and the fungal component as myco-symbiont. The association always involves a single specific fungus and a single phyco- symbiont in any given species of lichen. The partners are not interchangeable which indicates that the symbiotic association is specific.

The phyco-symbionts may belong to about 30 different genera of algae and cyanobacteria. Among the algae, only green algae are components of lichen thallus. No other groups of algae are known to be present in lichens. The cyanobacteria may be unicellular or filamentous. The common unicellular cyanobacteria present in lichens are Chroococcus and Gloeocapsa.

Filamentous types include Nostoc, Scytonema, Rivularia, Stegonema etc. The green algae also include unicellular genera, like Chlorella, Cystococcus, Protococcus etc. or filamentous genera belonging to Chaetophorales, like Trentepohlia and Pleurococcus. Among the phyco-symbiont genera most commonly occurring in lichens are Trebouxia, Trentepohlia and Nostoc. These three genera are found in more than 90% of lichens.

The myco-symbionts of lichens are in the majority of cases members of ascomycetes belonging to the apothecia-forming group, called Discomycetes. Perithecia-forming ascomycetes (Pyrenomycetes) are rarely present in lichens (e.g. Dermatocarpori). Symbiotic association with basidiomycetes is also rare. The basidiolichens generally have some member of Thelephoraceae as myco-symbiont.

Some of the common ascolichens are Parmelia acetabula, Cladonia, rangiferina, Cetraria islandica, Usnea barbata, Lobaria pulmonaria, Rhizocarpon geographicum etc. Among basidiolichens, Cora pavonica is a well-known genus with Clavulinopsis is another genus with Clavaria as myco- symbionts. Some lichens found in India belong to the genera, Graphis, Lecanora, Parmelia, Physcia, Usnea, Cladonia etc.

An interesting aspect of lichen symbiosis is that certain chemical compounds are synthesized only when the phyco- and myco-symbionts are associated in a lichen. When the symbionts are separately grown, neither of the components is able to synthesise these compounds. Many lichens produce unusual phenolic compounds and lipids in substantial amounts in their thalli. Lichens are as yet not fully explored for obtaining new useful compounds.

Reproduction in Lichens:

Lichens may multiply vegetatively by fragmentation of the thallus. They also multiply by formation of several types of asexual structures. The most common of such structures are soredia. They are §mall globose deciduous bodies containing both the symbiotic partners. In these bodies, an algal or cyanobacterial cell is enveloped by fungal hyphae.

The soredia are formed on the surface of the thallus in very large numbers, giving a powdery appearance to the thallus surface. Soredia are easily detached by wind or splashing of rain drops. When they settle on a suitable substratum, they germinate to produce new thalli. Since both the symbionts are carried together in a soredium, the development of a new thallus is ensured (Fig. 5.30). The algal or cyanobacterial partners of lichen thalli generally multiply by cell division. Sometimes algae also multiply by formation of spores.

Sexual reproduction of lichens is restricted to the myco-symbiont only. The ascolichens produce asci and ascospores which are generally produced in well-differentiated ascocarps. As most of the ascolichens have Discomycetes, the ascocarps are commonly apothecia. Pyrenomycetes are much less common and so are perithecia.

Sometimes, defined fruit-bodies are-lacking and the asci are produced intermingled with loose sterile hyphae. In any case, the ascospores after they are dispersed, germinate under favourable conditions to produce a germ tube which develop into a hypha. When the hypha happens to encounter the appropriate algal partner, it establishes a symbiotic association and initiates a new lichen thallus formation. In case, the hypha fails to find its cognate partner, it degenerates.


7 - Biochemistry and secondary metabolites

There are two main groups of lichen compounds: primary metabolites (intracellular) and secondary metabolites (extracellular). Common intracellular products occurring in lichens include proteins, amino acids, polyols, carotenoids, polysaccharides, and vitamins, which are bound in the cell walls and the protoplasts, are often water-soluble, and can be extracted with boiling water (Fahselt 1994 b ). Some of these products are synthesized by the fungus and some by the alga. Since the lichen thallus is a composite structure, it is not always possible to decide where a particular compound is biosynthesized. Most of the intracellular products isolated from lichens are nonspecific, and also occur in free-living fungi, algae and in higher green plants (Hale 1983).The majority of organic compounds found in lichens are secondary metabolites of the fungal component, which are deposited on the surface of the hyphae rather than within the cells. These products are usually insoluble in water and can only be extracted with organic solvents. Carbon for the lichen is furnished primarily by the photosynthetic activity of the algal partner. Mosbach (1969) summarized the overall carbon metabolic sequence as involving photosynthesis in the photobiont followed by transport of the carbohydrate to the fungus, metabolism of the carbohydrate and subsequent biosynthesis of lichen secondary metabolites. The type of carbohydrate released by the alga and supplied to the fungus is determined by the photobiont, while in lichens containing cyanobacteria, the carbohydrate released and transferred to the fungus is glucose.


Lichens: Meaning, Characteristics and Classfication

In this article we will discuss about:- 1. Meaning of Lichens 2. Characteristics of Lichens 3. Habit and Habitat 4. Associated Members 5. Nature of Association 6. Classification 7. Structure of Thallus 8. Reproduction 9. Importance.

Meaning of Lichens:

Lichens are a small group of plants of composite nature, consisting of two dissimilar organisms, an alga-phycobiont (phycos — alga bios — life) and a fungus-mycobiont (mykes — fungus bios — life) living in a symbiotic asso­ciation.

Generally the fungal partner occupies the major portion of the thallus and produces its own reproductive structures. The algal partner manufactures the food through photosynthesis which probably diffuses out and is absorbed by the fungal partner.

Characteristics of Lichens:

1. Lichens are a group of plants of composite thalloid nature, formed by the association of algae and fungi.

2. The algal partner-produced carbohydrate through photosynthesis is utilised by both of them and the fungal partner serves the func­tion of absorption and retention of water.

3. Based on the morphological structure of thalli, they are of three types crustose, foliose and fruticose.

4. Lichen reproduces by all the three means – vegetative, asexual, and sexual.

(a) Vegetative reproduction: It takes place by fragmentation, decaying of older parts, by soredia and isidia.

(b) Asexual reproduction: By the formation of oidia.

(c) Sexual reproduction: By the formation of ascospores or basidiospores. Only fungal component is involved in sexual reproduction.

5. Ascospores are produced in Ascolichen.

(a) The male sex organ is flask-shaped spermogonium, produces unicellular spermatia.

(b) The female sex organ is carpogonium (ascogonium), differentiates into basal coiled oogonium and elongated tricho­gyne.

(c) The fruit body may be apothecia! (disc­shaped) or perithecial (flask-shaped) type.

(d) Asci develop inside the fruit body con­taining 8 ascospores. After liberating from the fruit body, the ascospores ger­minate and, in contact with suitable algae, they form new lichen.

6. Basidiospores are produced in Basidiolichen, generally look like bracket fungi and basidiospores are produced towards the lower side of the fruit body.

