This glossary provides an overview of terms used in the description of lichens, composite organisms arising from algae or cyanobacteria living symbiotically among filaments of multiple fungus species. [1] [2]
Erik Acharius, known as the "father of lichenology," coined many lichen terms still in use today around the turn of the 18th century. Before that, only a couple of lichen-specific terms had been proposed. Johann Dillenius introduced scyphus in 1742 to describe the cup-shaped structures associated with genus Cladonia , while in 1794 Michel Adanson used lirella for the furrowed fruitbodies of the genus Graphis . Acharius introduced numerous terms to describe lichen structures, including apothecium , cephalodium , cyphellae , podetium , proper margin , soredium , and thallus . In 1825, Friedrich Wallroth published the first of his multi-volume work Naturgeschichte der Flechten ("Natural History of Lichens"), in which he proposed an alternative terminology based largely on roots from the Greek language. His work, presented as an alternative to that of Acharius (of whom he was critical) was not well received, and the only terms he proposed to gain widespread acceptance were epi- and hypophloeodal , hetero- and homoiomerous , and gonidium , the last of which remained in use until the 1960s. [3] Until about 1850, there were 21 terms for features of the lichen thallus that remain in use today. [3]
The increasing availability of the optical microscope as an aid to identifying and characterizing lichens led to the creation of new terms to describe structures that were previously too small to be visualized. Contributions were made by Julius von Flotow (e.g. epithecium ), Edmond Tulasne (e.g pycnidium ), and William Nylander (e.g. pseudocyphella , thecium ). Gustav Wilhelm Körber, an early proponent of using spore structure as a character in lichen taxonomy, introduced amphithecium , muriform , and "polari-dyblastae", later anglicized to "polari-bilocular" and then shortened to polarilocular . [4] In the next five decades that followed, many other additions were made to the repertoire of lichen terms, subsequent to the increased understanding of lichen anatomy and physiology made possible by microscopy. For whatever reasons, there were not any new terms (still currently used) introduced from the period 1906 to 1945, when Gustaf Einar Du Rietz proposed replacing epi- and hypothecium with epi- and subhymenium ; all four terms remain in use. [4] In some cases, older terminology became obsolete as better understanding of the nature of the fungal–algal relationship led to changes in their terminology. For example, after Gunnar Degelius objected to the use of gonidia for the algal partner, George Scott proposed the use of mycobiont and phycobiont for lichen components, recommendations that were generally accepted by lichenologists. [5]
This glossary includes terms defining features of lichens unique to their composite nature, such as the major components the two major components of lichens ( mycobiont and photobiont ); specialized structures in lichen physiology; descriptors of types of lichens; two- and three-dimensional shapes used to describe spores and other lichen structures; terms of position and shape; prefixes and suffixes commonly used to form lichen terms; terminology used in methods for the chemical identification of lichens; the names of 22 standard insoluble lichen pigments and their associated reference species; and "everyday" words that have a specialized meaning in lichenology. The list also includes a few historical terms that have been supplanted or are now considered obsolete. Familiarity with these terms is helpful for understanding older literature in the field.
Psora is a genus of lichen-forming fungi in the family Psoraceae. Members of the genus are commonly called fishscale lichens. Lichens in the genus Psora generally have a squamulose thallus and anthraquinones in the hymenium. Photobiont partners of Psora lichens include members of the green algal genera Asterochloris, Chloroidium, Myrmecia, and Trebouxia.
An isidium is a vegetative reproductive structure present in some lichens. Isidia are outgrowths of the thallus surface, and are corticated, usually with a columnar structure, and consisting of both fungal hyphae and algal cells. They are fragile structures and may break off and be distributed by wind, animals, and splashing raindrops. In terms of structure, isidia may be described as warty, cylindrical, clavate (club-shaped), scale-like, coralloid (coral-shaped), simple, or branched.
Verrucariaceae is a family of lichens and a few non-lichenised fungi in the order Verrucariales. The lichens have a wide variety of thallus forms, from crustose (crust-like) to foliose (bushy) and squamulose (scaly). Most of them grow on land, some in freshwater and a few in the sea. Many are free-living but there are some species that are parasites on other lichens, while one marine species always lives together with a leafy green alga.
A plant lichen is a lichen with flat, leaf-like lobes, which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common growth forms of lichens. It typically has distinct upper and lower surfaces, each of which is usually covered with a cortex; some, however, lack a lower cortex. The photobiont layer lies just below the upper cortex. Where present, the lower cortex is usually dark, but occasionally white. Foliose lichens are attached to their substrate either by hyphae extending from the cortex or medulla, or by root-like structures called rhizines. The latter, which are found only in foliose lichens, come in a variety of shapes, the specifics of which can aid in species identification. Some foliose lichens attach only at a single stout peg called a holdfast, typically located near the lichen's centre. Lichens with this structure are called "umbilicate". In general, medium to large epiphytic foliose lichens are moderately sensitive to air pollution, while smaller or ground-dwelling foliose lichens are more tolerant. The term "foliose" derives from the Latin word foliosus, meaning "leafy".
Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their growth form. This form, which is based on the appearance of vegetative part of the lichen, varies depending on the species and the environmental conditions it faces. Those who study lichens (lichenologists) have described a dozen of these forms: areolate, byssoid, calicioid, cladoniform, crustose, filamentous, foliose, fruticose, gelatinous, leprose, placoidioid and squamulose. Traditionally, crustose (flat), foliose (leafy) and fruticose (shrubby) are considered to be the three main forms. In addition to these more formalised, traditional growth types, there are a handful of informal types named for their resemblance to the lichens of specific genera. These include alectorioid, catapyrenioid, cetrarioid, hypogymnioid, parmelioid and usneoid.
Lichen morphology describes the external appearance and structures of a lichen. These can vary considerably from species to species. Lichen growth forms are used to group lichens by "vegetative" thallus types, and forms of "non-vegetative" reproductive parts. Some lichen thalli have the aspect of leaves ; others cover the substrate like a crust, others such as the genus Ramalina adopt shrubby forms, and there are gelatinous lichens such as the genus Collema.
Ochrolechia africana, commonly known as the frosty saucer lichen, is a species of crustose and corticolous (bark-dwelling) lichen in the family Ochrolechiaceae. It is a widely distributed species, found in tropical and subtropical areas of southern Africa, Asia, Australia, North America, and South America. The lichen is characterized by the presence of a white "frosty" or powdery apothecia.
Clandestinotrema is a genus of lichen-forming fungi in the family Graphidaceae. It has 17 species. They typically inhabit montane and cloud forest at higher elevations in the tropics.
Pertusaria galapagoensis is a species of corticolous (bark-dwelling), crustose lichen in the family Pertusariaceae. Found on the Galápagos Islands, it was formally described as a new species in 2015 by Elix, Yánez-Ayabaca, A.W.Archer & Bungartz. The type specimen was collected on Floreana Island at an altitude of 371 m (1,217 ft), where it was found growing on the bark of a south-exposed trunk of Cedrella odorata. The species epithet refers to its distribution.
Ampliotrema sorediatum, a corticolous lichen, is a species in the family Graphidaceae. It was discovered in the tropical lowland rainforest of Peru. The species epithet sorediatum refers to the unusual sorediate thallus, which distinguishes this species from its closest relative, Ampliotrema lepadinoides. The lichen was described as a new species in 2008 by lichenologists Eimy Rivas Plata and Robert Lücking.
Compositrema cerebriforme is a species of corticolous (bark-dwelling) lichen in the family Graphidaceae. It is notable for its distinct structure and resemblance to the shape of a brain. It was discovered in the greenery of Venezuela's Henri Pittier National Park, and described as a new species in 2012.
Enterographa rotundata is a species of corticolous (bark-dwelling) crustose lichen in the family Roccellaceae. This species was discovered in Brazil, growing on the smooth bark of trees in the Brazilian Caatinga forest. It has round apothecia, a feature that sets it apart from most of its kind.
Gyalideopsis aptrootii is a species of corticolous lichen in the family Gomphillaceae. Found in southern Brazil, it was described as a new species in 2018. Defining features of this lichen include the unique crescent-shaped structure of its hyphophores, the single-spored asci, and the relatively small size of the ascospores.
Lempholemma polycarpum is a little-known species of saxicolous (rock-dwelling) lichen in the family Lichinaceae. It was first described from Yemen and is characterised by its blackish thallus, abundant small apothecia, and cyanobacteria from the genus Nostoc as its photobiont. The lichen is found on inclined limestone boulders in sun-exposed habitats with open forest vegetation. It also occurs in Madagascar and in Aldabra.
Gyrotrema papillatum is a little-known species of corticolous (bark-dwelling), crustose lichen in the family Harpidiaceae. It is known from a single collection in a lowland rainforest region of Costa Rica.
Megalospora austropacifica is a species of corticolous (bark-dwelling), crustose lichen in the family Megalosporaceae. It is found on the islands of Taveuni and Viti Levu in Fiji. It has a yellowish grey to whitish grey, glossy thallus that is thick and may appear slightly wrinkled or smooth, often with irregular cracks and small papillae containing conidiomata, but lacking isidia and soredia. Its apothecia are circular, up to 4.5 mm in diameter, with the disc evolving from concave to slightly convex and coloured from orange-brown to red-brown, surrounded by a thick, prominent margin.
Malmidea subcinerea is a species of corticolous (bark-dwelling), crustose lichen in the family Malmideaceae. It is found in Venezuela. The lichen has a smooth, dull thallus varying in colour from grey to olive, with a white internal medulla. It has sessile, rounded apothecia with light beige to greyish-brown discs.
Malmidea volcaniana is a species of corticolous (bark-dwelling), crustose lichen in the family Malmideaceae. It is found in Venezuela. A major characteristic of the species is the coralloid (coral-shaped) clumps of isidia-like outgrowths on the thallus surface.
Ocellularia vizcayensis is a rare species of corticolous (bark-dwelling) lichen in the family Graphidaceae. It is known from a single collection made in Luzon, Philippines. The lichen thallus is a white, irregularly structured, areolate surface with a layer that includes a photosynthetic partner, both containing large calcium oxalate crystals. Its fruiting bodies are either embedded or protruding, round, with very narrow openings, and contain large, oblong, colorless spores that turn violet-blue when stained with iodine.
Glaucomaria carpinea is a species of corticolous (bark-dwelling), crustose lichen in the family Lecanoraceae. It is a widely distributed species.