Geography 316:  Biogeography     In progress  02/01/2006

The Biogeography of  the Lungwort (Lobaria pulmonaria)
 

by Catherine Daniels, student in Geography 316  Fall 2003

Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.  All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

Species Name:  Lobaria pulmonaria

Kingdom         Fungi

Phylum            Ascomycota

Class               Ascomycetes

Order              Peltigerales

Family             Lobariaceae

Genus             Lobaria

Species           Lobaria pulmonaria

         Taxonomic Classification for lichens is specialized in that lichens consist of two separate organisms a mycobiont (fungus) and a photobiont (alga).  For taxonomic purposes, the name given to the lichen refers to the fungal partner because every lichen has a unique fungus.  In contrast, green algae and cyanobacteria (the photobiont partner) do not come to bear on the taxonomic classification of lichens because they occur in association with many different fungi.  The type of green algae associated with Lobaria pulmonaria is Dictyochloropsis. 

 

Description of Species

 

 

        Lobaria pulmonaria, commonly known as tree lungwort, is a folios lichen, one of many morphological classifications that describe lichens that are leafy looking, lobed, relatively circular in shape and have a distinct upper and lower surface (Doell & Doell, 2000).  L. pulmonaria is characterized by a more or less flattened thallus, a term that refers to the body of the lichen, encompassing both the algal and fungal components.  Lobaria pulmonaria is distinguished by its leaf like lobes, and a distinct strongly ridged and pitted upper and lower surface.  It is bright green when wet and brown to olive-brown when dry (Doell & Doell, 2000).  This species of lichen often forms a layer of fine hair or fuzz on its lower surface, called tomentum, usually the result of  a superficial growth of colorless hyphae or fungal threads (Brodo, et al., 2001.) 

Source: Lichens of North America.  2001. Brodo et al.  

 

 Natural History

        Lichens are utterly unique.  What we may see as inconsequential splashes of green, orange and red on rocks at the sides of hiking paths, or as black and brown goo at the tidal fringes, is described most intriguingly in the following quote by Tehler (1996), “Lichens are not organisms. Lichens are small ecosystems.” 

Perhaps lichens can best be described as dual- or composite-organisms, in that they are an association of two completely different organisms: a fungus (mycobiont) that exists in association with a photosynthetic partner (photobiont), usually algae and sometimes cyanobacteria.  This symbiotic relationship is beneficial for both partners in that the algae provide food for the fungi in the form of carbohydrates produced through photosynthesis, while the fungi provide structure, moisture, and protection for the algae.  There are some, however, who consider the lichen association to be one of controlled parasitism, and not a symbiotic relationship at all.  They would argue that the fungi seem to benefit more from the relationship than do the algae.  In fact, James Crombie, a prominent 19th Century lichenologist thought of the lichen association as “. . . the unnatural union between a captive algal damsel and tyrant fungal master (Crombie in Purvis 2000).”

Regardless of the nature of the relationship, it is this very relationship that allows each to colonize environments that neither would be able to colonize alone.  And lichens have been remarkably successful.  Vegetation dominated by lichens covers around 8% of the earth’s land surface (Purvis, 2000).  Today over 14,000 species of lichen exist in every conceivable habitat including both poles, the tropics, deserts, inter-tidal zones, high mountain peaks, and the arctic tundra where lichen is the dominant vegetation.  The only habitat in which lichens do not exist is the deep sea.  Lichens are remarkably adaptable and will attach to almost every kind of surface or substrate including soil, rocks, tree bark, moss, plaster, metal, insect bodies and even tortoise shells.

Reproduction

            Lichens reproduce by both sexual and asexual means.  Sexual reproduction is less common, with success dependent on the chance encounter of fungus and alga in order for the fungus to become lichenized.   The chances of reproductive success are increased with asexual reproduction in which the fungus and alga are already united and the only variable for success is correct environmental conditions.  Both methods of reproduction are described below for lichens in general and then specifically for L. pulmonaria.

            Sexual Reproduction:  Is reproduction that occurs through the production of sexual fruiting bodies (apothecia) that contain spore sacs (asci).  These fruiting bodies are normally perennial, occur throughout the year and may be as long-lived as 50-years.  Spores are discharged and after they germinate they must encounter a compatible alga in order to form new lichen.  Some lichens have solved this seemingly insurmountable dilemma by carrying algal cells in their fruiting bodies that are released along with the fungal spores.  This mechanism of reproduction, however, is rare among lichens.  How exactly sexual reproduction happens in lichens has never been observed, so it is not entirely understood (Brodo et al., 2001.)

            Asexual (Vegetative) Reproduction:  Lichens increase their chances of reproductive success by producing asexually through the use of propagules.  Lichens produce two types of propagules:  Soredia, which consist of clusters of photobiont cells enveloped by fungal hyphae, and isidia, which consist of smooth peg like outgrowths that contain photobiont cells.  Both soredia and isidia are dispersed by wind, water and small animals, and transported to new locations, where, if conditions are favorable, they will grow into new lichens.

            Lobaria pulmonaria reproduce asexually through the mechanism of propagules.   L. pulmonaria employ both types of propagules, the soredium and isidium (Brodo et al., 2001).  To expand on the description above and elucidate the process that is specific to L. pulmonaria, soredia, as described previously, are reproductive bodies consisting of tiny balls of hyphae (fungal threads) enveloping a few clusters of photosynthetic cells, which in the case of L pulmonaria, are released through breaks in the thallus cortex, the outer protective layers of the lichen thallus, often composed entirely of fungal hyphae with thick, gelatinized walls.  Soredia tend to develop on the lobe margins and along the thallus ridges.  Isidia are reproductive bodies consisting of minute, easily detached, peg like thalli outgrowths which, like soredia, contain both fungal hypae and photosynthetic cells, and are often found emerging among the soredia.

