Kingdom Fungi
This is the kingdom of unicellular or multicellular fungi, made of eukaryotic cells with cell walls containing chitin.
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Fungal species are thought to number between 1.5 million and 5 million. They have very small structures.
As decomposers
These organisms make a special contribution to the decomposition of organic matter.
As partners
They also form symbiotic associations with other organisms — the lichen is one.
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A fungus is not a plant
Mushrooms grow out of the ground, which makes them easy to take for plants. But a fungus has no chlorophyll, so it cannot make food; and its cell wall is not cellulose but chitin — the same material as an insect's exoskeleton.