Lovable lichens: Strange plants are sign of a city’s improving air

PUBLISHED: 10:22 08 February 2019 | UPDATED: 10:22 08 February 2019

An evernia lichen on a branch in the Heath Extension. Picture: City of London Corporation

An evernia lichen on a branch in the Heath Extension. Picture: City of London Corporation


Over the years, you may have noticed an increase in lichens on the Heath.

Lichens are indicators of improving air quality. Picture: City of London CorporationLichens are indicators of improving air quality. Picture: City of London Corporation

They are intolerant of atmospheric pollution, so the Clean Air Act and the rise of low-emission zones have come in handy.

The Heath, managed by the City of London Corporation, boasts more than 50 species of lichen in 2019 – an encouraging stat given it’s surrounded by one of the world’s busiest cities.

Lichens were viewed with great curiosity before the middle of the 19th century, because no one knew how to categorise them.

They are strange composite organisms, with two or sometimes multiple species living together in a complicated entwined relationship. Often, this is between fungi, photosynthetic algae and bacteria.

An opal lichen. Picture: City of London CorporationAn opal lichen. Picture: City of London Corporation

The role of bacteria within lichens is still poorly understood and was only recently discovered.

But a close association with a fungal partner could allow the bacteria to endure habitats that would otherwise be too harsh for survival.

It is the fungus that makes up the main body of the plant in which the algal cells can be found. These cells provide nutrition for the fungus through the photosynthetic process and the fungus procures moisture and nutrients from the surrounding environment.

On the Heath they are not found everywhere. The acidity or alkalinity of the trees’ bark (the substrate) dictates which lichen species can be found.

The Heath’s willow and oak trees are the most popular for lichens.

They can be very robust, too, and occupy a range of habitats from Arctic tundra to sun-drenched deserts.

In fact, some lichens are so robust that they managed to survive for 18 months being bombarded by radiation strapped to the outside of the International Space Station as part of an experiment investigating the transfer of life between celestial objects.

The growth rate of lichens is very slow compared with many other terrestrial species and can vary from 1mm to 1cm per year depending on the species, temperature, available moisture and substrate (their host).

They can, however, be very long-lived – some Arctic species could be more than 8,000 years old!

Find out more at the British Lichen society website:

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