#lichenometry

I usually use google scholar for my lit searches, but that's just me. Lichenometry is a tricky subject and its efficacy has come into question in recent times. I pulled up some papers on it for some students who were curious about it earlier this year: Limits to lichenometry

Modeling Uncertainties in Lichenometry Studies

Rusavskia elegans 

Elegant sunburst lichen

This gorgeous specimen is a foliose lichen that is easily recognized by its color, shape, and tendency to grow in large colonies even in harsh conditions. In fact, R. elegans is world famous for making a trip to nowhere other than the International Space Station and surviving the hostile conditions of outerspace for 18 months! (source) That bright orange color is due to mutatoxanthin caratoanoids which are chemical compounds that help protect this lichen from extreme UV radiation. This protection helps this lichen to grow on sun exposed rocks (and bones as seen above) and and human-made surfaces. Its amazing ability to survive has helped in its quest for world domination, and it can be found all over the world. R. elegans is often used for lichenometry, i.e., using lichens to estimate the age of rocks. By knowing the approximate rate of growth, scientists can measure the diameter of the lichen rosette on a rock-face and get an idea for how long it has been growing in that location, and therefore how long that area has been exposed. On another note, this lichen is still often referred to by its synonym Xanthoria elegans. I can’t find information on when and why the name change took place, so *shrug*

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Rhizocarpon geographicum

Map lichen 

Meet the OLDEST LIVING ORGANISM ON EARTH: R. geographicum! That’s right! Using lichenometry (measuring the diameter of a lichen that has a known and constant growth rate to determine its age), scientists have aged some Arctic individuals at 8,600 years old! (well, ok, new research has shown that these estimations are maybe not as reliable as we once thought, but it’s still really really old) This distinctive crustose lichen is made up of round or angular neon green/yellow areoles tightly grouped together in patches surrounded in a black prothallus. Scattered among the areoles are black apothecia that are usually a similar size and shape to the areoles, giving the entire thallus a mosaic-like, tiled appearance. The patches tend to grow in large colonies across rock surfaces, which ends up giving the rock a map-like appearance! It colonizes siliceous rock in open, high-mountain sites, often near of above the treeline. It has a world-wide distribution, but is only found in some of the most isolated and freezing cold environments so it is not common. If the extreme age of this lichen isn’t enough to amaze and astound you, you should also know that R. geographicum is one of the lichens that has survived exposure to the vacuum of space! Basically, this lichen is a beautiful badass who is cooler than you will ever hope to be. Die mad about it. She will outlive you a hundred times over and laugh as your weak flesh succumbs to decay. 

images: source | source | source | source

Candelariella vitellina

This crustose lichen is made up of granules or areoles that can appear scattered or more crowded together, often forming thick, continuous patches. Individual areoles are flat or convex, irregularly shaped, and green-yellow to orange-yellow in coloration. Lecanorine apothecia are common, and the disc can be flat to convex, and concolorous or slightly darker than the main thallus. The apothecia often have a visible exciple (lateral layers on the underside of the apothecia that lack algal cells), a distinguishing characteristic. C. vitellina is not so picky when it comes to habitat, and can be found growing on acidic rock, and on wood and bark around the world. This lichen is a great one to find in your local area as it is common and widespread. Plus it has that bright color that makes it particularly visible! One cool study looked at specimens of C. vitellina growing on tombstones in an old Scottish cemetery, and they used the date when the tombstone was erected (*cough cough* you know, the death date) to measure rates of colonization! And hey, what better to isolate yourself can you think of than to go one a graveyard lichen hunt? 

Placynthium nigrum

Blackthread lichen, ink lichen

Let’s face it: we all had some sort of goth phase. I too had my share of Hot Topic t-shirts and safety-pinned hoodies. I am sure some of y’all pulled off the look much better than I did. But I doubt you ever looked as good in all black as P. nigrum does! This crustose lichen is made up of tiny lil irregular squamules which can appear more scattered and areolate, or thick and felt-like. The upper and lower surfaces are dark brown or black, surrounded by an inky blue prothallus. The surface is covered in nodular isidia, and round, dark apothecia. P. nigrum colonizes limestone and other calcareous rocks, and can be found more rarely on soil. She even goes so far as to colonize old gravestones. Yep, she’s not some poser. She’s got real darkness in her soul. P. nigrum can be found throughout the northern hemisphere, where she brings a touch of beautiful darkness wherever she goes. 

Every day has its designated flower in the language of flowers. The flower for today, November 12, is Lichen, which signifies solitude. Image above from Wikipedia. A Lichen is a composite organism composed of a particular fungus and a particular alga growing in an intimate symbiotic association and forming a duality, commonly adhering in colored patches or spongelike branches to rock, wood,…