When we think of Fungi the usual things that spring to mind are mushrooms, but there actually over 100,000 species of fungi known to us and it is estimated that in total, about 1.5 million species exist on earth.
Fungi grow and spread fast, they can cause infections such as gangrene and are currently responsible for wiping out almost a third of the worlds amphibians.
They are deadly, tasty and vital to our global food web. When an organism dies, whether animal or plant, fungi feed on it. Through feasting on dead remains fungi convert organic matter into soil, without it our planet would be covered in dead material and nothing knew could ever grow.
From Crash Course: Biology on YouTube presented by Hank Green.