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.
Referring to a developmental process in lichens where certain structures, such as spores or reproductive organs, fail to reach full development or maturity, often resulting in non-viable or malformed structures.7
A lichen product that is sometimes present, sometimes not present in a species. In literature, these are usually indicated with a ± symbol, e.g. ±usnic acid.9
Referring to fruticose lichens, a branching pattern that is unusual or abnormal, like that which sometimes occurs after the original branches are damaged in Cladonia.8
-al
A suffix used to indicate a relation to, or having the form and character of something.20
Plural alcobioses. A form of symbiosis involving algae and corticioid fungi, primarily occurring on bark and wood surfaces. In this relationship, algae form a layer beneath the fungal basidiomata—structures akin to the photobiont layer in lichens. This association, unlike in lichens, does not render the fungal partner nutritionally dependent on the algae, thus all involved fungal species are capable of surviving without the algal partner. Alcobiosis represents a diverse interaction, seen in various stages of coevolution, involving multiple species across the Agaricomycetes fungal group and three algal species from the class Trebouxiophyceae.24
alveolate
Used to describe a surface that has a pattern similar to a honeycomb (i.e. with more or less 6-sided hollows), where the surface appears to be composed of small pits or cavities like alveoli.25Compare: faveolate, foveolate, scrobiculate.
amphi-
A prefix used to indicate on both sides, or on all sides.26
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Ampliotremoid lichens have
prominent apothecia with wide pores, black walls (viewed in microscopic section), and a smooth, more or less shiny thallus; this morphotype occurs in the genera Ampliotrema and Ocellularia.30
ampulliform
Bottle-shaped, i.e., with a narrow neck and swollen base.31
Also anisotomous.33 Having branches of unequal length;34 if the branching is anisotomic, one branch is typically stouter than the other, forming a main stem while the other appears like a lateral branch, as in the species Alectoria ochroleuca.33Contrast: dichotomous.
annulotremoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Annulotremoid lichens have prominent apothecia with wide pores, pores with an inner ring, and a smooth, more or less shiny thallus; this morphotype occurs in the genera Myriotrema and Thelotrema.30
anticlinal
Perpendicular to a surface;35 used to refer to hyphal alignment.
apical
Located at the highest point (the apex), the tip, or the end of something.36
apiculate
Having a short projection (an apicule) at one end; typically used to describe spore morphology.37
apothecium
Plural apothecia. A type of ascocarp that is open, saucer-shaped or cup-shaped, and in which the hymenium is exposed at maturity.38 The term was first used by Erik Acharius in 1803.3
Also arachnoidal, araneose, araneous.40 Having a cobweb-like form, like that of the irregularly oriented and loosely interwoven hyphae of the medullary layer of some lichens.41
Arceutina-yellow
A pale yellow insoluble lichen pigment, associated with the reference species Bacidia arceutina.42
arcuate
A shape or structure that is curved or arched like a bow.43
ardella
Plural ardellae. A type of apothecium, typical of lichens in the family Arthoniaceae, which is small and round. Elongated ardellae are called lirellae.44 The term was first used by William Allport Leighton in 1854, who described an ardella as resembling a "sprinkled spot".4
Plural areoles. Also areola with plural areolae. A small area, typically rounded to polygonal or irregular in shape, and often with a distinct texture. In a lichen thallus, the areolae are often separated from the rest of the thallus by fissures or cracks.45
areolate
Also areolar. The condition of being made of or covered with areolae, such as the areolate lichens.45
Arnoldiana-brown
A reddish-brown insoluble lichen pigment, associated with the reference species Bacidina arnoldiana.46
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. This term refers to a morphotype of lichen where the apothecia are partially embedded and partially protruding, having a dark, hardened thalline margin that forms irregular cracks. This morphotype is uniquely seen in "Thelotrema" dislaceratum, a species with uncertain taxonomic placement.58
Also bacilliform, baculate, baculiform. Shaped like a small rod, typically with a length:width ratio of about 3:1.59
Bagliettoana-brown
A pale to brownish-green insoluble lichen pigment, associated with the reference species Bacidia bagliettoana.60
basidiolichen
A lichen in which the fungal partner (the mycobiont) is a member of the Basidiomycota. About 0.4% of lichens are basidiolichens.51See related: ascolichen.
Referring to a type of ascus in which the ectotunica splits at the top and exposes the endotunica by forming an opening with a lip on each side; bilabiate asci occur in the genus Pertusaria.63
Also defined: endotunica, ectotunica. A type of ascus that has two functional layers, the internal layer, the endotunica, and the external layer, the ectotunica. Bitunicate asci are characteristic of the historical class Loculoascomycetes.67
A symbiotic interaction where either green algae or cyanobacteria are enveloped by fungal tissue, but without forming the discrete layers that occur in most lichens.70
botryose
Resembling rounded, bead-like structures or clusters resembling grapes.43
A lateral growth of the main stem of a thallus in usneoid lichens; various features of a branch are diagnostically valuable in distinguishing species.71
Also defined: hepaticolous lichen; muscicolous lichen. A lichen that grows on a moss or liverwort – i.e. on a bryophyte.73 A hepaticolous lichen is found only on liverworts, while a muscicolous lichen is found only on mosses.7475
bullate
Having blister-like or bubble-like swellings on a surface.76
Also caespitous, cespitose.79 Growing in dense clusters or tufts, often used to describe fungi that arise from a common base or grow closely together without fusing.18
A lichen that prefers acidic soils and tends to avoid, or is intolerant of, alkaline conditions often associated with high calcium carbonate content; opposite of calcicole.81
Having one or more longitudinal grooves or channels.83
capitate
Having a well-formed head, usually spherical or hemispherical in shape.68See related: fuscocapitate.