7. The growth of lichen is very slow, they can survive in adverse conditions with high temperature and dry condition.

Habit and Habitat of Lichens:

There is about 400 genera and 15,000 species of lichens, widely found in different regions of the world. The plant body is thalloid generally grows on bark of trees, leaves, dead logs, bare rocks etc., in different habitat. They grow luxuriantly in the forest areas with free or less pollution and with abundant moisture.

Some species like Cladonia rangiferina (reindeer moss) grows in the extremely cold con­dition of Arctic tundras and Antarctic regions. In India, they grow abundantly in Eastern Himalayan regions. They do not grow in the highly polluted regions like Industrial areas. The growth of lichen is very slow.

Depending on the growing region, the lichens are grouped as:

1. Corticoles:

Growing on bark of trees, mainly in the sub-tropical and tropical regions.

2. Saxicoles:

Growing on rocks, in cold climate.

3. Terricoles:

Growing on soil, in hot climate, with sufficient rain and dry summer.

Associated Members of Lichens:

The composite plant body of lichen consists of algal and fungal mem­bers.

The algal members belong to Chlorophyceae (Trebouxia, Trentepohlia, Coccomyxa etc.), Xanthophyceae (Heterococcus) and also Cyanobacteria (Nostoc, Scytonema etc.) (Fig. 4.111).

The fungal members mainly belong to Ascomycotina and a few to Basidiomycotina. Among the members of Ascomycotina, Disco­mycetes are very common producing huge apo­thecia, others belong to Pyrenomycetes or Loculoascomycetes.

The members of Basidiomycotina belong to Thelephoraceae.

Nature of Association of Lichens:

There are three views regarding the nature of association of algal and fungal partners in lichen:

1. According to some workers, the fungus lives parasitically, either partially or wholly, with the algal components.

This view gets sup­port for the following evidences:

(i) Presence of haustoria of fungus in algal cells of some lichen.

(ii) On separation, the alga of lichen is able to live independently, but the fungus cannot survive.

2. According to others, they live symbiotically, where both the partners are equally benefitted. The fungal member absorbs water and mineral from atmosphere and substratum, make available to the alga and also protects algal cells from adverse conditions like tem­perature etc. The algal member synthesises organic food sufficient for both of them.

3. According to another view, though the rela­tionship is symbiotic, the fungus shows pre­dominance over the algal partner, which simply lives as subordinate partner. It is like a master and slave relationship, termed helotism.

Classification of Lichens:

Natural system of classification is not avai­lable for lichens. They are classified on the nature and kinds of fruit bodies of the fungal partner.

Based on the structure of fruit bodies of fungal partners, Zahlbruckner (1926) classified lichens into two main groups:

1. Ascolichens:

The fungal member of this lichen belongs to Ascomycotina.

Based on the structure of the fruit body, they are divi­ded into two series:

(i) Gynocarpeae:

The fruit body is disc­shaped i.e., apothecial type. It is also known as Discolichen (e.g., Parmelia).

(ii) Pyrenocarpeae:

The fruit body is flask-shaped i.e., perithecial type. It is also known as Pyrenolichen (e.g., Dermatocarport).

2. Basidiolichen:

The fungal member of this lichen belongs to Basidiomycotina e.g., Dictyonema, Corella.

Later, Alexopoulos and Mims (1979) classi­fied lichens into three main groups:

i. Basidiolichen:

The fungal partner belongs to Basidiomycetes e.g., Dictyonema.

ii. Deuterolichen:

The fungal partner belongs to Deuteromycetes.

iii. Ascolichen:

The fungal partner belongs to Ascomycetes e.g., Parmelia, Cetraria.

Structure of Thallus in Lichens:

The plant body of lichen is thalloid with different shapes. They are usually grey or greyish green in colour, but some are red, yellow, orange or brown in colour.

A. External Structure of Thallus:

Based on the external morphology, general growth and nature of attachment, three main types or forms of lichens (crustose, foliose and fruticose) have been recog­nised. Later, based on detailed structures,

Hawksworth and Hill (1984) categorised the lichens into five main types or forms:

This is the simplest type, where the fungal mycelium envelops either single or small cluster of algal cells. The algal cell does not envelop all over by fungal hyphae. The lichen appears as powdery mass on the substratum, called leprose (Fig. 4.112A), e.g., Lepraria incana.

These are encrushing lichens where thallus is inconspicuous, flat and appears as a thin layer or crust on substra­tum like barks, stones, rocks etc. (Fig. 4.112B). They are either wholly or partially embedded in the substratum, e.g., Graphis, Lecanora, Ochrolechia, Strigula, Rhizocarpon, Verrucaria, Lecidia etc.

These are leaf-like lichens, where thallus is flat, horizontally spreading and with lobes. Some parts of the thallus are attached with the substratum by means of hyphal outgrowth, the rhizines, developed from the lower surface (Fig. 4.112C), e.g., Parmelia, Physcia, Peltigera, Anaptychia, Hypogymnia, Xanthoria, Gyrophora, Collema, Chauduria etc.

4. Fruticose (Frutex, Shrub):

These are shrubby lichens, where thalli are well developed, cylindrical branched, shrub-like (Fig. 4.112D), either grow erect (Cladonia) or hang from the substratum (Usnea). They are attached to the substratum by a basal disc e.g., Cladonla, Usnea, Letharia, Alectonia etc.

In this type, algal members are filamentous and well-developed. The algal filaments remain ensheathed or covered by only a few fungal hyphae. Here algal member remains as dominant partner, called filamen­tous type, e.g., Racodium, Ephebe, Cystocoleus etc.).

B. Internal Structure of Thallus:

Based on the distribution of algal member inside the thallus, the lichens are divided into two types. Homoisomerous or Homomerous and Heteromerous.

Here the fungal hyphae and the algal cells are more or less uniform­ly distributed throughout the thallus. The algal members belong to Cyanophyta. This type of orientation is found in crustose lichens. Both the partners intermingle and form thin outer protective layer (Fig. 4.11 3A), e.g., Leptogium, Collema etc.

Here the thallus is differen­tiated into four distinct layers upper cortex, algal zone, medulla, and lower cortex. The algal members are restricted in the algal zone only. This type of orientation is found in foliose and fruticose lichens (Fig. 4.113B) e.g., Physcia, Parmelia etc.

The detailed internal structure of this type is:

It is a thick, outermost protective covering, made up of com­pactly arranged interwoven fungal hyphae located at right angle to the surface of the fruit body. Usually there is no intercellular space between the hyphae, but if present, these are filled with gelatinous substances.

The algal zone occurs just below the upper cortex. The algal cells are entangled by the loosely interwoven fungal hyphae. The common algal mem­bers may belong to Cyanophyta like Gloeocapsa (unicellular) Nostoc, Rivularia (filamentous) etc. or to Chlorophyta like Chlorella, Cystococcus, Pleurococ­cus etc. This layer is either continuous or may break into patches and serve the function of photosynthesis.

The medulla is situated just below the algal zone, comprised of loosely interwoven thick-walled fungal hyphae with large space between them.

