The following is a

glossary A glossary (from grc, γλῶσσα, ''glossa''; language, speech, wording) also known as a vocabulary or clavis, is an alphabetical list of Term (language), terms in a particular domain of knowledge with the definitions for those terms. Tradi ...

of terms used in the description of

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.organisms that arise from

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

living among filaments of multiple fungus species in a mutualistic relationship. Erik Acharius

Until the end of the 18th century, only a couple of lichen-specific terms had been proposed. Johann Dillenius introduced ' in 1742 to describe the cup-shaped structures associated with genus '' Cladonia'', while in 1794 Michel Adanson used ' for the furrowed fruitbodies of the genus '' Graphis''. Erik Acharius, the "father of lichenology", conceived many new terms to describe lichen structures in several of his seminal publications in the early 1800s. Examples include , , , , , , and . 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 A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...

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 and , and , and , the last of which remained in use until the 1960s. Until about 1850, there were 21 terms for features of the lichen thallus that remain in use today. 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 Julius von Flotow; full name- Julius Christian Gottlieb Ulrich Gustav Georg Adam Ernst Friedrich von Flotow (9 March 1788 – 15 August 1856) was a German military officer and a botanist specialized in lichenology and bryology. Von Flotow was bor ...

(e.g. ),

Edmond Tulasne Louis René Étienne Tulasne, a.k.a. Edmond Tulasne (12 September 1815 – 22 December 1885) was a French botanist and mycologist born in Azay-le-Rideau. He originally studied law at Poitiers, but his interest later turned to botany. As a yo ...

(e.g ), and William Nylander (e.g. , ). Gustav Wilhelm Körber, an early proponent of using spore structure as a in lichen taxonomy, introduced , , and "polari-dyblastae", later anglicized to "polari-bilocular" and then shortened to . 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 and with and ; all four terms remain in use. 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 for the algal partner, George Scott proposed the use of and for lichen components, recommendations that were generally accepted by lichenologists. Terms defining features of lichens are used to describe aspects and relationships unique to lichens as composite organisms. These include terms that describe the two major components of lichens (' and '); specialized structures in lichen physiology (e.g., podetium, , medulla, the ); descriptors of types of lichens (e.g., , , ); two- and three-dimensional shapes used to describe spores and other lichen structures (e.g., , , ); terms of position (e.g. , ) and shape (e.g. , );

prefix A prefix is an affix which is placed before the Word stem, stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates the word ''unhappy'' ...

es and

suffix In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns, adjectives, and verb endings, which form the conjugation of verbs. Suffixes can carry ...

es commonly used to form lichen terms; terminology used in methods for the chemical identification of lichens (e.g. various spot tests); and "everyday" words that have a specialized meaning in lichenology (e.g., , , ). The list also includes a few historical terms that have been supplanted or are now considered obsolete (e.g., , ). Although no longer part of the modern lichen lexicon, knowledge of these terms helps in understanding older literature.