capitulum
Plural capitula;also sphaeridium/sphaeridia. A more-or-less spherical or cup-shaped apothecium on the top of a stalk, found in the genera Calicium and Chaenotheca.8468See related: mazaedium.
carbonized
Also carbonised, carbonaceous. Blackened and brittle tissue resulting from the accumulation of pigments.85
cariose
A lichen thallus or structure that is cracked, split, spongy, or otherwise decayed or in a state of disintegration.43
cartilaginous
Also (in taxonomic names) cartilagineus. A term used to describe the texture of certain parts of a lichen. Cartilaginous structures have a texture similar to animal cartilage – firm but somewhat pliable, not brittle or soft.86
Plural cavernulae. A small hollow or cavity; used to refer to the holes in the lower cortex of the genus Cavernularia.90
central axis
Also chondroid axis. The cartilage-like central core in the branches of usneoid lichens, made of longitudinally arranged hyphae.71 The term "chondroid axis" was first used by William Nylander in 1858.4
cephalodium
Plural cephalodia. A small gall-like structure that contains cyanobacteria, found in some lichens. These structures can be located on the lichen's upper or lower surface, or within the thallus itself.68 These structures are found in most lichens that contain both algal and cyanobacterial photobionts.91 The term was first used by Erik Acharius in 1803.3
cerebriform
Having a surface texture that is deeply wrinkled or convoluted in a manner resembling the structure of a brain. The term is used to characterize the appearance of certain lichens with a complex, highly folded thallus.92
cetrarioid lichen
An informal growth form category used for lichens with erect, foliosethalli, and apothecia and pycnidia on the margins of the lobes; characteristic of lichens previously classified in the genus Cetraria (in the broad sense).93
chalaroplectenchyma
Plural chalaroplectenchymata. A type of plectenchyma comprising loosely interwoven hyphae with holes; found in the medulla of some lichens.92
character
A distinguishing feature that is characteristic for an organism; equivalent to phenotypic trait.92
chasmoendolith
Also chasmoendolithic. A type of organism, typically a lichen or fungus, that lives within cracks and fissures of rocks.94See related: endolith.
checklist
A list of all of the species (sometimes including subspecies, varieties and forms) that occur within a particular region.95
chemosyndrome
A set of lichen products produced by a species; this typically includes one or more major compounds and a set of biosynthetically related minor compounds.96
chemotype
Chemically differing types of a species with the same morphological characteristics, of no or unknown taxonomic significance.9
A lichen containing green algae (Chlorophyta) as its primary photobiont. The term serves as a counterpart to "cyanolichen" (lichens with cyanobacterial photobionts) and is preferred over the historically ambiguous term "phycolichen". It refers to the vast majority of eukaryotic lichen photobionts which belong to the division Chlorophyta.98
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. Chroodiscoid lichens have open apothecia with recurved lobules and a smooth and more or less shiny thallus; this morphotype occurs in the genera Acanthotrema and Chapsa.30
A green to turquoise insoluble lichen pigment, associated with the reference species Schaereria cinereorufa.100
citriform
A shape or form that resembles a lemon or citrus fruit. The term is used to describe structures, particularly ascospores or other components of a lichen, that have an elongated, oval shape with tapered ends.101
CK test
A seldom-used spot test performed with an application of C followed immediately by K.102
cladoniiform lichen
Also cladoniform lichen, dimorphic lichen.Also defined: primary thallus and secondary thallus. A lichen with a two-fold growth form that includes both a crustose, squamulose, or foliose form and a fruticose form; the thallus differentiates into both horizontal (primary thallus) and vertical (secondary thallus, or podetium) structures. Cladoniiform lichens occur in the families Cladoniaceae and Baeomycetaceae.103
clavate
Also claviform. A shape resembling a club, broader at one end and tapering towards the other; typically used to refer to ascospores and asci.104
In some Leptogium lichens, a ring at the apex of the apothecium made up of one, occasionally up to three, continuous lamellar folds encircling the disk; these folds may arise from laterally fused lobules and are distinct from separate, true lobules.107
colloplectenchyma
A type of apothecial tissue made up of slightly rounded cells with somewhat thickened walls, resembling the angular collenchyma of vascular plants; distinguished from paraplectenchyma, which consists of thin-walled, parenchyma-like cells.108
columella
A sterile, central column of tissue that extends upward within some lichen fruiting bodies (such as mazaedia or perithecia), typically from the base toward or to the apex.109
Having a finely scalloped edge; similar to crenate but with smaller notches.123
cruentodiscoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Cruentodiscoid lichens have open apothecia with erect lobules and a pigmented disc, and a smooth, more or less shiny thallus; this morphotype occurs in the genus Chapsa.30
crustose
A form of growth where the lichen is pressed so tightly against the substrate upon which it grows that it is impossible to remove without destroying either it or part of the substrate. Crustose lichens have a cortex only on their upper surface.124
cryptoendolith
Also cryptoendolithic. A type of organism, particularly certain lichens and fungi, that live inside rocks or in the microscopic spaces within the mineral grains of rocks.94See related: endolith.