It is the lowermost layer of the thallus. This layer is composed of compactly arranged hyphae, which may arrange perpendicular or parallel to the surface of the thallus. Some of the hyphae in the lower surface may extend downwards and penetrate the sub­stratum which help in anchorage, known as rhizines.

The internal structure of Usnea, a fruticose lichen, shows different types of orientation. Being cylindrical in cross-section, the layers from out­side are cortex, medulla (composed of algal cell and fungal mycelium) and central chondroid axis (composed of compactly arranged fungal mycelia).

C. Specialised Structures of Thallus:

In some foliose lichen (e.g., Parmelia), the upper cortex is interrupted by some opening, called breathing pores, which help in gaseous exchange (Fig. 4.114A).

On the lower cortex of some foliose lichen (e.g., Sticta) small depressions develop, which appears as cup-like white spots, known as Cyphellae (Fig. 4.114B). Sometimes the pits that formed without any definite border are called Pseudocyphellae. Both the structures help in aeration.

These are small warty out­growths on the upper surface of the thallus (Fig. 4.114C). They contain fungal hyphae of the same type as the mother thallus, but the algal elements are always different. They probably help in retaining the moisture. In Neproma, the Cephalodia are endotrophic.

Reproduction in Lichens:

Lichen reproduces by all the three means, vegetative, asexual, and sexual.

I. Vegetative Reproduction:

It takes place by acci­dental injury where the thallus may be broken into fragments and each part is capable of growing normally into a thallus.

(b) By Death of Older Parts:

The older region of the basal part of the thallus dies, causing separation of some lobes or branches and each one grows normally into new thallus.

II. Asexual Reproduction:

1. Soredium (pi. Soredia):

These are small grayish white, bud-like outgrowths developed on the upper cortex of the thallus (Fig. 4.115A, B). They are com­posed of one.or few algal cells loosely enveloped by fungal hyphae. They are detached from the thallus by rain or wind and on germination they develop new thalli.

When soredia develop in an organised manner in a special pustule-like region, they are called Soralia (Fig. 4.115D), e.g., Parmelia Physcia etc.

These are small stalked simple or branched, grayish- black, coral-like outgrowths, developed on the upper surface of the thallus (Fig. 4.115C). The isidium has an outer corti­cal layer continuous with the upper cor­tex of the mother thallus which encloses the same algal and fungal elements as the mother.

They are of various shapes and may be coral-like in Peltigera, rod-like in Parmelia, cigar-like in Usnea, scale-like in Collema etc. It is generally constricted at the base and detached very easily from the parent thallus. Under favourable con­dition the isidium germinates and gives rise to a new thallus.

In addition to asexual reproduction, the isidia also take part in increasing the photo- synthetic area of the thallus.

Some lichen develops pycniospore or spermatium inside the flask-shaped pycnidium (Fig. 4.116A).

They usually behave as gametes, but in certain condition they germinate and develop fungal hyphae. These fungal hyphae, when in contact with the appropriate algal partner, develop into a new lichen thallus.

III. Sexual Reproduction:

Only fungal partner of the lichen reproduces sexually and forms fruit bodies on the thallus. The nature of sexual reproduction in ascolichen is like that of the members of Ascomycotina, whereas in Basidiolichen is like that of Basidio­mycotina members.

In Ascolichen, the female sex organ is the carpogonium and the male sex organ is called spermogonium (= pycnidium). The spermogo­nium (Fig. 4.116A) mostly develops close to carpogonium.

The carpogonium is multicellular and is differentiated into basal coiled ascogonium and upper elongated multicellular trichogyne (Fig. 4.116B). The ascogonium remains embedded in the algal zone, but the trichogyne projects out beyond the upper cortex.

The spermogonium is flask-shaped and develop spermatia from the inner layer (Fig. 4.116A). The spermatia behave as male gametes. The spermatium, after liberating from the spermo­gonium, gets attached with the trichogyne at the sticky projected part. On dissolution of the com­mon wall, the nucleus of spermatium migrates into the carpogonium and fuses with the egg.

Many ascogenous hyphae develop from the basal region of the fertilised ascogonium. The binucleate penultimate cell of the ascogenous hyphae develops into an ascus.

Both the nuclei of penultimate cell fuse and form diploid nucleus (2n), which undergoes first meiotic and then mitotic division — results in eight haploid daughter nuclei. Each haploid nucleus with some cytoplasm metamorphoses into an ascospore.

The asci remain intermingled with some sterile hyphae — the paraphyses. With further development, asci and paraphyses become surrounded by vegetative mycelium and form fruit body.

The fruit body may be ascohymenial type i.e., either apothecium (Fig. 4.117A) as in Parmelia and Anaptychia or perithecium as in Verrucaria and Darmatocarpon or ascolocular type (absence of true hymenium), which is also known as pseudothecia or ascostroma.

Internally, the cup-like (Fig. 4.117B, C) grooved region of a mature apothecium consists of three distinct parts the middle thecium (= hymenium), comprising of asci and paraphyses, is the fertile zone covered by two sterile zones — the upper epitheca and lower hypotheca. The region below the cup is differentiated like the vegetative thallus into outer cortex, algal zone and central medulla (Fig. 4.117B).

Usually the asci contain eight ascospores (Fig. 4.117C), but the number may be one in Lopadium, two in Endocarpon and even more than eight in Acarospora.

The ascospores may be unicellular or multicellular, uninucleate or multi­nucleate, and are of various shapes and sizes. After liberating from the ascus, the ascospore germinates in suitable medium and produces new hypha. The new hypha, after coming in con­tact with proper algal partner, develops into a new thallus.

In Basidiolichen (Fig. 4.118), the result of sexual reproduction is the formation of basi­diospores that developed on basidium as in typical basidiomycotina. The fungal member (belongs to Thelephoraceae) along with blue green alga, as algal partner forms the thalloid plant body.

The thallus grown over soil produces hypothallus without rhizines, but on tree trunk it grows like bracket fungi (Fig. 4.118A) and differ­entiates internally into upper cortex, algal layer, medulla and lower fertile region with basidium bearing basidiospores (Fig. 4.118B, C).

Importance of Lichens:

A. Economic Importance of Lichens:

The lichens are useful as well as harmful to mankind. The useful activities are much more than harmful ones. They are useful to mankind in various ways: as food and fodder, as medicine and industrial uses of various kinds.

Lichens are used as food by human being in many parts of the world and also by different animals like snail, catterpiliars, slugs, termites etc. They contain polysaccharide, lichenin cellulose, vitamin and certain enzymes.

Some uses of lichens are:

Some species of Parmelia are used as curry powder in India, Endocarpon miniatum is used as vege­table in Japan, Evernia prunastri for making bread in Egypt, and Cetraria islandica (Iceland moss) as food in Iceland. Others like species of Umbillicaria, Parmelia and Leanora are used as food in different parts of the world. In France, some of the lichens are used in the preparation of choco­lates and pastries.

Lichens like Lecanora saxicola and Aspicilia calcarea etc. are used as food by snails, caterpillars, termites, slugs etc.

