What do the terms phycobiont and mycobiont signify?

The terms phycobiont and mycobiont are used to describe the two distinct components of a lichen, which is a symbiotic association between a fungus and a photosynthetic partner.

• Phycobiont : It is the algal component of lichen. It is usually a green alga (like Trebouxia or Trentepohlia) or a cyanobacterium (such as Nostoc). This component is responsible for producing food through photosynthesis, providing carbohydrates and other nutrients that are shared with the fungal partner. The phycobiont plays a crucial role in the survival of the lichen, especially in harsh environments, by supplying energy.
• Mycobiont : It is the fungal component of lichen. It is typically an ascomycete or, less commonly, a basidiomycete fungus. The mycobiont provides structural support and protection to the phycobiont by forming the lichen's body, or thallus. It helps the lichen retain water, shields it from environmental stress, and enables the association to grow in diverse habitats.
• Significance : Algae prepare food for fungi in turn fungi provide shelter, mineral nutrients and water for algae.

This mutualistic relationship allows lichens to thrive in extreme conditions, such as on rocks, tree bark, and in deserts. Both the phycobiont and mycobiont depend on each other for survival, making their partnership a remarkable example of biological symbiosis.