Plural cyphellae. A sharply defined, rounded, ovate, or shapeless pore in the lower thallus surface (typically the lower cortex), which is lined with a "pseudocortex" made of loosely connected, non-gelatinized hyphae (often with globular cells, formed from the medulla) and bounded by a pale ring; known to occur in the genera Sticta and Oropogon.133 The term was first used by Erik Acharius in 1799.3
Having small tooth-like projections or serrations along the edge.138
dextrinoid
A chemical property referring to a substance's ability to turn reddish-brown in the presence of Melzer's reagent or iodine due to the presence of dextrins. This color reaction is also called hemiamyloid or pseudoamyloid.139
determinate
Having well-defined or clearly marked edges.140Contrast: effuse.
diagnosis
A brief account of a taxon describing the essential characteristics that distinguish it from its relatives.141
diahypha
Plural diahyphae. A type of conidium formed from hyphae that split apically in several branches, with prominent constrictions at the septa, resulting in the appearance of chain links; found in the family Gomphillaceae.142143
Also: disciform. A shape that is flat and circular, resembling a disk. In lichenology, this term often refers to the apothecia of lichens that have a flat, disk-like shape.147
discolichen
A grouping of ascolichens that produce disk-like apothecia, somewhat analogous to the fungal Discomycetes; the term applies to the majority of lichens.148
discothecium
Plural discothecia. The fruiting body of certain types of lichens, with cylindrical, bitunicate asci. It is distinguished from a hysterothecium, which is another type of fruiting body, by not opening through a slit but by expanding the asci to weather or push apart the typically thin upper stromatal layer.149 The term was introduced by Richard P. Korf in 1962.150
disk
Also: disc. The curved or flat upper surface of the hymenium in an apothecium, often pigmented and surrounded by a margin or rim.147
distal
Positioned away from a point of origin or from the center of a body.151
distoseptum
Plural distosepta. A type of septum found in some conidia and ascospores, which is located within but distinct from the outer wall and surrounds the internal lumina. Structures with distosepta are said to be distoseptate.152
Referring to crustose, areolate lichens with marginal areoles that are extended and arranged radially;158 also defined more generally as "obscurely lobed".159160
Also endolithic. A crustose lichen that grows in the interior of rocks (under and around the rock crystals), typically with little or no visible thallus on the outer rock surface.170Contrast: epilithic.See related: chasmoendolith, cryptoendolith, euendolith.
endophloeodal
Also endophloeodic, endophloeic, endophloic. Refers to crustose lichens whose thalli are more or less immersed in tree bark.171Contrast: epiphloedal.
Refers to margins or edges of lichen structures (such as apothecia, lobes, or thalli) that are smooth and unbroken, without any notches, teeth, or irregularities.172
epi-
Also ep-. A prefix meaning "upon" or "above".173174
epibryophyllous
Also epibryophytic. Referring to organisms, particularly lichens or fungi, that grow on the surface of mosses (bryophytes).173
A thin tissue layer of interwoven hyphae situated directly above the hymenium, which can contain pigments and sometimes plays a role in the coloration of the lichen.175Compare: epithecium.
epilithic
Also petricolous, rupicolous, saxicolous. A crustose lichen that grows on the surface of rocks.170Contrast: endolithic.
Also perrumpent. Breaking through a surface.182 A more precise definition has been suggested by Aptroot and Lücking, who propose that the term applies to ascomata and pseudostromata that are more than 1/2 to 3/4 above the level of the thallus.183
Plural eucortices or eucortexes. A cortex made of well-differentiated tissue.185 Another sense of the term, used by Josef Poelt, refers to cortical tissue made entirely of fungal cells originating from a cambium-like tissue layer in or above the algal layer.186 The term eucortex was first used by Gunnar Degelius in 1954.5
euendolith
Also euendolithic. A type of organism, often a lichen or microbe, that actively bores into and resides within the mineral matrix of rocks or other hard substrates.94See related: endolithic.
A sample page from Ludwig Schaerer's exsiccata series Lichenes Helvetici (Swiss lichens), published in 26 fascicles from 1823 to 1852. source ↗
exsiccatum
Plurals: exsiccata (from exsiccatum), exsiccatae (from exsiccata when used as singular for a collection), exsiccati (from exsiccatus). A dried and labeled herbarium specimen, often part of a numbered set.187
excipulum
Plural excipula.Alsoexciple (plural exciples). The cup-shaped or ring-shaped layer of tissue supporting the hymenium in an apothecium; this tissue sometimes develops into a distinct margin, as in the lecanorine apothecia.188See related: proper margin, thallin margin.
A region of the cortex where the hyphae are aligned perpendicularly to the main axis of the thallus.194 The term was first used by Auguste-Marie Hue in 1906.5See related: palisade cell.
Delicately fimbriate; bordered with minute fringe.201
fissitunicate
A form of bitunicate ascus in which the flexible layers of the inner wall (the endotunica) and the more rigid layers of the outer wall (the ectotunica) are physically separated; as a consequence, the inner walls extend past the outer walls before the spores are released.202
fissurine
Also fissurate. A term used characterize a structure or surface displaying a pattern of narrow, elongated cracks or fissures.203
fissurinoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. This morphotype is somewhat similar to the chroodiscoid, but it differentiates by the way the apothecia open through irregular thallus cracks, finally resembling chroodiscoid apothecia. It often has a unique elongated form at maturity and can be seen in species such as Acanthotrema brasilianum and various Chapsa species.204
Leaf-like; a type of lichen thallus comprising numerous small leafy lobes, often extending in a roughly circular pattern from a center of growth, on a lower cortex that is attached to the substrate by rhizines or at a base.209210
forage lichen
Lichens that serve as important food sources for fauna. For example, species from the genera Alectoria, Bryoria, and Cladonia are winter forage lichens for caribou in northern North America.211212
