Something that people see a lot of but perhaps don't give it much thought is lichen.
Lichen is a composition of fungi and algae. They are not considered plants even though many resemble them with leaves and even branches.
Lichen can grow on almost any surface and at nearly any elevation from sea level to mountain alpine regions and can even grow on other lichen.
There are around 20000 known species that cover 6-8% of the Earth's land area.
Lichens are very long lived with an Arctic species dated at 8600 years old.
Like the Tardigrades covered in a previous blog here they can also live in extreme conditions of heat and cold and have even been subjected to conditions in space with no ill effects.
Although able to cope with such extreme conditions some lichen are sensitive to pollution as they have no roots and no way to filter what they absorb so if there are pollutants in the air it can accumulate in the lichen which can become toxic although not all lichen are sensitive to air pollution.
More information on lichen can be found on the links below.
By Brendon Crook