Most of us have likely spotted mosses and lichens growing on trees at some point. They can have vivid colours, and are especially visible during the winter months when most deciduous trees have lost their vibrant colours. But have you spotted their shyer cousins, the algae?
You probably associate algae with large water bodies, but some species are terrestrial. In the UK, we have many varieties that grow on trees, often visible as a green or red film on tree bark.
Red algae come from a group of algae called Trentepohlia. These species of algae appear on trees (and some other outdoor surfaces) in quite bright colours, ranging from orange through to a rusty red. The orange colour is caused by the pigment in the algae, which is a carotenoid – the same thing that makes carrots orange.
Where to find algae
Like lichens, algae are sensitive to moisture. They are therefore more likely to be found on rough, textured bark, where rain gets trapped and an ideal damp habitat is created. It’s predominantly associated with oak, ash and beech, and is more common in the south of the UK.