what are Lichens?

Symbiotic Relation
in Lichens

Lichens are members of fungi. They are characterized by forming symbiosis with algae. When a fungus forms a symbiotic organism with an alga, it creates a peculiar body called "thallus". Fungi (mycobionts) and algae (photobionts) that compose lichens help each other to survive. In return for the stable housing and water supply that the fungi provide to the algae, the mycobionts receive nutrition (carbohydrate) that the algae produce by photosynthesis.@Their symbiosis is so tight that its shape, physiological function and distribution are genetically inherited just like an independent plant.
Lichens are widely distributed all over the world. In Japan alone, more than 1800 species are known to exist. They normally grow around us, but since many of them are vulnerable to air@pollution and slight changes in their habitat, they are rapidly withdrawing from big cities. However, away from those urban areas, in forests and high mountains, we can see lichens beautifully covering the surface of the earth and rocks and tree trunks.

œfig.1: Lichens in the Sonora Desert, Mexico

‘Plants easily mistaken as lichens

Hepaticae and mosses
Body cell Cells of fungi and algae Cells containing chloroplast Hyphae without chroloplast
Shape No clear distinction between stems and leaves
Crustose, fruticose, and foliose thalli
Clearly defined stems and leaves
Cormus , thallus
Without leaves or stems
Forms mass of hyphae (mycelium), mushrooms,etc.
Color Mostly gray or light green, exceptionally orange Greenish Varied
Yellowish ocher
Brown, etc.
Or colorless
How they
By ascospores, soredia, isidia Mainly by spores By spores, pycnoconidia, etc.
Classification The fungi (symbiotic organisms with algae or cynobacteria) Green plants The fungi