Know Your Lichens- Episode 2: Elegant Xanthoria, Colour Changing Nitrophile
In our first column, we learned that lichens are useful monitors of pollution and play a richer role in the cycles and survival of ecosystems than their humble appearance suggests. But what ARE lichens exactly? You’d be forgiven if you thought they were some sort of ancient plant, and also half right. Between 400 and 700 million years old, lichens are ancient and in fact a major part of the earliest colonization of life on land. Acids they secreted on rocks to bond and cling to their substrate slowly ate away at the mineral and helped create the first plant-life supporting soil.
Lichens themselves are a pre-historic survival strategy gone so right they’ve survived millennia as life around them kept evolving, and by now seen downright alien to the modern classification of life forms. Not one single organism, they are instead a composite of one or more fungi and one or more algae or cyanobacteria. The fungi provides a home and shelter from the elements for the algae or cyanobacteria, who in turn provides food through photosynthesis as it’s part of the partnership. As they can not make their own food from sunlight fungi are not plants and are, bizarrely, closer on the tree of life to the animal kingdom.
Hence lichen have been described in short as ‘when fungi learned to farm’ or ‘when fungi went solar’, but this unique adaptation has made them successful extremophiles, able to live in the arctic, desert and other harsh environments where little else can. There has even been talk of sending them to Mars to help establish life as we know it there. The same pigments which make lichens powerful and alchemical dyestuff are responsible for providing protection from the sun’s rays to the algal partner. Even ultra hardy lichens like Xanthoria, which positively loves nitrogen and can thrive amidst all sorts of toxins including heavy metal contamination, still avail of this brilliantly coloured chemical sunscreen to keep the food-producing algae safe.
Sunshiney yellow to orange-red, Xanthoria is most familiar to Newfoundlanders on rocks around the ocean and on gravestones, and one common name is Maritime Sunburst Lichen. Large cup-like structures are often present on the lichen body. Folk uses include blending with a special red wine to ease menstrual cramps in Andalusia or fermenting in an ammonia mixture to create a fabulous magic trick of a dye for wool and silk. Called photoreactive dye, the pigments change colour when exposed to the suns rays. Fibre dyed with Xanthoria will come out of the dye bath pink but over several minutes in sunlight will change to an icy blue.
Along with the Rhizocarpon grouping, to which the uber common green and black map lichen adorning local cliffs belongs, Xanthoria is among the most useful lichens for a method of dating exposed rock and markings on exposed rock called lichenometry. Assuming a certain rate of growth for specific lichens, measurements of lichens can give insight into how long a rock face has been exposed or marked. With a practical limit of 4000 to 5000 years, lichenometry is most accurate within 1000 years and of greatest use when used for rock faces exposed or marked for 500 years or less. Lichenometry can provide information on past geological events and help track climate change in the present.
If this makes you ask, “well how damn long do lichens live then if you can date a specimens growth for 5000 years?!?” Tune into the last installment of Know Your Lichens to find out the answer.