The outer gelatinous layer, also known as the g-layer, found on the exterior of an ascus, often exhibiting a gelatinous consistency and staining blue in iodine. Typically present in all asci, the fuzzy coat usually forms a thin layer along the ascus sides but may also appear as an apically thickened cap.220221
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Glaucescentoid lichens have open apothecia with erect lobules, and a rough thallus containing crystals; this morphotype occurs in the species Leucodecton glaucescens.30
glaucophaenoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Glaucophaenoid lichens have prominent apothecia with wide pores, pale walls (viewed in microscopic section), and a smooth and more or less shiny thallus; this morphotype occurs in the genus Myriotrema.30
A now-obsolete, historical term for the algal layer in a lichen.229
gonidium
Plural gonidia. A now-obsolete, historical term for a lichen photobiont.229 The term was first used by Friedrich Wallroth in 1825, and supplanted in the 1960s.3
gonimium
Plural gonimia. A now-obsolete, historical term for a lichen cyanobiont.229
A term for the general appearance (the habit) of a lichen.231
grumose
Having a granular or crumbly texture or appearance.43
guttulate
Referring to structures containing small oil droplets (guttules); often used to describe spores. More precisely, spores can be described as uni-, bi-, tri-, or multiguttulate.232
Also gyrate. Curved backward and forward; with folds and undulations.234
gyrotremoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Gyrotremoid lichens have open apothecia with recurved lobules, a disc that is pigmented with concentric rings, and a smooth, more or less shiny thallus; this morphotype occurs in the genus Gyrotrema.30
H
hafter
A flattened attachment point formed through direct contact of a lichen thallus to its substrate; associated with foliose and fruticose lichens that lack other attachment organs, such as Hypogymnia.235
halonate
Also defined: halo. Referring to a spore that is surrounded by a transparent outer layer or a gelatinous, translucent sheath. This sheath is readily observed when the spore is stained with India ink, as the ink does not penetrate the mucilage of the sheath, creating a light-transparent halo that is visible against a blackened background.236237
A green to turquoise insoluble lichen pigment, associated with the reference species Biatora hertelii.57
hetero-
Also heter-. A prefix meaning "other" or "different".239
heterocyst
A specialized type of cell found in some cyanobacteria; heterocysts are thought to be involved in the fixation of nitrogen by the lichen thallus, as well as in the multiplication of cyanobacteria.240
heteromerous
A lichen thallus that is organized into discrete layers or strata; the term applies to the majority of foliose, squamulose, and crustose lichens.241
Also hormocyte. Also defined: hormocystangium, plural hormocystangia. An asexual propagule, produced in a cup-shaped structure called the hormocystangium, comprising heavy, gelatinous fungal hyphae enclosing a few cyanobiont cells; these structures occur in some gelatinous lichens in the family Collemataceae.246 Both terms, hormocyst and hormocystangium, were introduced by Gunnar Degelius in 1945.5 According to one source, hormocyte and hormocytangium (spelled without the "s") are more accurate terms, because the cells (indicated by the ending -cyte) are not sexual propagules (which is implied by the ending -cyst).247
Plural hypothecia. A layer of tissue under the subhymenium in an apothecium; also used to refer more generally to all tissues under the hymenium.255 The term was first used by Carl von Martius in 1828.4
Embedded or sunken into the surface; in lichens, often used to describe perithecia.257 A more precise definition has been suggested by Aptroot and Lücking, who propose that the term applies to ascomata and pseudostromata that are more than 3/4 beneath the level of the thallus.183
incertae sedis
A term used for a taxon of uncertain, doubtful, or unknown classification.258
incised
Having deep, sharp notches or cuts along the edges, often describing the margins of a lichen's thallus or apothecia.164
Also defined: inspersion.Also inspers, interspersed. Terms used to describe the presence of minute, scattered oil droplets or granules within a tissue, typically observed in section with a compound microscope.260 An inspersion refers to the degree of obstruction caused by the sprinkling of small particles within different sections of a given structure.261
A structure that resembles an isidium, but is formed as an outgrowth of the medulla rather than the cortex; associated with soralia of species in the genus Usnea.265
isidiotremoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Isidiotremoid lichens lack apothecia and have isidia, and a smooth, more or less shiny thallus; this morphotype occurs in the genera Myriotrema and Ocellularia.30
isidium
Plural isidia. A propagule that is an outgrowth of the thallus; it has a cortex and contains photobiont cells.264 The term was first used in the sense it is used now by Georg Meyer in 1825, and adopted by Elias Fries in 1831.3
isodiametric
Having roughly equal dimensions in all directions, resulting in a roughly spherical or cube-like shape; often used to describe cells that are not elongated or flattened but maintain a uniform size across their width, height, and depth.266
Plural isthmuses or isthmi. The narrow middle portion between the two locules of a polarilocular spore.268
J
juga
Plural jugae. A tiny carbonized structure made of hyphal tissue, visible as a black dot, line, or ridge, on or in a thallus; associated with the genus Verrucaria.269
Also laciniated. Referring to an edge divided into delicate bands or narrow lobes.273
lactophenol cotton blue
Also LCB. A histologicalstain commonly used to prepare semi-permanent slides. With this reagent, fungal hyphae stain blue, and algal cells stain deep blue to blue-green.102
lacunose
Also lacunar, lacunous. A texture that appears pitted or containing gaps or holes, giving it a somewhat rough or uneven appearance.274
lageniform
Flask-shaped; with a swollen base tapering to a narrow top.275
lamella
Plural lamellae. In the genus Umbilicaria, lamellae are flattened plate- or strap-like structures that project downward from the thallus undersurface.276
lamelloid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. In this, apothecia are noticeably protruding and organized into several distinct, concentric rows of lobulateexcipula. This morphotype is seen in species like Chapsa lamellifera.277
laminal
All over the thallus surface, rather than in the center or on the margins.259Contrast: marginal.
