LICHEN ACIDS & METAL SEQUESTRATION
Usnea Flammea contains the Orcinol Depsidones: Lobaric Acid and Stictic Acid.
Doing the K Spot test with KOH results in a yellow to red transition if Stictic Acid is present, as it usually is. p-phenylenediamine test (Pd test) gives a positive result on Stictic Acid by turning orange.
Lobaric Acid is only present in 80% of specimens tested, but if present, it is present in only Usnea Flammea and in no other Usnea species.
Other accessory Lichen Acids are Norstictic Acid and Menegazziaic Acid.
These lichen acids bear many chemical similarities to Usnic Acid which is found in
Cladonia arbuscula and in
Norstictic Acid has rather special properties amongst Lichen acids which the closely related Stictic Acid lacks: it can (and within lichen species possessing it, does) sequester metals. That single change from the -O- group of Stictic Acid to the HO- group makes all the difference to Norstictic Acid. If the lichen happens to be growing on a copper mineral, then copper can be sequestered by the lichen, changing its colour (in the case of copper, to green). The colur change is so strikingly distinctive that lichenologists have previously mis-identified them as different species of lichen. Previously, the colour of all lichens was attributed to the normal colourful organic lichen pigments, but now several species of lichen have been found where the primary colouring agent is from heavy metal sequestration. Other metals can be similarly sequestered. Thrift also has mechanisms for heavy metal sequestration.
Some lichens, such as
Lecanora cascadensis, can accumulate up to 5% of copper (dry weight). The colour varies from light green (1% copper) to a darker malachite green at 4% copper. Another lichen,
Acorospora rugulosa was found to contain 16% dry weight in copper, which was affixed outside the cells rather than within them. A recently discovered, and very rare, copper sequestering lichen (
Lecidea inops) has recently been discovered growing on the extensive copper ore tailings from both ancient and more modern copper mining in the Coniston Copper mining valley. It is very rare.
Many lichens grow on a diverse range of toxic heavy-metal containing substrates, containing ores of lead, copper, uranium and arsenic. In some lichens, the oxalates of metals such as zinc, manganese, copper, lead and magnesium are to be found within them.