Ramalina traxinea, R. fastigiata, Evernia prunastri, Lobaria pulmo- naria are used as fodder for animals, due to the presence of lichenin, a polysaccharide. Animals of Tundra region, especially reindeer and muskox use Cladonia rangifera (reindeer moss) as their common food. Dried lichens are fed to horses and other animals.

Lichens are medicinally important due to the presence of lichenin and some bitter or astringent substances. The lichens are being used as medicine since pre-Christian time. They have been used in the treatment of jaundice, diarrhoea, fevers, epilepsy, hydrophobia and skin diseases.

Cetraria islandica and Lobaria pulmonaria are used for tuberculosis and other lung diseases Parmelia sexatilisfor epilepsy Parmelia perlata for dyspepsia. Cladonia pyxidata for whooping cough Xanthoria parietina for jaundice and several species of Pertusaria, Cladonia and Cetraria islandica for the treatment of intermittent fever.

Usnic acid, a broad spectrum antibiotic obtained from species of Usnea and Cladonia, are used against various bacterial diseases. Usnea and Evernia furfuracea have been used as astringents in haemorrhages. Some lichens are used as important ingredients of many antiseptic creams, because of having spasmolytic and tumour-inhibiting proper­ties.

Lichens of various types are used in different kinds of industries.

Some lichens like Lobaria pulmonaria and Cetraria islandica are used in tanning leather.

(ii) Brewery and Distillation:

Lichens like Lobaria pulmonaria are used in brewing of beer. In Russia and Sweden, Usneaflorida, Cladonia rangiferina and Ramalina fraxinea are used in produc­tion of alcohol due to rich content of “lichenin”, a carbohydrate.

(iii) Preparation of Dye:

Dyes obtained from some lichens have been used since pre- Christian times for colouring fabrics etc.

Dyes may be of different colours like brown, red, purple, blue etc. The brown dye obtained from Parmelia omphalodes is used for dyeing of wool and silk fabrics. The red and purple dyes are available in Ochrolechia androgyna and O. tartaria.

The blue dye “Orchil”, obtained from Cetraria islandica and others, is used for dyeing woollen goods. Orcein, the active principal content of orchil-dye, is used extensively in laboratory during histological studies and for dyeing coir.

Litmus, an acid-base indicator dye, is extrac­ted from Roccella tinctoria, R. montagnei and also from Lasallia pustulata.

(iv) Cosmetics and Perfumery:

The aromatic compounds available in lichen thallus are extracted and used in the prepara­tion of cosmetic articles and perfumes. Essential oils extracted from species of Ramalina and Evernia are used in the manufacture of cosmetic soap.

Ramalina calicaris is used to whiten hair of wigs. Species of Usnea have the capacity of retaining scent and are commercially utilised in perfumery. Evernia prunastri and Pseudevernia furfuracea are used widely in perfumes.

Harmful Activities of Lichens:

1. Some lichens like Amphiloma and Cladonia parasitise on mosses and cause total destruc­tion of moss colonies.

2. Lichen like Usnea, with its holdfast hyphae, can penetrate deep into the cortex or deeper, and destroy the middle lamella and inner content of the cell causing total destruction.

3. Different lichens, mainly crustose type, cause serious damage to window glasses and marble stones of old buildings.

4. Lichens like Letharia vulpina (wolf moss) are highly poisonous. Vulpinic acid is the poisonous substance present in this lichen.

B. Ecological Importance of Lichens:

Lichens have some ecological importance.

Some of the activities in this respect are:

1. Pioneer of Rock Vegetation:

Lichens are pioneer colonisers on dry rocks. Due to their ability to grow with minimum nutrients and water, the crustose lichens colonise with luxuriant growth. The lichens secrete some acids which disintegrate the rocks.

After the death of the lichen, it mixes with the rock particles and forms thin layer of soil. The soil provides the plants like mosses to grow on it as the first successor, but, later, vascular plants begin to grow in the soil. In plant succession, Lecanora saxicola, a lichen, grows first then the moss Crtmmia pulvinata, after its death, forms a compact cushion on which Poa compressor grows later.

2. Accumulation of Radioactive Substance:

Lichens are efficient for absorption of diffe­rent substances. The Cladonia rangiferina, the ‘reindeer moss’, and Cetraria islandica, the ‘Iceland moss’ are the commonly avai­lable lichens in Tundra region. The fallout of radioactive strontium ( 90 Sr) and caesium ( 137 CS) from the atomic research centres are absorbed by lichen. Thus, lichen can purify the atmosphere from radioactive substances.

The lichens are eaten by caribou and rein­deer and pass on into the food-chain, especially to the Lapps and Eskimos. Thus, the radioactive substances are accumulated by the human beings.

3. Sensitivity to Air Pollutants:

Lichens are very much sensitive to air pollutants like SO2, CO, CO2 etc. thereby the number of lichen thalli in the polluted area is gradually reduced and, ultimately, comes down to nil. The crustose lichens can tolerate much more in polluted area than the other two types. For the above facts, the lichens are mar­kedly absent in cities and industrial areas. Thus, lichens are used as “pollution indica­tors”.


Lichens: Life History & Ecology

Lichens are formed from a combination of a fungal partner (mycobiont) and an algal partner (phycobiont). The fungal filaments surround and grow into the algal cells, and provide the majority of the lichen's physical bulk and shape. In the picture below at left of the lichen Physia, the fungal filaments have been stained blue, and the scattered algal cells red.

Also in the Physia section, you may notice a dark red layer along the top. This is an apothecium, much like the ones atop the British soldier lichen, below at right. An apothecium is a fungal reproductive structure, in which the fungus reproduces itself through the production of spores. These spores will disperse and germinate into new fungi, but they will not produce new lichens. For a lichen to reproduce, but the fungus and the alga must disperse together.

Lichens reproduce in two basic ways. Firstly, a lichen may produce soredia, or a cluster of algal cells wrapped in fungal filaments. These may disperse and form new lichens. A second way for the lichen to reproduce itself is through isidia, which are much like soredia except that isidia are enclosed within a layer of protective cortex tissue. An isidium is much more like a miniature lichen.

Lichens will grow almost anywhere that a stable and reasonbly well-lit surface occurs. This may include soil, rock, or even the sides of trees. A lichen may absorb certain mineral nutrients from any of these substrates on which it grows, but is generally self-reliant in feeding itself through photosynthesis in the algal cells. Thus, lichens growing on trees are not parasites on the trees and do not feed on them, any more than you feed on the chair you sit in. Lichens growing in trees are simply using the tree as a home. Lichens growing on rocks, though, may release chemicals which speed the degradation of the rock into soil, and thus promote production of new soils.

Most lichens are temperate or arctic, though there are many tropical and desert species. Lichens seem to do better in drier environments, where they are not often left in standing water. What the lichen considers dry, however, may not be what we would consider to be dry. In bayous and in cool rainforests, large lichens known as "old man's beard" may often be seen hanging from the branches of trees. Though there is considerable water in these habitats, the air is not saturated, and drying breezes may serve to dessicate arboreal organisms.

Lichens are most noticeable on the tundra, where lichens, mosses, and liverworts constitute the majority of ground cover. This cover helps to insulate the ground, and may provide forage for grazing animals. The so-called Reindeer "moss" is one such lichen.

