- Acidophilous – preferring acidic substrata or habitats
- Apothecia – disc shaped bodies which arise from the surface of the thallus and from which the fungal spores are produced.
- Association – communities characterised by floristic composition, constant and differential species; the basic unit of phytosociological classification equivalent to that of the 'species' in idiotaxonomy (q.v.); the first name of an association ends in the suffix -etum (for example, Parmelietum furfuraceae)
- Basiphilous – preferring base-rich substrata
- Calcicole – an inhabitant of a calcium-rich substratum
- Calciphilous – preferring substrata rich in calcium compounds
- Characteristic species, espèce caractéristique (Fr.), Charakterart (Germ.), ledart (Swed.) – species used in the delimitation of a community (phytosociological)
- Corticolous – growing on or inhabiting bark
- Crustose – forming a crust which is firmly attached to the substrate over its entire area.
- Endemic – occurring only in a single, usually small, geographic area
- Endolithic – of saxicolous lichens with at least their phycobiont living within the substratum
- Epilithic – of saxicolous lichens growing on the surface of substrata
- Epiphytic – growing non-parasitically on plants (usually woody)
- Epixylic – growing on wood surfaces
- Eutrophicated – nutrient-enriched (correctly used of water); cf Hypertrophicated
- Flora – (1) the plant kingdom; (2) the plants in a particular geographic region or site; (3) a list, usually annotated, of the plants in a particular geographic region or site
- Foliicolous – growing on leaves
- Foliose – flattened and leaf-like. Often attached over a large area but with at least the margins of the lobes free.
- Fruticose – shrubby and attached to the substrate by only one or a few points. Lacking a distinct upper and lower surface
- Habit – the morphological form assumed by an individual or species
- Habitat – a particular site with a specific set of conditions; natural place of occurrence of an organism; a loosely applied term
- Index of Ecological Continuity (IEC) – the percentage of 20 selected old-forest indicator species (q.v.) occurring in a particular site; Revised Index of Ecological Continuity (RIEC): the percentage occurrence of up to a maximum of 20 out of a total list of 30 selected old-forest indicator species; IEC and RIEC have proved valuable in assessing the relative importance of sites for lichen characteristic of little disturbed woodlands in the British Isles
- Index species – see Characteristic species
- Indicator species – a species whose presence or absence shows whether or not particular conditions prevail or prevailed at a site
- Isidia – tiny peg-like protruberances from the surface of the thallus. Since they include both fungal and algal cells, borken off isidia constitute an effective method of vegetative dispersal.
- Lacustrine – pertaining to lakes
- Lichenicolous – growing on lichens
- Lichenometry – measurement of lichen growth; specifically used as a technique for dating rock surfaces by the size of lichen thalli
- Lignicolous – growing on decorticate wood (lignum)
- Littoral – of the zone on rocky shores which is emersed (q.v.) and subemersed by the tide on sheltered shores, but may be continuously emersed on very exposed shores
- Mesic-supralittoral – wettest part of the supralittoral (q.v.), which is occasionally washing by splashing waves
- Mesotrophic – of a water-body that is intermediate between nutrient-poor (oligotrophic) and nutrient-rich (eutrophic)
- Metallophytes – species confined to substrata with very high heavy metal contents
- Microhabitat – a particular ecological niche within a more broadly defined habitat, for example, rock under hang, leaf surface or bark crevice
- Muscicolous – growing on or over mosses
- Neutrophilous – preferring basic or neutral surfaces
- Nitrophilous – preferring substrata rich in nitrogenous compounds
- Obligate – restricted to a particular host, substratum or method of nutrition; cf. Facultative
- Old-forest indicator species – species normally found only in mature or extremely old stands of forest or ancient parklands; used in calculation of Index of Ecological Continuity (q.v.)
- Oligotrophic – of a water-body that is poor in nutrients
- Perithecia – small, wart-like bodies partly immersed in the thallus and from which the fungal spores are produced.
- Pioneer – the first species or communities establishing themselves on a particular substratum
- Saxicolous – growing on or inhabiting rocks
- Siliceous – used of rocks with a high silicate content; often misused to imply non-basic or acidic
- Silicicolous – growing on siliceous rocks
- Submesic-supralittoral – seldom splashed zone above mesic-supralittoral (q.v.) dominated by Xanthoria parietina
- Substrate – the material or medium in or on which an organism grows (and from which it usually derives nutrients); used more widely as synonymous (perhaps incorrectly) with substratum (pl. substrata); specifically used a s a chemical term defining a medium or matrix
- Succession – the replacement of one community by another in the same site
- Supralittoral – zone on rocky shores never submerged by the tide but containing non-terrestrial lichens; it has three subzones; submesic-, mesic- and xeric-supralittoral
- Taxon (pl. taxa) – a taxonomic (idiotaxonomic) group of any rank; a neutral term; cf. Syntaxon
- Terrestrial – on or of the land or earth (used in a more limited sense to describe a zone of rocky sea-shores where species predominate which are also widespread in inland sites)
- Terricolous – growing on the ground or soil
- Xeric-supralittoral – zone of rocky shore receiving sea water only as wind-borne spray; drought prone part of the shore