Comparison of the lecideine apothecia of Lecidea fuscoatra (left) and the lecanorine apothecia of Lecanora allophana (right)
Diagrammatic representation and comparison of cross sections of lecideine (left) and lecanorine (right) apothecia source ↗
Laurocerasi-brown
A reddish- or purplish-brown insoluble lichen pigment, associated with the reference species Bacidia laurocerasi.56
lax
Loose, loosely woven, not compact; like the hyphae in the medulla.278
lecanorine
Also lecanoroid. An apothecium in which the disk is surrounded by a pale thalline margin, which has both algal and fungal cells, as in the genus Lecanora. The term is also used more generally to refer to crustose lichens of the order Lecanorales that have rounded apothecia with thick, protruding margins.279
lecideine
Also lecideoid. An apothecium in which the disk lacks a thalline margin, as in the genus Lecidea. The term is also used more generally to refer to apothecia with a blackened (carbonaeous) ring and a blackish disk.280
leiodisk
Also leiodisc. A disk of an apothecium that is smooth and without folds or protrusions.281 The term was introduced by George Llano in 1950.5
lepadinoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. This morphotype describes lichens where apothecia are semi-embedded to prominently protruding and have a free excipulum and a distinctive double margin. The thalline margin bulges and remains whole, while the excipulum is prominent and wavy-lobed. Fibrillithecis halei, Leucodecton occultum, Myriotrema costaricense, and Thelotrema are examples of this morphotype.282
leprocarpoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Leprocarpoid lichens have open apothecia with erect lobules and a mealy and more or less matte thallus; this morphotype occurs in the genus Chapsa.30
A dark red-brown insoluble lichen pigment, associated with the reference species Buellia leptocline.56
Leptoclinoides-brown
A brown insoluble lichen pigment, associated with the reference species Hafellia leptoclinoides.56
leptotremoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Leptotremoid lichens have immersed apothecia with small pores, and a rough thallus containing crystals; this morphotype occurs in the genus Leptotrema.30
leucodectonoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Leucodectonoid lichens have closed apothecia with tiny pores, and a rough thallus containing crystals; this morphotype occurs in the genus Leucodecton.30
The name of a historical class that contained all of the lichen-forming fungi. This name was used when it was still erroneously believed that these fungi were quite separate from the non lichen-forming fungi; now obsolete.284
Plural lirellae.Also hysterothecia, lirelline apothecia. A linear ascocarp, which may be straight, curved, branched, or flexuous, with a longitudinal slit; characteristic of lichens in the genus Graphis.287 The term was first proposed by Michel Adanson in 1794.3
Cortex tissue made of closely compacted, agglutinated hyphae that forms a dense tissue layer.222
lobarioid lichen
An informal growth form category used for lichens previously separated in the family Lobariaceae and now classified as subfamily Lobarioideae within the Peltigeraceae.290
Plural lumina or lumens. An internal space or cavity in a structure, such as a cell, hypha, or septate spore.294
M
macrolichen
A lichen with a thallus large enough that its main characteristics can be identified without the use of viewing magnification; generally refers to foliose, squamulose, and fruticose species.295
Cuff-shaped; the term is used to describe soralia that break open to form a central perforation revealing a duct to the medullary cavity. Maniciform soralia occur in the genera Hypogymnia and Menegazzia.297
A purple insoluble lichen pigment, associated with the reference species Micarea melaena.301
Melaenida-red
A purple insoluble lichen pigment, associated with the reference species Micarea melaenida.42
melanotopelioid
A morphotype of corticolousthelotremoid lichens describing a type of apothecium structure resembling topeliopsidoid apothecia but characterized by a minimized thallus margin. The distinctive feature of melanotopelioid apothecia is the presence of "teeth" that are black and carbonized, at least on the external surface.302
Also microcrystal test. A method used to identify some lichen products that involves re-crystallization on a microscope slide from a range of solvents and the formation of crystals with characteristic shapes; the crystals are examined microscopically for identification. Although this technique has largely been supplanted by the more reliable and sensitive technique of thin-layer chromatography, there are certain situations where it is still useful.304
microlichen
A small lichen whose physical features cannot be distinguished without the aid of a 10X or greater viewing magnification;305 it generally refers to crustose and foliicolous species.306 The prefix "micro-" is also used to indicate small versions of particular growth forms, e.g. microfruticose or microfoliose.
The fungal part of a lichen,313 which combines with one or more phycobionts.314 The term was proposed by George Scott in 1957.5
mycophycobiosis
Also defined: mycophycobiont. A symbiosis where an ascomycete fungus is housed inside multicellular algae; the algae and fungus involved in this association are called mycophycobionts.315 Contrary to a lichen symbiosis, the fungal partner is the inhabitant, and the algal partner dominates.316
myriotremoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Myriotremoid lichens have immersed apothecia with small pores, and a smooth and more or less shiny thallus; this morphotype occurs in the glaucopallensgroup of genus Myriotrema.30
Also obovoid. Egg-shaped, with the narrower end at the base.317
obpyriform
Shaped like an inverted pear.318See related: pyriform.
