Cyanolichens: An Evolutionary Overview

Abstract

Lichens are self-supporting and ecologically obligate associations between symbiotic fungi and green algae and/or cyanobacteria. The term ‘cyanolichen’ refers to all lichens with cyanobacterial symbionts, either as the sole photosynthetic component or as the second photobiont in addition to the primary photobiont (eukaryotic algae). Lichen symbioses represent a major way of life among the Fungi. Almost one-fifth of all known fungal species are lichen-forming and within the Ascomycota about two-fifths of known species are lichenized. The morphological and physiological characteristics of these associations are highly specialized and often involve intricate connections between the symbionts. As lichens include primary as well as secondary producers, and have their own carbon cycles, they resemble miniature ecosystems rather than individuals or populations. The symbiotic nature of these systems is not limited to the thallus level biology of individual lichen species. Symbiotic processes also shape the structure of lichen communities on a global scale.