Likin' the Lichens

Not a real leaf today and also not actually a plant. We're talking about Lichens.

'Lichen' is a term applied to range of composite organisms formed by the symbiosis of a fungus and a photosynthesising green alga or cyanobacterium. They come in many colours, sizes, and forms. 

They may have tiny, leafless branches (fruticose). Or they might have flat leaf-like structures (foliose); or look like a crust adhering tightly to a surface (substrate) or like a thick coat of paint (crustose). Or

they may have a powder-like appearance (leprose). 

Generally, most of a Lichen's bulk is made of interwoven fungal filaments, but this is reversed in some filamentous and gelatinous Lichens.

There are about 20,000 known Lichen species but 'species' is a difficult thing to quantify as they are composite organisms. By convention they are classified according to the species of their fungus, not by the species of the algae or cyanobacteria. 

Their lineage is difficult to follow too. Because Lichens are combinations of members of two or even three different biological kingdoms, these components all have a different ancestral lineage from each other. 

Lichens are long-lived but lifespans are difficult to measure because what defines the 'same' individual Lichen is not precise. Lichens grow by breaking off a piece, which may or may not be defined as the 'same' Lichen. The two can also sometimes grow and eventually re-merge to make one much larger 'same' Lichen. However, an Arctic species called 'Map Lichen' (Rhizocarpon geographicum) has been dated at 8,600 years old, which has a good claim on being the world's oldest living organism.

They're also hugely successful and cover about 7% of the planet's surface. They are found on almost any surface and in all habitats, including some of the most extreme conditions on Earth. They can even live inside solid rock, growing between the grains. Some lichens do not grow on anything, living out their lives blowing about the environment, and two species have evolved to live underwater.

Wherever they grow, they create fascinating patterns and patination. Just last week I spotted a young Lime tree that, during its early growth, was supported by a stake and a webbing belt. The belt was recently removed showing what the bark would look like if Lichens hadn't colonised the trunk. The second photo is of another Lime tree that's a year or so older.

Some Lichens are poisonous to eat and, helpfully, most of the dangerous ones are coloured yellow. However, some are edible. Oakmoss (Evernia prunastri), for example, grows primarily on the trunks and branches of oak trees, but is also commonly found on the bark of other deciduous trees and conifers such as fir and pine. The Lichen has a distinct and complex odour and can be described as woody, sharp and slightly sweet and Oakmoss growing on pines has a pronounced turpentine odour that is valued in certain perfume mixes. It is commercially harvested in countries of South-Central Europe and usually exported to the Grasse region of France where it is used as a perfume fixative and to form the base notes of many fragrances.  

It's also featured on the menus of several top-end restaurants in recent years, including Heston Blumenthal's The Fat Duck.

Photo by Liondelyon (Creative Commons)

Photo: Enthusio Chefs (Creative Commons)

The Fat Duck's dish 'Oak Moss' is described as: 'Jelly of Quail, Crayfish Cream, Chicken Liver Parfait and Truffle Toast. Thin sheets of oak-flavored film are presented on a bed of oak moss which are dissolved on your tongue. Scented liquid nitrogen is then poured over the moss from an arare iron teapot, filling the air with the aroma of an oak forest and producing the effect of morning fog.'

I'm 'lichen' the sound of that.