soredium

A soredium (plural soredia) is a vegetative propagule used by many lichens to reproduce asexually. It consists of algal or cyanobacterial photobiont cells surrounded by fungal hyphae from the lichen’s mycobiont, forming a small, often powdery or granular mass on the thallus surface.

Structure and composition: Soredia are typically clusters of photobiont cells enveloped by a network of fungal hyphae, sometimes with only a few hyphae linking the algal cells. They generally lack a protective cortex, making them more readily detached and dispersed than some other propagules. Soredia can appear as discrete granules or as a diffuse, powdery coating on the lichen surface.

Formation and dispersal: Soredia develop on the thallus and are shed or blown away by wind, rain, or contact. When deposited on a suitable substrate, the embedded photobiont and mycobiont can regenerate a new thallus, provided the symbiotic partnership re-establishes successfully. Soredia enable rapid local and, over time, wider colonization in favorable climates.

Distinctions and context: Soredia are one mode of vegetative reproduction in lichens; another common form is isidia, which are elongated outgrowths that contain fungal and algal tissue and often possess a cortex. In contrast to sexual reproduction, which yields genetically diverse offspring, soredia produce clones of the parent lichen. Soredia are widespread among crustose and foliose lichens and contribute to their persistence in variable environments.