Thus, lichens are hardy creatures able to survive in scorching deserts and frosty tundra. Their secrets of success are not well understood however. Two key features suggested as having important roles are (1) their ability to survive drying and (2) their complex chemistry.

Lichens may dry completely when moisture is unavailable. This is not simply dehydration as it occurs in plants and animals we are familiar with, but a complete loss of body water such that the lichen becomes quite brittle. When moisture is again available, they quickly absorb water, becoming soft and fleshy again. Not only can lichens undergo this drying, but while they are dry and brittle, pieces may flake off and later grow into new lichens.

The chemistry of lichens is rather complex but well-studied. Lichens manufacture a host of chemicals which presumably serve to reduce attacks by predators. Only a few insects feed on lichens -- some moths and beetles among them.

The most serious threat to the continued health of lichens is not predation, but the increased pollution of this century. Several studies have shown serious impacts on the growth and health of lichens resulting from factory and urban air pollution. Because some lichens are so sensitive, they are now being used to quickly and cheaply assess levels of air toxins in Europe and North America. Images of lichens on this page courtesy Tom Volk at the University of Wisconsin-La Crosse.


A Useful Dye and an Interesting Pigment

Litmus Paper

Litmus paper is very commonly used as an acid-base indicator, especially by students who need to know only the approximate pH of a substance. Litmus is a mixture of dyes extracted from specific lichens, especially Rosella tinctoria. Litmus paper is made from filter paper that has been treated with the dye. Neutral litmus paper is purple in color. It turns red when exposed to an acid and blue when exposed to a base (alkali).

Natural Sunscreens

Xanthoria parietina is a foliose lichen which contains a yellow pigment called parietin. This pigment absorbs ultraviolet radiation, acting as a sunscreen to protect the algal cells inside the lichen. Some other lichens contain sunscreens, too. It&aposs been suggested that the protective chemicals could be useful in human sunscreens.

Xanthoria parietina is a foliose lichen that has a high resistance to pollution, especially in the form of nitrogen the orange cup-like structures are apothecia and produce spores

Lichens reproduce in various ways. If the fungal component releases spores, as in the apothecium of Xanthoria parietina, the new fungus that is made won&apost form a lichen unless it meets the correct alga.

Usnea often hangs from branches and is sometimes known as old man&aposs beard. This is Usnea filipendula.


Classification (and lichenization & de-lichenization)

Humans have a penchant for classifying both living and non-living objects. Objects that are similar in some way can be grouped and given a name that allows them to be referred to as a group. An example of a group name is Homo sapiens and another example is Homo habilis. Technically these are examples of species names. The fact that both species names have Homo as the first element signifies that there is strong enough similarity between the members of the species Homo sapiens and those of the species Home habilis to warrant combining those two species into a larger group, a genus with the group name Homo. So far you have seen an example of individual organisms grouped together into a species and an example of species grouped into a genus. The process does not stop there since groups of similar genera are grouped into a family and, going to still broader groupings (or higher levels of classification), there are orders, classes, phyla and finally kingdoms. This process yields a hierarchical arrangement of groupings and such a hierarchy is an example of a classification scheme. This particular classification system is often referred to as the Linnean classification, though the use of some of the elements predates Linnaeus.

I have emphasized that there is some notion of similarity behind any classification scheme but I have not yet said how similarity is defined. That is a critical point which will be the subject of the next section. For the moment I will assume that there are definitions of similarity for lichens and plants and I will finish this section with some examples of classifications and a few more definitions. For the purpose of illustration here are classifications of the lichen Pannaria sphinctrina , Acacia pycnantha ( Australia's national flower, the Golden Wattle) and the grass Themeda triandra (Kangaroo Grass) .

'Species' is an example of a taxonomic rank while Pannaria sphinctrina, a particular species, is an example of a taxon. Moreover, it is a taxon at species rank. Genus, family, order, class, phylum and kingdom are also examples of taxonomic ranks. Lecanorales, Physciaceae, Fabales, Poaceae, Acacia and Themeda triandra are more examples of taxa, each being a taxon at some rank. In this hierarchical ordering of living organisms, the total number of species is greater than the number of genera, which in turn is greater than the number of families and so on. There are rules governing the creation of taxonomic names and one is that when a biologist proposes the creation of a new taxon at some taxonomic rank, he or she must ensure that there is at least one new taxon at each lower taxonomic rank. For example, a botanist who wishes to define a new order must ensure that within the new order there is at least one family, which in turn must contain at least one genus, which in turn must contain at least one species.

Warning: If you're looking for the full classification hierarchy for every lichen, this page is not for you. Nor will this page help you identify lichen specimens. Rather, the intent here is to give you some examples of the features or tools used in lichen identification and some general observations about lichen classification. Lichens are often referred to as lichenized fungi and it is the fungal partner on which the classification of a lichen is based. Therefore lichen classification is part of the subject of fungal classification. Moreover, since almost all lichens are lichenized ascomycetes the subject of lichen classification is almost totally part of the topic of ascomycete classification and you can find current thoughts about ascomycete classification on the Myconet website: http://www.fieldmuseum.org/myconet/. On that page click on current outline for the latest classification scheme, down to generic level. You'll find identification guides for Australian lichens listed on the FURTHER READING page.

Features used in lichen classification

At any given time, anyone attempting to classify lichens can use only those features that the available technology reveals. Several hundred years ago all that was available was the naked eye so features such as growth form, colour and substrate were used to differentiate lichens and by 1700 the concepts of genus and species were in use. Since the 1700s the development of tools or techniques such as optical microscopes, chemical testing, growth studies, electron microscopes and DNA analysis have revealed details about aspects such as lichen structure, physiology, metabolic products, ecology and genetics. Each new tool or method has provided information previously unobtainable. Sometimes this is simply an improvement in seeing something previously known. Early optical microscopes allowed the detection of spores, but with no fine detail of spore appearance, whereas today's optical microscopes reveal finer spore detail. Spores vary in shape, colour, size and septation depending on species. In other cases the new information is astounding and can generate considerable controversy. Until well into the 1800s lichens had been thought of as single organisms. With the help of the optical microscope Simon Schwendener was able to reveal the dual nature of lichens in a paper published in 1867, yet this idea was vehemently attacked by some influential lichenologists for some decades.

Whenever new information has become available it has inevitably supported some existing ideas of lichen classification but contradicted others. As long as new information is capable of being found lichen classification is based on unavoidably incomplete information and so classification schemes are 'works in progress'. A newly found contradiction simply means that some earlier concepts of taxon demarcation need to be re-examined since all the available evidence should be assessed. I have said that early classification was based on naked eye features. In the 19th century microscopic examination showed that some seemingly quite different species were very similar microscopically. Studies in the field showed there to be good evidence that at times the environment could influence thallus morphology, whereas microscopic features remained constant.

