Licheni

Licheni, in Romanian terminology for the organism known in English as lichens, are composite organisms resulting from a close symbiosis between a fungus (the mycobiont) and a photosynthetic partner (the photobiont), usually green algae or cyanobacteria. In this partnership the fungal partner provides structure and protection, while the photobiont supplies carbohydrates through photosynthesis. The combined entity forms a thallus that can be crustose, foliose, or fruticose in shape.

Lichens inhabit a wide range of environments, from rocks, bark, and soil to deserts, tundra, and alpine zones. They are often among the first colonizers of bare substrates and contribute to weathering and soil formation by producing organic acids. Growth rates are typically slow, with many lichens expanding only a few millimeters per year.

Reproduction occurs primarily through fungal sexual spores, but lichens can also propagate asexually via structures such as soredia and isidia, which contain both fungal and photobiont partners. Diversity is high in boreal and alpine regions, tropical montane areas, and coastal habitats, where different thallus forms—crustose, foliose, and fruticose—adapt to microhabitats.

Ecologically, lichens are important bioindicators of air quality because many species are sensitive to atmospheric pollutants. They have applications in environmental monitoring and traditional uses in dyes and medicines. Taxonomically, the mycobiont is typically an ascomycete, with green algae or cyanobacteria as the photobiont.

Fossil evidence suggests lichens have a long history, with records dating back hundreds of millions of years, underscoring their resilience and ecological role across Earth’s climates.