Algae: A green film or powdery deposit is typical of algae on paving, stonework and garden furniture. The dark green or blackish jelly-like growths that often appear in damper, cooler weather on paths and areas of tarmac are incorrectly known as blue-green or gelatinous algae, but are in fact Cyanobacteria.
Lichen: These are common on paving and timber structures such as garden benches. The colour of lichen varies with species, but most are silver-grey, grey-green, yellow or orange. They can...
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