The example of STICTA AND 'DENDRISCOCAULON' shows also that thallus morphology could depend on whether the mycobiont was associated with an alga or a cyanobacterium. This meant that heavy reliance on macroscopic morphology as the basis for a classification scheme was untenable since no scientific classification should be based on features that were not fixed, but could vary depending on where a thallus grew or which photobiont occurred in the thallus. By the end of the 19th century increased weight was given to microscopic features in the definition of taxa, though macroscopic morphology was not ignored. One result of this work was that some species, once thought to be distinct, were shown to be identical. Such groups of species were lumped into one. Conversely, there were also cases where what had been thought to be one species, based on naked eye features, could be divided into two (or perhaps more) based on the evidence of the optical microscope. Thus, what had been one species was split into two or more. The advent of electron microscopes in the 20th century allowed the study of very fine morphological detail and cellular structure. In particular the structure of apothecia, perithecia and asci became important in classification of the ascomycetes in general. Some of those features had been used in ascomycete classification since the late 1800s but electron microscope studies gave more detailed structural information. Non-structural features have also been used and have also led to the lumping or splitting of species. LICHEN CHEMISTRY has been accepted as important for the identification of lichens from the late 1800s and has been used as a taxonomic tool for over a century, though there has been much heated debate as to the connection between CHEMISTRY AND TAXONOMY. The study of how thalli grow and develop their various features is another way of discerning similarities and differences and so have played an important role in classification schemes.

Modern evolutionary theory developed from the later 1800s onward. Evolution results in change to organismal traits over many generations, leading to diversity in the descendants many generations hence. The division of organisms into species, genera and so on has always been a way of summarizing that diversity. The concept of evolution therefore provides a biological basis for a natural classification and it has become a goal to base the classification of living organisms on the evolutionary relationships between them. Ideally, to develop such a classification, the evolutionary history of lichens would be revealed by the study of numerous fossils of many ages which showed when various structural features appeared. Unfortunately the number of lichen fossils is not very large and there are few very old fossils. Hence, evolutionary relationships need to be determined, somehow, from what is found in lichens alive today. In the latter part of the 20th century there were various hypotheses as to how features such as micro-morphology, chemistry and thallus development indicated the degree of evolutionary closeness between species and such hypotheses were incorporated into classification schemes.

More recently there has been much emphasis on analysis of genomes. An organism's genome is its hereditary information, stored as DNA. Given that DNA is inherited, albeit mixed from both parents and with changes over time, makes genomic analyses attractive as a means of determining genetic and hence evolutionary closeness. In such analyses one looks at equivalent sections from the genomes of different species and the results are presented as sequences of letters, indicating how the four basic DNA components (adenine, cytosine, guanine, thymine) are arranged. If you have the DNA sequences from different species you can align them and then look for the number of differences between sequences. For example, suppose that the following are corresponding sections from the sequences of three species:

sequence 1: . AG G TCA T ATT A CCGAACTTA.

sequence 2: . AG T T C A C ATT C CCGAACT T A.

sequence 3: . AGTT G ACATTCCCGAACT G A.

In these parts the three sequences are very similar, with the three differences between sequence 1 and sequence 2 shown in red , and the two differences between sequence 2 and sequence 3 shown in blue . Essentially, counting the number of places in which sequences differ gives the basis for a numerical measure of closeness. You could say that, with regard to this section of DNA, species 1 is closer to species 2 than it is to species 3 since it takes three changes to transform sequence 1 into sequence 2, but five changes to transform it into sequence 3. This simplistic scenario is sufficient to explain the basic idea but in reality there may be many complications, fortunately irrelevant for the purpose of this page, in deriving measures of closeness between the three sequences.

All analysis (whether of growth form, spores, asci, secondary metabolites or genomes) is carried out on individual thalli. Various groupings of characteristics are used to define species, genera and so on, with fewer characteristics as you go up in taxonomic rank. Once you know the characteristics that define different species you can use the differences in the characteristics to derive some measure of similarity or, in an evolutionary classification, degree of evolutionary closeness.

Tree diagrams

Once you have determined the degrees of closeness between different species you can display this information in a diagram such as the one alongside this paragraph, similar to a human family tree. The dotted line indicates that there are more species involved in the analysis, but we are interested in only the 11 shown here and indicated by letters.In this tree the blue dots, called nodes, are like ancestors in a family tree.

Since the classification that led to this tree is based on evolutionary principles and evolution involves changes between ancestors and descendents node 4 indicates a species ancestral to Q and O. Nodes 1, 2 and 3 are also ancestral to Q and O but 4 is the most recent common ancestor of Q and O while 3 indicates the most recent common ancestor of Q and D (and also of O and D). This diagram is saying that 3 marks the beginning of the divergence between the lineage that gave rise to D and the lineage that gave rise to the pair Q and O, while 4 marks a further point of divergence. Of the eleven species three have a trait called RED. This trait arose at some point and a diagram such as the one here can suggest hypotheses as to when that happened. One possibility is that 1, the most recent common ancestor of all eleven species had the trait RED. In that case the trait was lost by 2 (or some descendents of 2), by G and by U - in other words the trait was lost at least three times. If 1 had not been RED, then we could explain the current distribution of RED by positing a gain of RED by 6 and a loss by U - just two changes. This is a more economical hypothesis than the first one, but by no means proof that this in fact happened. As we are unable to analyse the ancestral species all we can say is that the current situation can be explained with a minimum of two changes in trait.

A tree such as this shows the species' evolutionary relationships, or phylogeny, but a phylogenetic tree is not itself a classification, though it can suggest possible classifications. In this example you might argue that there are three obvious genera here, namely the groups (QOD), (BPR) and (CUJSG). Someone else may argue that rather than three genera there should be just two, with the first two of the above three groups defined as the one genus. Each of those ideas is justified by the evidence presented by the diagram. A monophyletic group is defined as one consisting of an ancestor and all its descendants. Hence the group (3,4,Q,O,D), of which only the last three are extant today, is an example of a monophyletic group. If a classification is to be consistent with phylogeny then only taxa consistent with monophyly would be accepted. Hence (D,O,Q) would be an acceptable genus, as would be the other suggestions for genera just given. At an earlier level of knowledge the trait of RED may have been thought a significant feature and hence used to help define a genus consisting just of C, J and S. Current knowledge, as presented by the diagram, shows that RED is not a significant indicator of evolutionary closeness since C is closer to the non-RED U than to the other RED species. On the basis of the evidence presented by the diagram (C,J,S) is not monophyletic since the most recent common ancestor, 6, also has U as a descendant. The group (C,J,S) is paraphyletic - meaning that it does not include all descendents of the group's most recent common ancestor.

Despite the desirability of a monophyletic basis, paraphyletic groups are still widely used in lichen taxonomy. One factor is that much is still unknown. For example, if you wish to draw sound conclusions from genomic evidence it is important to study both the genomes of a large number of species and also different parts of each genome. Currently there are still many species for which little or no genomic information is available. Another point is that tree diagrams, which are very common in the lichenological literature, can look impressive but often there is some uncertainty in the evidence on which a tree is based or the one set of evidence is capable of generating two or more different trees. Trees that appear in publications typically have little numbers on the various branches. The production of trees is essentially a statistical process and the numbers are a measure of the unavoidable statistical uncertainty. You can look at those numbers as indicators of how well you could trust different parts of the tree and where more investigation is needed. Given facts such as these it is often a very sensible policy to keep using 'unsuitable' genera, until there is strong evidence in favour of a different classification. Moreover, there are different degrees of 'unsuitable' genera. In the artificial example given here, earlier evidence suggested that group C, J and S were closely related and the current evidence still supports a close relationship between the three so there is not a major change in the status of these three. The circumstances would be different if, for example, Q, B and C previously had been held to constitute a genus.

