MAP LICHEN: It’s ALIVE! Like many a geologist before him,…

MAP LICHEN: It’s ALIVE! Like many a geologist before him,…

MAP LICHEN: It’s ALIVE!

Like many a geologist before him, this lizard sits atop a rock surface totally obscured by the growth of lichen. Though we usually find lichen to be an annoyance that a rock hammer can solve, the lowly lichen properly deserves a greater deal of reverence before we bash it into posterity.

There are an estimated 13,500 species of lichen found on earth, of which more than 10,000 are the crustose kind, that is, the kind that grow on rock surfaces, walls, and tombstones. These grow so tightly encrusted into the rock surface that they are nearly impossible to pry off. The kind of crustose lichen that resembles in shape, say, a map of Australia, is called a “map lichen” or to put a Latin spin on it, Rhizocarpon geographicum.

A lichen is a most amazing sort of organism: it is a symbiotic mix of algae and fungi. The fungus provides the skeletal structure for the algae and is the member that digs minerals out of the host rock surface to supply nutrients. The algae-partner contributes photosynthesis that cooks food for the team. The specific mix of fungi type with algae type defines the species.

The speed at which map lichens grow is, well, even slower than geologic in rate. Rarely do these organisms enlarge in diameter more than 1mm/year, while tectonic plates race around at 3 – 6 cm/year. The age of a particular map lichen colony can be estimated from its size; this is so useful to estimate the ages of a geomorphologic or archeological surfaces that it provides the basis for a kind of dating by “lichenometry.” Since lichen cannot subsist in polluted conditions, most particularly they cannot abide air pollution whether by human or volcanic source, the map lichens map out, so to speak, the evolution of an exposed earth and its climatic conditions. They have proved invaluable in the study of glacial advances and retreat.

By their sizes, it would seem that lichens can live thousands of years, indeed the oldest recorded colony is found in the arctic and is estimated to be nearly 9,000 years in age. And it is still doing fine though it perhaps misses the mammoths that were prevalent in its youth. Some scientists question whether lichens could be immortal. Quite possibly, given the proper non-polluted environment and escaping the rock hammer of a geologist, map lichen could live forever. In a space experiment, lichen was exposed to outer space for fifteen days (yes, fifteen days!) and when returned to Earth, it appeared to have suffered no adverse effects. To quote Dr Frankestein, “It’s alive!” – ( http://tinyurl.com/5fsnjk )

Let’s point out again for emphasis – a lichen can do a harsh environment, even survive the rigors of space. But it can’t do air pollution. The study of map lichen population and changes in species is a way to measure changing air quality in a wilderness area.

Though rare in the fossil record, mainly because of their low chance of preservation in the rock record by those fast-moving geologic processes, some lichen-like fossils date to the early Proterozoic (2.2 – 2.7 billion years in age). The late Precambrian Edicaran fossils have also been speculated to include lichen. The oldest near certain fossil lichen dates to the Devonian (400 million years in age). There is speculation that lichen-like organisms, extracting minerals from rocks to produce fertile soils, preceded and were essential for the advent of plants into the terrestrial environment.

Map lichen can be just about any color – yellow, rust, sage, grey, pink, black, ecru. In some cases their color contrasts vividly from the rock surface they are found on, and in other cases they seem camouflaged with the rock. In a lichen-rich part of northern Greece, map lichen occur that mimic the appearance of a fresh rock surface: I mention this because I have found it annoying to see what looks like a “fresh” rock some hundred or more meters above the trail on the hillside, then after hiking up to take a look, find out it’s, yup, that annoying lichen once again.

I’m not going to say that I regret having bashed the map lichen surfaces into smithereens while trying to collect a rock sample, but at least I can bow my head in reverence to these organisms that possibly once witnessed Alexander the Great on the trail below them.

Annie R

Photo: By me and Anna Batsi. The map lichen is sat on by a lizard sitting on outcrop of what is one of the oldest rocks of Greece at 700my in age.

http://blogs.smithsonianmag.com/smartnews/2013/01/lichens-do-not-age/

http://www.countrysideinfo.co.uk/fungi/lichens.htm

http://www.ucmp.berkeley.edu/fungi/lichens/lichenfr.html

http://www.grida.no/photolib/detail/map-lichen-rhizocarpon-geographicum-setesdalheia-norway_3df8

http://www.nps.gov/glac/naturescience/lichens.htm http://www.projectnoah.org/spottings/15190063http://www.wnps.org/blog/tag/map-lichen/

Dating of rock lichens: http://www.scahome.org/publications/proceedings/Proceedings.11Kodros.pdf

http://www.primaryresearch.org/stonewalls/nylund/