Isidium
An isidium is a small, corticated outgrowth of a lichen thallus that can detach and propagate the lichen vegetatively.
Lichen: A stable association between a fungus and a photosynthetic partner, usually an alga or cyanobacterium. An isidium is a vegetative propagule produced by a lichen thallus.
Fungal hypha: A branching filament of cells that forms the structural body of most fungi. Hyphae make up the fungal tissue surrounding photobiont cells in an isidium.
Lichen identification: The determination of a lichen's taxonomic identity using its form, chemistry, and habitat. Isidial presence, shape, and distribution are useful diagnostic characters.
Lichen conidium: An asexual fungal spore produced by a lichen-forming fungus, generally lacking the photobiont. Unlike an isidium, a conidium usually disperses fungal material without its photosynthetic partner.
Soredium: A powdery lichen propagule consisting of fungal hyphae and algal or cyanobacterial cells, usually without a cortex. Soredia also disperse both partners, but lack the organized outer cortex characteristic of isidia.
Alga: A diverse group of mostly aquatic, photosynthetic organisms that lack the embryos of land plants. Many lichen photobionts are green algae carried within isidia.
Lichen dispersal: The movement of lichen propagules to sites where new thalli can establish. Detached isidia provide one means of local vegetative dispersal.
Lichen ascospore: A sexual spore formed in the ascus of a lichen-forming fungus. An ascospore must encounter a suitable photobiont, whereas an isidium carries one.
Lichen thallus: The body of a lichen, formed by fungal tissue associated with a photosynthetic partner. Isidia arise as outgrowths from this body.
Cyanobacteria: Photosynthetic bacteria that produce oxygen and often occur as partners in lichens. Some isidia carry cyanobacterial photobionts instead of, or alongside, green algae.