ocellularioid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Ocellularioid lichens have prominent apothecia with wide pores; pores with a "finger" (columella); black walls (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in the genus Ocellularia.30
-oid
A suffix meaning "like" or "having the form of".319
Used to describe lichens that grow or proliferate in environments rich in bird excrement.272
ostiole
A small pore or opening; in lichens, it is used to refer to the paraphysis-lined cavity in a parathecium that ends in a pore, or more generally to any pore from which spores are released from an ascus-bearing fruit body.321
ostropalean
Referring to asci that are unitunicate with a thickened apex and a narrow canal ending in a pore; associated with species in the order Ostropales.322
Plural palisade plectenchymata. Also palisadoplectenchyma, plural palisadoplectenchymata. A type of plectenchyma in a cortex where the hyphae are arranged perpendicularly to the plane of the thallus.325
pallidostegoboloid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Pallidostegoboloid lichens have prominent apothecia with wide pores; pore filled with irregular structures; pale walls (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in wrightiigroup of the genus Stegobolus.30
A sterile, thread-like filament that that is attached at its base and grows vertically among the asci within a lichen's fruiting body (ascomata). These structures typically have slightly swollen tips and may be branched or unbranched, often containing pigments that contribute to the color of the fruiting body's disk.330
paraphysoid
A threadlike, sterile, hyphal structure similar to a paraphysis, but typically branched and often forming a network.331
paraplectenchyma
Plural paraplectenchymata. A type of plectenchyma comprising hyphae that are oriented in all directions; found in the cortex of many lichens.332
An organism that lives in close association with a host species, deriving benefits at the host's expense but not causing immediate harm; an intermediate state between symbiosis and parasitism.272
An informal growth form category used for lichens that are mostly foliose, often closely attached to the substrate, and have laminalapothecia and pycnidia; this group of features is characteristic of lichens previously classified in the genus Parmelia (in the broad sense).93
Also clypeate, scutiform. Referring to a rounded structure attached on the lower side at a single central point (often on a short stalk), with free edges.337
peltidiangium
A basket-like structure in which peltidia are produced.338
peltidium
A reproductive propagule found in the foliicolous lichen genus Gallaicolichen that is similar in form to a goniocystangium, but is unique in that the photobiont partner organizes the propagule and envelops (or nearly so) its mycobiont partner. The term is derived from the name of the involved green algal genus, Phycopeltis.338
pendant
Also pendent, pendulous. Hanging down, as in the fruticosethalli of genus Usnea, the beard lichens.339
Plural periphyses. A short, sterile hypha that develops from above the ascus and grows down a short distance, typically lining the internal walls of the ostiole in a perithecium.342
Also defined: exospore, epispore, mesospore, endospore. The colorless and usually gelatinous outermost layer of a spore.343 This transparent layer determines the spore's shape.344 The other four layers of a spore, going inward, are the exospore, epispore, mesospore, and endospore.343
Plural perithecia. A spherical or flask-shaped ascocarp that is sessile or partly immersed in the thallus, with a single opening (ostiole) and enclosed by a distinct wall; a characteristic of pyrenolichens.345 Although it was in 1831 that Elias Fries first applied the term perithecium to lichen fruit bodies, the word was originally coined by Christiaan Hendrik Persoon in 1794.346
Plural phenocortices, phenocortexes. A structure, similar to a cortex, containing hyphal fragments and dead, collapsed algal cells sloughed off from the algal layer.348
photobiont
Also defined: phycobiont, cyanobiont. The photosynthetic component of a lichen. This can be either a green alga (known as a phycobiont) or a cyanobacteria (known as a cyanobiont).349 The term "phycobiont" was proposed by George Scott in 1957.5
An organism whose morphology is determined by the nature of its photosynthesis; applied to lichen-forming fungi whose thalli have different forms with green algal versus cyanobacterial photobionts.350 The term was introduced by Jack Laundon in 1995 to address what he believed were deficiencies in related terms such as morph, morphotype, and photosymbiodeme.351
A historical lichenological term with multiple meanings. Originally introduced by Fries (1831) as "Phyco-Lichenes" for lichens morphologically resembling seaweeds. Later redefined by Massalongo (1855) for homoiomerous cyanobacterial lichens, then by Diels (1936) for lichens with Phycomycetes as their fungal partner. More recently proposed but discouraged as a term for green algal lichens, with "chlorolichen" recommended instead as a counterpart to "cyanolichen". Generally considered obsolete in modern lichenology due to its ambiguous history.98
phyllidium
Plural phyllidia. A small leaf-like or scale-like propagule that is corticate and has distinct upper and lower sides (i.e., it is dorsiventral); it originates from the margins or on the upper surface of thallus.353 Phyllidia occur in some species of the Lecanorales and the Peltigerales.354
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. Similar to chroodiscoid or leprocarpoid, but the difference lies in the presence of a free excipulum that forms a distinct double margin. It is exemplified in species such as Chapsa platycarpa and C. neei.359
platygonidium
Plural platygonidia.Photobionts that occur in star-shaped or circular colonies; now obsolete.360
plectenchyma
Plural plectenchymata. Fungal tissue made of twisted, intertwined hyphae; used as a general term to refer to all types of fungal tissue.361 The term (and the use of the prefixes "para-" and "proso-" to modify it) was proposed by Gustav Lindau in 1899.5See related: paraplectenchyma, prosenchyma, prosoplectenchyma, pseudoparenchyma.
