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Lichen glossary

Apothecium

A disc or cup-shaped fruiting body involved in sexual reproduction in lichens. It produces fungal spores. They are used in the identification of lichens. Apothecium, singular; Apothecia, plural. In conversation lichenologists often refer to them as ‘the apts’.

Areole

The thalli of some lichens are divided up by cracks to give a dried mud appearance. These islands of the thallus are termed areoles. They are frequently used in lichen identification.

Ascospore

A spore formed in the ascus within the apothecia.

Ascus

The sac or bag-like structure in the apothecium that holds spores. It is indicative of the Phylum Ascomycota in the Fungi.

Concolorous

Means ‘the same colour’. It is a term frequently used in the description of lichens.

Conidium

An asexual fungal spore. Conidia, plural.

Cortex

The outermost layers of a thallus. It consists of tightly woven fungal hyphae. It is sometimes used in chemical tests to verify lichen identification.

Corticolous

A term used to describe lichens that grow on bark.

Crustose

A type of lichen body in which it is impossible to remove the lichen from its substrate without damaging it significantly. This classification is used in the identification of lichens.

Cyanobacterium

A bacterium that can photosynthesise, consequently producing sugars. The old term for these bacteria was blue-green algae. It is recommended that the old term is not used.

Cyphella

A tiny depression on the lower surface of the lichen thallus that holds spherical cells. It is indicative of the genus Sticta.

Diploid

When chromosomes appear in working pairs (one from each parent), the cell containing them is said to be in the diploid state. See haploid also.

Disc

This refers to the surface of the apothecia. The disc can be various colours and be flat, convex or concave. These characteristics are used in the identification of a lichen.

Foliose

A lichen body shape which is leaf-like with a distinct upper and lower surface. Foliose lichens are usually easily separated from the substrate.

Fruiting body

A term used to describe the sexual reproductive parts of a lichen such as the apothecia or perithecia.

Granular

A term used to describe the thallus which has a sugar-like appearance due to the presence of soredia. Soredia may be used to identify a lichen.

Haploid

When chromosomes in a cell are unpaired (as an unpaired shoe), the cell is said to be in the haploid state. The unpaired chromosome is from either the ‘father’ or ‘mother’.

Hyphae

A filament of cells or nuclei in a tube. They make up the bulk of the body of fungi and lichens.

Isidium

A tiny finger-like growth on the surface of a thallus. It is an asexual reproductive structure that contains photobiont and fungal cells surrounded by cortex cells. Isidia, plural.

Leprose

A term used to describe a thallus that is wholly made up of soredia.

Lichenicolous

Means ‘growing on lichens’.

Medulla

The loosely woven central internal section of a thallus that is home to photobiont cells.

Mycobiont

The fungal part of a lichen.

Perithecium

A sexual reproductive structure that produces spores (like the apothecium) and is often buried in the thallus of the lichen although it can be prominently visible at the thallus surface. It opens to the surface through a tiny pore. These pores look like dots on the thallus and are frequently used as an identification aid.

Photobiont

The photosynthesising partner in a lichen. It can be algae or a cyanobacteria.

Podetium

A stalk found in the group Cladonia. It is hollow and holds the fruiting bodies at the tip.

Propagule

A general term for a structure involved in the dispersal of sexual or asexual reproductive parts.

Pruinia

A fine (usually white) powder often seen on the discs of apothecia or on the surface of the thallus. It is often used in lichen identification.

Pseudocyphella, pl. pseudocyphellae

A circular or elongated depression in the cortex (upper or lower) that opens into the light coloured medulla. It is seen under a hand lens as dots or lines and is frequently used to aid in lichen identification.

Pycnidium

A flask-shaped structure embedded in the thallus that opens to the outside through a pore. It produces conidia.

Rhizine

A root-like structure made from a single hyphal filament that grows from the underside of the thallus. It functions to hold the lichen to the substrate and to absorb nutrients.

Saxicolous

A term used to describe lichens that grow on rocks.

Siliceous

A rock rich in the mineral silica. It includes granite, quartzite, gneiss, basalt and rhyolite. The term ‘acid’ is often used to describe these rocks, but the term siliceous is to be preferred.

Soralium

A closely arranged group of soredia. Soralia, plural. An important descriptive term in the identification of lichens.

Soredium

A tiny growth (often spherical) of hyphae that holds a few algal cells. It is dispersed by the lichen as a method of vegetative reproduction.

Spore

A sexual reproductive cell produced by the fungal partner of the lichen.

Squamule

A small leaf-like or scale-like structure typically found in the Cladonia group. It lacks rhizines.

Symbiosis

A relationship between two organisms that is usually long term with the following two possibilities: (i) both partners in the symbiosis benefit (mutualistic symbiotic relationship) or (ii) just one partner will benefit at the expense of the other (parasitic symbiotic relationship).

Terricolous

Describes lichens that grow on soil.

Thalline margin

Describes the margin of an apothecium that is continuous with the thallus and is usually the same colour as the thallus.

Thallus

The main vegetative body of the lichen. It is composed of fungal hyphae and a photobiont (algae or cyanobacteria).

Trebouxia

A common green algae found in lichens.

Trentepohlia

A filamentous green algae found as the photobiont in some lichen species. It is often seen growing on bark without its fungal partner (especially on birch) and looks orange in colour.

UV Test

A test to help identify lichens in which ultra violet light is used to show the presence/absence of specific lichen substances.