This is an article I found from NZGeo a couple of months ago that I keep coming back to :) it's worth a read in full, but below are some of my favourite segments from it:
"Lichens are a world unto themselves, almost invisible, yet after you notice one, you see them everywhere. They grow on the summit rocks of Mt Cook and on river stones, on fences, walls of old houses and bark of trees and their leaves, on tarmac and pavements, even on glass, gravestones and old cars. There are more than 18,000 known species in the world (and researchers suggest there might be as many as 24,000) yet there is just one common word to describe this incredible diversity of life: lichen. They are diverse in form and design. Rhizocarpon geographicum, for example, forms vivid patches whose beauty and complexity echo satellite images of the Earth. Graphis librata resembles hieroglyphic writing etched into tree bark, while the high-alpine Xanthoria elegans grows in colourful patterns which bring to mind Aboriginal paintings. Lichens are one of the planet’s most successful colonisers but are unlike other forms of life on Earth. They are not plants but composite structures, miniature ecosystems comprised of fungi and photosynthetic partners—usually algae or cyanobacteria, sometimes both. Traditionally, this arrangement has been considered symbiotic but some lichenologists suggest it is not true symbiosis—the algae can survive without the fungi but not vice versa. Fungi capture the algae with their web-like filaments and cultivate them as a farmer would a crop. The fungi do not pass any nutrients back to the algae, but in return for “milking” them of carbohydrates they produce, the fungi protect the algal cells from mechanical damage and excessive sunlight and keep them moist. Whatever its definition, the fungi–algae arrangement has been so successful that nature has chosen this evolutionary path not just once, but several times independently. The partnership is stable and resilient and not only allows the fungi and algae to survive together where on their own they would surely perish, but makes it possible for lichens to flourish in environments we think of as hostile."
"Laboratory tests have demonstrated that lichens can be dry-frozen to temperatures nearing absolute zero (minus 273ºC) and then warmed back up again without any ill-effects. They have also survived irradiation of 1000 rads per day for two years, and continued to grow, while a single exposure of 400 rads is fatal to a human. Perhaps the most striking example of their ability to survive the extreme conditions was the experiment conducted by the European Space Agency. In May 2005, two species of lichen, the aforementioned R. geographicum and X. elegans, were sealed in a capsule and launched into space on the Russian rocket Soyuz. Once in orbit, the capsules were opened and the lichens were exposed to the vacuum of space, its near-absolute zero temperature and the complete spectrum of ultraviolet light and cosmic rays. After 15 days, the lichens were brought back to Earth. They were found to be in perfect health, with no discernible damage from their time in orbit."
"...lichens exist on a timescale completely different from ours... Some New Zealand lichens can grow as much as 1–2 cm a year, but there are others which manage only 0.02–2 mm of radial growth per year, and this makes them perhaps the slowest growing of all known organisms. When you consider the size of the largest known specimen, they could well be over 5000 years old, surely among the oldest living organisms on Earth.”
"The sombrero-shaped Rangitoto, the youngest, largest and least-modified cone in the Auckland Volcanic Field, came into being during a series of eruptions between 600 and 700 years ago. Despite appearing green from the distance, up-close it is still a harsh and raw-looking place, made up of sharp black basalt and lava stones called scoria. It is also exceptionally arid, as there are virtually no water catchments and lava fields are poor at retaining rainfall. In short, Rangitoto is an ideal habitat for lichens, so it’s little surprise that some 194 species—one of the country’s highest diversities of lichens—have been recorded here. Walking the trails of Rangitoto is like watching the history of plant settlement in fast-forward. Barely did the lava begin to cool than the first wind-born spores of lichens arrived, anchoring into the porous new world. For many years, centuries perhaps, the rocks would not have looked much different—just tiny splodges of paint-like growth, velvet or crust here and there; green, black, white or vividly yellow where the eye-catching Xanthoria ligulata had colonised. But spreading imperceptibly, growing, dying and decomposing, the lichens built the foundation for life, the first thin layer of soil. Into it, airborne dust and guano from seabirds added nutrients and depth and, with time, more complex lichens arrived, then mosses and ferns. Follow this ecological trajectory and, in the case of Rangitoto, a few hundred years later you have the largest stand of pohutukawa in the world, laced with ferns and orchids. All told, more than 200 species of trees and flowers stand in a place that was once barren and sterile rock."
"...the lowly lichen, rustici pauperrimi—the poor little peasants of nature—as Linnaeus called them in his 1753 book Species Plantarum. They not only become soil and humus, they actively create it. Their hair-like rhizines, despite their tiny size, can exert enormous pressure on the rock to which they anchor, and they don’t just grow over rocks, they grow into them as well. In some species the rhizines can penetrate the rock to a depth of 6–8 mm, and the oxalic acid within them reacts with most metals and minerals until it is impossible to tell where the rock ends and the lichen begins. In this way lichens stabilise the soil on which they grow, binding pebbles and organic matter, preventing erosion by wind and water."
The advantage of studying lichens in cemeteries is that they are conveniently dated... Measuring the size of lichens and estimating their age is called lichenometry. The method is not infallible (since two or more lichens can grow into one another, fuse, and give a false estimate), but knowledge gleaned from cemeteries is valuable in the field as a quick and cost-effective way to date rock surfaces to determine, for instance, the retreat rate of glaciers. “In effect, lichens change an inorganic environment into an organic one... and that, if you think about it, is a miracle of life in itself. But they don’t stop there. They are also one of nature’s best healing agents. Like raw honey we used to put on cuts and abrasions, lichens appear on wounds in the earth and seal them, until the skin of life grows over them again.”
Above: A lithograph from German biologist Ernst Haeckel’s 1904 collection "Artforms of Nature"
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