plicate
Characterised by longitudinal folds forming pleats, often used to describe closely adjacent, markedly convex thallus lobes or elongated areoles that display a "folded" appearance.362
plurilocular
Also multilocular. Having many cavities or locules; used to describe spore structure.363
podetium
Plural podetia. An upright, hollow, stem-like structure bearing apothecia and sometime conidiomata; typically associated with the Cladoniaceae, particularly the genus Cladonia.363 The term was first used by Erik Acharius in 1803.3
POL test
A lichen test performed by shining a polarized light at a lichen structure in microscopic view; in the genus Hypogymnia, the presence (POL+) or absence (POL−) of POL-sensitive crystals in the hypothecium is a useful character to help distinguish species.364
polarilocular
Also placodiomorphic,256polar-diblastic, polaridiblastic, polaribilocular, polocellate. A spore divided into two components (locules) separated by a central septum with a perforation or isthmus.365366 The term was first used by Wilhelm Körber in 1855 (as "polari-dyblastae") to describe the spores of Rhizocarpon and Umbilicaria. It was anglicized to "polari-bilocular" by William Mudd in 1861, and finally shortened to polarilocular by the Henri Olivier in 1882.4
Polychroa-brown
An orange-brown to ochre insoluble lichen pigment, associated with the reference species Bacidia polychroa.56
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. This morphotype is similar to ocellularioid, but with a very narrow pore that resembles the opening of a true perithecium. Despite this, the hymenium remains organized in a distinct, compact layer with paraphyses and asci of similar height. Examples include Leucodecton bisporum, L. compunctellum, and T. patwardhanii.368
praestantoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Praestantoid lichens have large and prominent apothecia with small pores; pores with "finger" (columella); black walls (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in the praestansgroup of the genus Ocellularia.30
Sticking out from the surface of the thallus.370 A more precise definition has been suggested by Aptroot and Lücking, who propose that the term applies to ascomata and pseudostromata that are more than 1/2 above the level of the thallus, and have a base that is expanded outwards.183
proper margin
Also proper exciple, true exciple, ectal excipulum, medullary excipulum, proprium. A ring of tissue around the disk of a lecanorineapothecium; this tissue, which originates from the medulla, is not lichenized, and is internal to the thalline margin (if present).371 The term "proper margin" was first used by Erik Acharius in 1803; in 1825 Elias Fries changed the noun and called it "proper exciple".3
Plural prosenchymata. A type of plectenchyma in which the constituent fungal hyphae are arranged parallel to each other, such that individual hyphae can be clearly distinguished using microscopy.372
prosoplectenchyma
Plural prosoplectenchymata. A type of plectenchyma, common in the thalluscortex of lichens, in which the constituent fungal hyphae are aligned in a particular direction.372
A fungal layer upon which an algae-containing thallus may develop, lacking photobiont; usually white, brown, or black, and found between the areoles and at the growing margins of crustose lichens.373 The term was first used by Georg Meyer in 1825.3
prototunicate
A form of unitunicateascus in which the wall breaks down before maturity (thus releasing its ascospores), and which lacks differentiated apical structures.374
proximal
Positioned close to a point of origin or near the center of a body.375
pruina
A powdery, frost-like or flour-like deposit on a surface. In lichens, pruina is often the result of the accumulation of crystalline hydrates of calcium oxalate, of lichen products, or sometimes of the dead or dying cells of the epinecral layer.376
Also pseud-. A prefix meaning "false";377 used in terminology to denote something is false, or that one structure resembles something else, such as the pseudocyphella resembling the cyphella.375
Plural pseudocortices, pseudocortexes. A boundary layer of the thallus containing distinct hyphae that are not organized into a regular tissue structure;378 sometimes used to refer to the false cortex present on the outer layer of pseudopodetia, such as those found in the lichen Pycnothelia papillaria.379
Plural pseudocyphellae. Small openings in the cortex of a lichen, where the medulla is exposed to air, and there are no specialized cells surrounding the cavity.380 The term was first used by William Nylander in 1858.4
pseudoisidium
Plural pseudoisidia. An outgrowth on the surface of a lichen thallus that somewhat resembles an isidium, but lacks photosynthetic cells; pseudoisidia are common in the genus Pseudocyphellaria.381
pseudoparaphysis
Also cataphysis. A paraphysis-like hypha that forms in the locule or perithecial cavity before the formation of the ascus; it grows downward from the top of the cavity to the base of the ascomata.382
pseudoparenchyma
Plural pseudoparenchymata. A type of plectenchyma made of tightly packed, angular or polyhedral cells.382
A lichen with flask-shaped fruiting bodies (perithecia) that develop from the fungal partner. Originally thought to form a natural group, molecular studies have shown pyrenocarpous lichens to be highly polyphyletic, evolving independently in multiple fungal lineages. Most belong to Chaetothyriomycetidae (e.g., Verrucariales, Pyrenulales), with some in Dothideomycetes (e.g., Arthopyreniaceae, Trypetheliaceae) and others unusually placed in Lecanoromycetes (e.g., Porinaceae, Protothelenellaceae, Thelenellaceae). Pyrenocarpous lichens are notably absent from the classical pyrenomycete class Sordariomycetes. This diverse group demonstrates that ascoma morphology alone is insufficient for determining evolutionary relationships, with convergent evolution of perithecial fruiting bodies occurring multiple times across fungal lineages.393
Also recurvate, reflexed.398 Curved or bent back; in lichens, these terms are used to describe the tips of branches or lobes that are curved up or down, or back onto themselves.399
redingerioid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Redingerioid lichens have immersed apothecia with linear slit; slit filled with irregular structures; black walls (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in the genera Redingeria and Stegobolus.30
reimnitzioid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Reimnitzioid lichens have open apothecia with erect lobules, and a rough thallus containing crystals; this morphotype occurs in the genus Reimnitzia.30
A single hyphal strand on the thallus underside that serves as an attachment organ.403
rhodostromoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Rhodostromoid lichens have large and prominent apothecia with small pores; pore with "finger" (columella); black walls and pigment (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in the rhodostromagroup of the genus Ocellularia.30
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. This morphotype resembles the leprocarpoid but features recurring hymenia that produce layered excipula, which eventually cover the disk; examples include Chapsa aggregata and C. albomaculata.413
scabrous
Also scabrose, scabrid, scabridous. With a crusty, rough surface often resulting from the accumulation of dead cortical material.414390
schizidium
Plural schizidia. A scale-like propagule originating from the upper layers of a lichen thallus.415 The term was proposed by Josef Poelt in 1965.5
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Schizotremoid lichens lack apothecia and have schizidia, and a smooth, more or less shiny thallus; this morphotype occurs in the genus Stegobolus.30
Schweinitzii-red
A dark red insoluble lichen pigment, associated with the reference species Bacidia schweinitzii.42
scleroplectenchyma
Plural scleroplectenchymata. A type of plectenchyma comprising thick-walled hyphae that are stuck closely together; present as a component of the stereoma tissue supporting the thallus in the genera Cladonia and Alectoria.415
scrobiculate
Having large, shallow depressions that are narrowly separated by rounded ridges.195Compare: faveolate, foveolate.