Now, a lichen tree

If lichenization had evolved just once and, once gained, had never been lost by descendents, all current lichens would form a monophyletic group and could then be treated as a self-contained group of organisms. Lichens do not form a monophyletic group. For a start, there are both ascomycete and basidiomycete lichenized fungi, albeit very few of the latter. Perhaps lichenization arose twice, once in the basidiomycetes, once in the ascomycetes and gave rise to two monophyletic groups - one of basidiolichens and one of ascolichens. The basidiolichens do not constitute a monophyletic group and neither do the ascolichens. The following figure shows where the lichenized ascomycetes fit into the ascomycetes as a whole and is based on genomic research published in 2009.

The figure is in two parts. The large tree on the left shows the classes that contain lichenized fungi with one class, Eurotiomycetes, given in more detail, the orders within that class being shown and three of them named. If a taxon consists only of lichenized fungi then it is shown as a red line. A taxon containing only non-lichenized fungi is shown by a blue line and taxa in which both lichenized and non-lichenized fungi are found are shown in red and blue. The lines for the latter are drawn thicker, simply to show the bicolouring more easily and the line thickness has no other significance. The class Lecanoromycetes consists almost totally of lichenized fungi but there is a small number of non-lichenized species within the class, hence the blue dot within the Lecanoromyctes. This class contains the majority of the lichenized fungi (containing about 14,000 of the approximately 18,000 known lichen species). The Dothideomycetes is the largest class within the ascomycetes and contains about 19,000 species - but only a small number of lichenized species. The Verrucariales and Pyrenulales consist mostly of lichenized fungi. The yellow area in the small tree to the right shows where the large tree fits into the tree of all ascomycetes. As you can see there are three other groups of ascomycetes, all non-lichenized, and they have been labelled X, Y and Z. The first of those groups contains about 18,000 species while Y and Z, combined, contain about 3,000.

At the extreme left of the large tree is the most recent common ancestor of all the taxa in that tree. Either that ancestor was capable of forming a lichenized association or it wasn't. In either case the current distribution of lichenized and non-lichenized taxa calls for one or more losses or gains of lichenization to account for the current mix of lichenized and non-lichenized taxa. Here are some of the hypotheses supported by the evidence behind the above tree.

There was a single lichenization in the immediate ancestor of the Lecanoromyctes and at least one loss of lichenization within that class. The immediate ancestors of each of the Lichinomycetes, Candelariales and Arthoniomycetes was lichenized. The Dothideomycetes is the one class within which lichenization has occurred several times independently but the evidence is insufficient to determine whether the immediate ancestor of the Dothideomycetes was lichenized or not - hence the question mark. With regard to the group consisting of the Chaetothyriales, Verrucariales and Pyrenulales the evidence is unclear. It does not distinguish between the hypothesis of two gains of lichenization (early in each of the Verrucariales and Pyrenulales) from a non-lichenized common ancestor and the hypothesis of a gain of lichenization by a common ancestor of the Verrucariales and the Pyrenulales, followed by a loss of lichenization in the Chaetothyriales. Regardless of that, the evidence supports the hypothesis that there has been at least one loss of lichenization within each of the Verrucariales and the Pyrenulales.

As more taxa and larger sections of genomes are studied some conclusions may change. This is shown already by the fact that the more extensive investigation behind the 2009 publication did not support an earlier hypothesis, published in 2001, that lichenization was the ancestral state for the majority of current ascomycete taxa. However, while there are differences between the conclusions of 2001 and 2009, both studies supported the hypothesis that lichenization had been gained and lost several times.

Apart and together

Lichens are classified by the fungal partner, so all lichens belong to the fungal kingdom. Though this fungal-based taxonomy of lichens has been accepted for over a century, for much of that time lichenized and non-lichenized fungi have been studied largely as separate subjects. As one lichenologist wrote in 1973:

Even a superficial analysis of any of the past systems will show that we cannot really speak of a true integration of lichenized fungi in any presently accepted fungal system. Lichen systematists have hardly ever been really familiar with the corresponding fungal groups, and mycologists have had enough difficulties with their own groups without bringing in the lichenized fungi.

Twenty-one years earlier another lichenologist had written:

Whereas in the last half-century the classification of Ascomycetes - the fungal class of overwhelming importance in the present study - has been completely reformed, the lichen system presented by Zahlbruckner in 1903-07 is still accepted and used by most lichenologists. This is due not so much to any excellence inherent in it as to the lack of interest manifested by most lichenologists vis-à-vis taxa above species level, and to their lack of knowledge of the general taxonomy of fungi.

The person referred to was Alexander Zahlbruckner (1860-1938), an Austrian lichenologist, and in relation to Zahlbruckner's classification the same author noted that ". it has become dominating in a way strongly detrimental to the development of a more natural lichen classification".

It would be natural to ask how the situation described by these quotations could be tolerated for so long. Has it not been harmful to a proper classification of the lichenized fungi - and also of the non-lichenized fungi? It is worth repeating some numbers given earlier. About 64,000 ascomycete species are known, of which about 18,000 are lichenized. The Lecanoromycetes account for about 14,000 of the known lichenized ascomycetes and the second largest lichenized class, the Arthoniomycetes, for about 1,500. A very large proportion of lichens belong to just one class and, on current evidence, that class arose from one gain of lichenization. It is therefore possible to do much work on lichen classification by working entirely within that class, in isolation from the remaining ascomcyetes. Certainly if you are interested in the origins of that class, you need to think of ascomycetes as a whole, but once you are studying the species within that class the rest of the ascomycetes are largely irrelevant. The species within the Arthoniales form a similar self-contained group. This is not a denial of the need to look at fungi as a whole. Instead, the small number of gains or losses of lichenization has meant that it has been possible to study large groups of ascomcyetes more or less in isolation from each other. The situation would have been quite different if the lichenized fungi were spread widely through the fungal kingdom. This would have produced many additional cases like the Pyrenulales and the Verrucariales, with more intermingling of lichenized and non-lichenized fungi. In such a situation a non-integrated approach would have been worthless from the beginning. Another fact is that over the past twenty years there has been much new evidence relevant to fungal phylogeny as a whole, considerable changes in classificatory ideas and during those twenty years there has been integration of lichenized and non-lichenized fungi.

The period before then was not wasted. There was enough productive work to do in accumulating the essential species information that has allowed the better understanding of fungal (and hence also lichen) phylogeny in recent times.