Evolution:

            Many consider the lichen to be among the first living things to have emerged from the primordial soup (Purvis, 2000).  The thinking is that lichenized fungi were able to exploit new ecological niches and contribute to soil formation (Brady & Weil, 2002; Purvis, 2000.)  Thus, it is thought that lichens played an essential role in making the terrestrial realm more hospitable to other organisms. 

            The lichen lifestyle is widespread among many different fungal groups and it has been documented through DNA sequencing that the relationship is phylophyletic, derived from two or more ancestral lines (Tehler 1996.)  In the order Ascomycetes, of which Lobaria pulmonaria is a member, and which contains 98% of known lichenized fungi, at least four independent origins have been documented (Lutzoni, Pagel & Reeb, 2001.)  In Ascomycetes, lichen formation is the dominant lifestyle, with nearly half the species in this order associating with algae (Gargus, et al, 1995.)  The oldest undisputed fossil lichen is from the Lower Devonian, 400 million years ago, found in the Rynie chert formation in Scotland (Purvis, 2000). 

            It is only since 1869, when it was discovered that lichens were composed of two separate organisms, that scientists have understood the true nature of lichen.   And only since 1959 that scientific names of lichens have been restricted to their fungal partners (Hawksworth, 2005), paving the path to conceptualizing lichens more as a fungal lifestyle than as a separate species of fungi.  It is only since 1995 that we have molecular data about the evolutionary origins of the lichen lifestyle (Barinaga, 1995.) 

            Because lichens are a composite organism they are not considered a systematic unit, and thus must be broken down into their component units in order to understand their evolution.  In the case of lichens, it is the fungal partner alone that is used to understand its evolutionary path.  The use of cladistics, although widely accepted in many fields of systematics, has not, according to Tehler (1996), been accepted widely by lichenologists, who have been slow in adopting cladistic methods for constructing phylogenies.  Today scientists have produced proposed evolutionary paths to the sub-order level but these are still being debated within the field (Nash, 1996) and consensus has yet to be reached.   In addition, because phylogenies are based on probabilities, relationships certainly will change over time as more is learned about the lichen relationship (Barinaga, 1995.)

Distribution:

 

           Lobaria pulmonaria is widely distributed, occurring in Africa, Asia, Europe, and North America. It is the most widely distributed and common Lobaria in North America, typically found from Alaska south to central California and from the Great Lakes region and Appalachia north to Newfoundland (Brodo et al. 2001.)  The typical habitat for this species is on trees, mossy rocks, and wood in mature forests, usually in the shade.  In California, Lobaria pulmonaria is typically associated with oaks and other broadleaf trees in northern coastal and montane forests. 

Lobaria pulmonaria are often associated with pristine, ancient forests that have never been completely felled (Purvis, 2000.)  Because of this association, the species is used as an indicator of old growth forests (Purvis, 2000).  As such, the presence or absence of Lobaria pulmonaria helps to guide conservation efforts in forests in which it is typically found.

 
Source: Lichens of North America.  2001.  Brodo et al.  

Other interesting issues:

The anthropogenic uses of Lobaria pulmonaria can be described by invoking the Doctrine of Signatures, which was a classification method employed by the herbalists of the Renaissance, and accepted until the latter part of the 19th century (Purvis, 2000.)  The doctrine of Signatures held that everything on earth was put there for the use of human beings, with the specific use of a plant indicated by its physical form.  Lobaria pulmonaria or Lungwort, as its name implies, resembles the lobes of a lung, and was commonly used for treating respiratory disorders. 

            Outside of the uses described in the Doctrine of Signatures, Lobaria pulmonaria has long been used as a source of boiling water dyes.  In India it has been used to treat hemorrhages and eczema (Sharnoff, Sharnoff & Brodo, 2001.)  It was also used by Siberian monks in the seventeenth and eighteenth centuries as a bitter flavoring for beer (Brodo et al. 2001.)

Bibliography
 

Barinaga, Marcia.  1995.  Origins of Lichen Fungi Explored.  Science.  Vol. 268, No. 5216, p. 1437.

Brady, Nyle C. and Ray R. Weil.  2002.  The Nature and Properties of Soils, 13th ed.  Prentice Hall: New Jersey.  909 pp.

Brodo, Irwin M., Sylvia Duran Sharnoff, and Stephen Sharnoff.  2001.  Lichens of North America.  Yale University Press: New Haven and London.  769 pp.

Doell, Janet and Richard Doell.  2000.  A Mini Guide to Some Common California Lichens.  California Lichen Society: 89 pp.

Gargus, Andrea, Paula T. DePriest, Martin Grube, Anders Tehler. 1995. Multiple Origins of Lichen Symbiosis in Fungi Suggested by SSU rDNA Phylogeny.  Science. Vol. 268, No. 5216, pp. 1492-1495.

Hawksworth, David.  2005.  To be or not to be a lichen.  Nature. Vol. 433, pg. 468.

Lutzoni, Francois, Mark Pagel, Valerie Reeb.  2001.  Major Fungal Lineages Are Derived from Lichen Symbiotic Ancestors.  Nature.  Vol. 411, No. 6840, p 937.

Purvis, William.  2000.  Lichens.  Smithsonian Institution Press: Washington D.C. 112pp.

Tehler, A.  1996.  Systematics, Phylogeny, and Classification.  In Lichen Biology, Ed. Thomas H. Nash III.  Cambridge University Press: Cambridge.  254pp.

  send comments to bholzman@sfsu.edu
 

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