How are lichens classified?

Lichens are regarded by scientists as fungi with an unusual method of nutrition (although with 40% of ascomycete fungi being lichenised, it is not that unusual).

About 20 different types of algae and cyanobacteria are involved in the lichen symbiosis, but they can also live independently. In contrast, the thousands of different fungi associated with them in the lichen symbiosis cannot thrive in the absence of their algal/cyanobacterial partner, forming merely a shapeless mass of fungal hyphae.

However, the combination of mycobiont (fungi) and photobiont (algae/cyanobacteria) gives the lichen body a structure and complexity not encountered in either partner on its own.

Hypotrachyna revoluta, Xanthoria parietina & Physcia tenella © Robert Thompson Ochrolechia androgyna © Robert Thompson Ramalina fastigiata © Robert Thompson Porpidia crustulata © Robert Thompson