Reindeer lichens are having more sex than expected

In northern Canada, the forest floor is carpeted with reindeer lichens. They look like a moss made of tiny gray branches, but they're stranger than that: they're composite organisms, a fungus and algae living together as one. They're a major part of reindeer diets, hence the name, and the forest depends on them to move nutrients through the ecosystem. They also, at least in parts of Quebec, are having a lot more sex than scientists expected. In a new study in the American Journal of Botany, researchers found that the reindeer lichens they examined have unexpected levels of genetic diversity, indicating that the lichens have been doing more gene-mixing with each other than the scientists would have guessed.

"We were surprised because this species of reindeer lichen had always been considered mainly a clonal species that reproduces asexually," says Marta Alonso-García, the paper's lead author and a postdoctoral fellow at Quebec's Université-Laval. "It doesn't follow the expected pattern."

Reindeer lichens swing both ways: they can reproduce sexually via spores, or they can asexually clone themselves. When fungi reproduce sexually, they send out root-like structures toward a neighboring fungus and exchange genetic information when they touch. They then release spores, single cells containing genetic material, which travel on the wind and disperse. When they land, they start growing and produce a new baby fungus that's genetically distinct from its parents. In asexual clonal reproduction, on the other hand, a piece of the entire lichen (fungus and alga), called the thallus, is pinched off and regrows into a whole organism that's genetically identical to its parent.

The two reproductive methods have different advantages. "Sexual reproduction is very costly," says Felix Grewe, the co-director of the Field Museum's Grainger Bioinformatics Center and a co-author of the study. "You have to find your partner, it's more difficult than reproducing asexually. But many organisms do it because when you have this combining and mixing of genetic traits, it enables you to weed out negative mutations long-term among other benefits."

The researchers were examining reindeer lichens (Cladonia stellaris) to learn about their genetic patterns. "We used DNA sequences to tease apart the genetic relationships between populations of this lichen," says Alonso-García. "We tested whether individuals from northern Quebec (Hudson Bay) were genetically different from those from the South (Parc National des Grands-Jardins, two hours from Québec City). At the same time, due to its important role in the colonization process after a fire, we evaluated lichen genetic diversity along a post-fire succession."

Lichens can reveal a lot about how wildfires affect ecosystems. "Wildfire is the most significant disturbance in the world's northernmost forests, and it plays a major role in determining the distribution and composition of plant communities," says Alonso-García. "In Eastern North America, four successional vegetation stages are generally identified after a fire. During the first stage, crustose lichens and mosses colonize the burned surface. Subsequently, the soil is covered by cup and horn lichens. The landscape remains mostly uniform for around 20 years until the arrival of fruticose lichens which replace the previous vegetation. Cladonia stellaris arrives the last one, usually three or four decades after fire." By studying genetic variations in reindeer lichens, the researchers hoped to learn how lichens recolonize an area after a fire.

To study the lichens' DNA, the researchers ground up samples of lichens and extracted their DNA. But lichens present an extra challenge in this process, since they're made up of a fungus and an alga (or a kind of bacteria that performs photosynthesis) living together. "That means that all the DNA is mixed up together, we get one pool that contains fungal DNA and algal DNA," says Grewe. "We have to carefully filter and sort the sequence reads bioinformatically." The main body of a lichen is made up of the fungus, so the researchers wanted to focus on the fungal component's DNA. By comparing the pool of DNA to existing genomes, the researchers were able to pick out the DNA belonging to the fungus, and they could then compare the fungal DNA from reindeer lichens from different areas of Quebec.

What they found was surprising: in general, there was a lot more genetic variation in the lichens than the researchers expected, and that indicates hanky-panky. "It's a general assumption was that these reindeer lichens mainly reproduce asexually because there's little evidence for them producing spores, but now the genetic data shows all this diversity, and that leads to the assumption that might be some form of sex," says Grewe.

"We were expecting that lichens from North Quebec would be more similar to each other than to those from Parc National des Grands-Jardins. However, our results suggest constant migration of C. stellaris between populations throughout Eastern North America," says Alonso-García. "In fact, contrary to the widespread belief, we found many reproductive structures in the species and these structures are formed after sexual reproduction."

But while the lichens are apparently doing more genetic intermingling than expected, the researchers also found that after a forest fire, the new lichens that crop up are genetically similar to the ones that were there before. That was counterintuitive -- the thought had been that the little cloned lichen bits would be destroyed in a fire, and that the repopulation of lichens would be growing from spores that arrived on the wind from other areas. "Regarding the genetic diversity of the species after fires, we found no differences along four stages of the succession. This was also astonishing because time since the last fire increases the probability that clonal fragments successfully reached the sites, enhancing genetic diversity," says Alonso-García.

In addition to revealing the hidden sex lives of reindeer lichen, the study could have implications for forest conservation. "We have learned that time since the last fire does not necessarily mean more genetic diversity, so conservation strategies in boreal forests should take this into account," says Alonso-García. "Prioritizing the protection of an area should not be based exclusively on its age. This is quite important because funding is usually limited, so we cannot carry out conservation activities in the entire forest." In short: if conservation scientists want to protect areas of forest with genetically diverse lichen populations, the forest's age isn't the only indicator of diversity.

Grewe adds the importance of bioinformatics in learning about how organisms are related to each other. "It is astonishing that today we can have such a detailed view of the evolution of populations using bioinformatics," says Grewe. "This is another good example of how advancement in sequencing technology allows us to learn about the evolution of an organism in more detail than ever before."


Treatment

When lichen sclerosus affects the skin in parts of the body other than the genitals, it rarely needs to be treated. The symptoms tend to be very mild and will usually disappear with time.

However, lichen sclerosus of the genital skin should be treated, even when it doesn't cause itching or pain, to prevent the scarring that can interfere with urination or sexual intercourse or both. The disease has also been linked to certain cancers. It doesn't cause cancer, but skin that is scarred by lichen sclerosus is more likely to develop cancer. About 1 in 20 women with untreated vulvar lichen sclerosus develops skin cancer. It's important to get proper treatment and to see your doctor every 6 to 12 months to monitor and treat any changes that might signal skin cancer.  

Topical corticosteroids are usually the first line of defense against lichen sclerosus to both cure the disease and to restore the skin's normal texture and strength. However, steroids won't reverse any scarring that may have already occurred. And because they're very strong, it's important to check back with a doctor frequently to check the skin for side effects when the medication is used every day.

Once symptoms are gone and skin has regained its strength, the medication can be used less frequently, but may still be needed a few times a week to keep lichen sclerosus in remission.

If the disease doesn't clear up after a few months of using a topical steroid cream or ointment, a doctor may move on to prescribing a medication that modulates the immune system, such as Protopic (tacrolimus) or Elidel (pimecrolimus). And for people who can't tolerate other medications, retinoids may be helpful. Sometimes, too, other factors, such as low estrogen levels that cause vaginal dryness and soreness, a skin infection, or irritation or allergy to the medication, can keep symptoms from clearing up.

For men whose lichen sclerosus won't clear up with medication, circumcision almost always is effective.   Once the foreskin is removed, the disease usually does not recur. This isn't the case for women, though, and so surgery in the genital area or around the anus generally isn't recommended. But most of the time medication will do the job of getting rid of lichen sclerosus once and for all.


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