What is it? A close look at the strange yellow stain on Maltese stone

Ever wondered what those strange yellow and white stains on Maltese rock are? It looks like some kind of moss but flatter and harder. Well, welcome to one of the most interesting organisms on the planet. The Maltese Environment and Resources Authority (ERA) describes them as “important, but poorly known, biodiversity components of the Maltese Islands.”

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A post shared by @laflexviking on Jan 14, 2019 at 5:00am PST

Maltese lichen looks like a flakey yellow or white growth usually covering large areas of rock. Xanthoria parietina is commonly known as maritime sunburst and it sure looks like a sun when it grows in circular patterns.

Isn't it wonderful how nature tends towards creating spirals?

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Lichen is actually made up of three distinct organisms that combine to create a symbiotic existence as a single organism. A fungus, an alga or cyanobacteria, and basidiomycete yeast join in a mutually benefiting relationship for all individuals.

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The alga or cyanobacterium convert energy from the sun and carbon dioxide into sugars through photosynthesis, producing food. The fungus forms the main structure of the lichen, absorbs and stores water in its hyphae, and protects the alga from dehydration and the environment. Basidiomycete yeasts - single-celled fungi - produce chemicals that ward off predators and repel microbes.

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Lichen grows on any surface that provides the right conditions for its survival, be it rock, branches or a metal railing. Not having roots or leaves, lichen absorbs nutrients directly through their surface. It is therefore susceptible to air pollutants which ac­cu­mulate in their body and eventually kill them. The presence of lichens is a direct indicator of good air quality while dead lichens are a sign of pollution!

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When you're next out on a walk, whether in an urban area or in the countryside, keep your eyes keen to spot lichen and, this time, give it a really good look!