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Lichen on Trees

Posted in Garden Advice on July 26, 2017


Lichens on trees are harmless but some may consider them unsightly. How to identify lichen and what lichen on tree bark means and, if necessary, how to get rid of lichen.

Lichens are symbiotic organisms, i.e. they are a combination of algae or cyanobacteria and a fungus. The two organisms grow together in a symbiotic relationship; each deriving benefit from the other. The algae or cyanobacteria can photosynthesise and produce food using light which they pass on to the fungus. The fungus protects the algae or cyanobacteria and gathers moisture and nutrients from the environment which they pass on to the algae or cyanobacteria.

Lichens come in various colours including green, grey, orange, yellow, black and more. They also come in a variety of forms including multi-branched tufts, flat leaf-like structures, crusty coatings, powder-like coatings, jelly-like and others. Most are low growing and tight to their substrate. They don’t have roots but fix themselves tightly to their substrate. Lichens are very slow-growing and are thought they can live for hundreds, perhaps thousands of years.

Liverworts can look similar to lichens but liverworts are true plants and are not a symbiosis of algae and fungi.

Lichens are remarkable for their ability to survive in the harshest conditions where other organisms would struggle; rocky seashores, arctic tundra, deserts, roofs, asphalt driveways and tree bark among others.

Many lichens are epiphytes; growing on the exterior of plants. On trees lichens, do not cause harm to the tree, they are not parasites and do not consume any part of the tree. They are commonly found growing on the bark of older trees. Some regard the lichens as attractive additions to the tree, but others regard them as unsightly and want to remove the lichen to leave the tree bark clean.

Should you wish to remove lichen from trees or other plants they can be sprayed with Kiwicare Organic Super Sulphur. The tough nature of lichens means that even when dead they will take some time to deteriorate and fall off the tree.

Lichen can be removed from hard surfaces such as driveways, paths, headstones, roofs, using SORTED Moss and Mould cleaner.

David Brittain

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