What are the best known examples of symbiotic relationships you know?

The symbiotic relationship in which there is a stable mutually beneficial coexistence of two organisms of different species is called mutualism. Such, for example, are the relationships between the hermit crab and sea anemone or highly pollinated plants with the insect species pollinating them (clover and bumblebee). Cedar pine, eating only the seeds (nuts) of cedar pine, is the only distributor of its seeds. Mutualism is very widely developed in nature.
In fact, symbiosis is an inseparable, mutually beneficial relationship of two types, implying mandatory close coexistence of organisms, sometimes even with elements of parasitism. A classic example of symbiosis is lichens, which are a close mutually beneficial cohabitation of mushrooms and algae. Thanks to symbiosis, lichens have reached a high species diversity (more than 20 thousand species) and gained the ability to live in the most severe conditions: in the polar regions, on bare rocks, on the bark of trees, in high mountains. Typical symbiosis is the relationship between termites and flagella, living in their intestines. These protozoa produce an enzyme that breaks down fiber into sugars. Termites do not have their own enzymes for the digestion of cellulose and would have died without symbionts. And flagellates receive favorable environmental conditions in the intestine and do not occur in nature in a free state. A well-known example of symbiosis is the coexistence of green plants (primarily trees) and mushrooms.