Lichen. Light micrograph of a section through tissue of a lichen. Lichens are symbiotic associations of a fungus (the mycobiont) with a photosynthetic partner (the photobiont). Here, cyanobacteria (formerly known as blue-green algae) are seen as dark red dots within a loose mass of fungal hyphae (green). The fungus benefits from photosynthetic activity of the bacteria and the bacteria may take advantage of the protection it obtains from drought and intense light. Lichens are slow growing organisms and colonise rocks, tree trunks and soil.