Lichens symbiotic close

Lichens are a symbiosis between fungi and algae or cyanobacteria, serving as pioneer organisms in diverse environments.

About this subject

Lichens are composite organisms formed by a symbiotic association between a fungus (mycobiont) and one or more photosynthetic partners (photobionts), usually green algae or cyanobacteria. This mutualistic relationship allows lichens to colonize extreme surfaces such as bare rock, tree bark, and poor soils, making them pioneer organisms in ecological succession. There are an estimated 20,000 lichen species worldwide, distributed across all biomes from hot deserts to polar regions.

Lichens are sensitive to air pollution, especially sulfur dioxide, and are widely used as bioindicators of air quality. Some species, like Usnea (old man's beard), are known for medicinal properties and have traditional use in respiratory infections. Additionally, lichens have historical importance in producing natural dyes, such as litmus used in pH indicators, and in perfumery, for example oakmoss (Evernia prunastri).

Lichen reproduction occurs mainly through fragmentation of the thallus or dispersal of soredia and isidia, structures containing both symbionts. Although they grow slowly, some lichens can live for centuries, with records of specimens over 4,000 years old in the Arctic. The lichen symbiosis is so integrated that the fungus often cannot survive without its photobiont, demonstrating highly specialized coevolution.

Frequently Asked Questions

What are lichens?

Lichens are organisms resulting from a symbiosis between a fungus and algae or cyanobacteria. This association allows them to live in extreme environments.

Why are lichens used as bioindicators?

Because they are sensitive to air pollution, especially sulfur dioxide, their presence or absence indicates atmospheric quality.

How long can a lichen live?

Some lichens can live for thousands of years; the oldest known specimen is about 4,000 years old and found in the Arctic.