Amyloid – if a lichen is amyloid (in the medulla), there is a blue / violet reaction after the addition of a drop of iodine.

Apothecium – fruiting body in many ascomycetes (and therefore most lichens, since 99 % of all lichens are ascomycetes).

Areole – a part of the thallus that contains both fungal tissue and algae cells (see picture). The outer layer is called the cortex (bark). The inner layer is called the medulla (marrow).

Ascospore – sexual spores in ascomycetes.

Ascus – spore-producing cell in hymenium.

C – calcium hypochlorite, used for spot tests to detect lichen acids.

Cortex – the outer layer of an areole, consisting only of fungal tissue. The algae are often located just below the cortex.

Crustose – a growth form, means that the lichen grows densely attached to a substrate, without undergrowth and attachment threads.

Epihymenium / epithecium – upper layer of hymenium. May contain pigments and / or crystals.

Excipulum – the outer layer of the apothecium.

Halo – gelatinous layer that surrounds ascospores in Rhizocarpon. Also called perispore.

Hymenium – the spore-producing cell layer in an apothecium. Consists of sterile paraphyses and fertile, spore-producing asci (singular: ascus).

Hypothallus – a sterile mat of fungal tissue that grows under the thallus, closest to the substrate. Important character for Rhizocarpon, because the areoles and fruiting bodies originate from the hypothallus, but is also found in many other crustose lichens.

Hypothecium – the layer under hymenium in an apothecium.

Iodine – used to detect amyloidity in lichen.

K – potassium hydroxide, 10 %, used for spot tests to detect lichen acids.

Medulla – the inner layer of an areole, below the cortex and algal layer.

Paraphysis – sterile protective / supportive cell threads in hymenium.

Pd – para-phenylenediamine, used for spot tests to detect lichen acids. Carcinogenic, use with caution!

Perispore – gelatinous layer that surrounds ascospores in i.e. Rhizocarpon. Also called halo.

Saxicolous – literally "rock dweller", which means that the lichen lives on rock substrates.

Septum – internal cell wall in a spore, important character in Rhizocarpon.

Thallus – the "body" of lichen, consists of fungal tissue and algae cells.

TLC – thin-layer chromatography, a method for detecting secondary metabolites in lichen.