Plural scyphi. The cup-shaped part at the tip of a lichenized podetium, common in the genus Cladonia.417 The term was first used by Johann Dillenius in 1742, and later adopted by Carl Linnaeus in 1753.4
Lacking a stem.421 A more precise definition has been suggested by Aptroot and Lücking, who propose that the term applies to ascomata and pseudostromata that are more than 3/4 above the level of the thallus, with a constricted base.183
seta
A stiff hair or bristle-like structure, typically thick-walled and sharp-pointed, found on some lichens.422
sibling species
Closely related species that are morphologically indistinguishable but can be distinguished by non-morphological traits, such as chemistry or genetic differences. Initially defined as species recognized mainly through cryptic or non-morphological discontinuities, the concept has evolved to specifically refer to cryptic species that form a monophyletic group, meaning they share a common ancestor not shared with any other species. This concept is a subset of the broader terms species pair and "cryptic species".423
Plural soralia. A part of the thallus where the cortex has cracked or broken down and soredia are produced. Soralia can be further characterized as diffuse if they are spread out on the upper thallus surface as a continuous layer, or delimited if they are confined to a more restricted area. If soralia originate in tubercules they are tuberculate, while they are fissural if they are created in fissures.429 The term was proposed by Johannes Reinke in 1895.5
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Sorediotremoid lichens lack apothecia and have soralia, and a smooth, more or less shiny thallus; this morphotype occurs in the genera Myriotrema and Ocellularia.30
soredium
Plural soredia. A powdery to granular reproductive propagule that is not covered with a well-defined cortex (in contrast to isidia, and contains both algal (photobiont) and fungal (mycobiont) components.429 The term was first used by Erik Acharius in 1803.3
Two lichen species that are identical morphologically, anatomically, and chemically, but can be distinguished by their sexual versus asexual reproductive strategies; the fertile taxon is known as the primary species, while the vegetatively reproducing taxon is known as the secondary species.369 The use of molecular methods to analyze putative species pairs has shown that the underlying phylogenetic situation is more complex than had been assumed, and not necessarily correlated with reproductive strategy.431See related: sibling species.
spermogonium
Also spermagone, spermagonium. In lichenology, an obsolete term for pycnidium.432
A small spine; in some fruticose lichens of the Lecanoromycetes, it refers to a small cylindrical outgrowth, with a narrow base, in which the central axis is not connected with the central axis of the main branch.433
spinulose
Also spinulous. Covered with or having small spines (spinules) or spiny projections.433
A lichen species that is extremely similar (or identical) in external morphology, anatomy, chemistry, and spore size to another, but that is placed in a different genus solely based on differences in spore septation and/or spore colour. The term was introduced by Michael Wirth and Mason Hale in their 1978 monograph about the Graphidaceae, a family in which sporomorphs are common.437
In this spot test, a red color resulting from the application of C on Dirina massiliensis f. sorediata indicates the presence of erythrin.438source ↗
spot test
A spot analysis used to help identify lichens; it is performed by placing a drop of a reagent on different parts of the lichen and noting any color change associated with application of the reagent. The four most common tests are C, K, KC, and PD.439
squamule
A small, flattened, scale-like structure that forms part of the thallus of certain lichens.440
squamulose lichen
A lichen with a thallus made of numerous small scales or lobes; intermediate in form between crustose and foliose lichens.440
squarrose
Brush-like, with many short, more or less perpendicular lateral branches. In lichenology, used to refer to rhizine structure.441
stegoboloid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Stegoboloid lichens have prominent apothecia with wide pores; pore filled with irregular structures; black walls (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in the genus Stegobolus.30
Plural stromata. A dense mass of vegetativehyphae that supports spore-bearing structures.443 In lichens, the stroma is often hard and carbonaceous.403
sub-
A prefix meaning "below", "under", "somewhat, or "almost".444 Also used in front of names of taxonomic ranks to indicate intermediate categories, e.g. subspecies or subgenus.445
Also subicule.Plural subicula. A layer of loosely-compacted mycelia that covers the substrate and cushions fruiting bodies such as apothecia and perithecia.446 The texture of the subiculum can be described as net-like, wool-like, or crust-like.444
substrate
Also substratum; plural substrata. The surface or base upon which a lichen grows or is attached. Although the terms substratum and substrate are often used equivalently in lichenology, the latter term has different meanings in microbiology and in enzymology.447
subulate
Slender and narrowing to a fine point; awl-shaped.448
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus morphology. Tenuitremoid lichens have immersed apothecia with small pores and a black margin; pore with "finger" (columella); black walls (viewed in microscopic section); and a smooth, more or less shiny thallus. This morphotype occurs in the genus Clandestinotrema.30
tegulicolous lichen
A lichen that lives on tiles.450 In general, these are calcicolous lichens or lichens that are indifferent as to their substrate.451
Describing a cylindrical or rod-like structure that is round in cross-section.428
teretiform
Describing a shape that is nearly cylindrical or rod-like, similar to but not exactly terete; circular in cross-section, gradually tapering towards one end.453
Also thalline exciple, excipulum thallinum. A rim of tissue around the disk of a lecanorineapothecium; this tissue, external to the inner proper margin, is made of tissue with a structure similar to that of the thallus.455 The term "thalline margin" was first used by Erik Acharius in 1803; in 1825 Elias Fries changed the noun and called it "thalline exciple".3
Plural thalloconidia. A dark brown, smooth to wrinkled propagule arising directly from a thallus, particularly the lower cortex and/or the rhizines. They are found in some species of Umbilicaria, and similar structures arise from the prothallus of some species in the genera Protoparmelia, Rhizoplaca, and Sporastatia. Thalloconidia have distinct cell layers in their walls, and comprise between 1 and about 2500 cells.457458
Plural thalli. The body of a lichen,460 made up of both fungal and algal or cyanobacterial cells.461 The term was first used by Erik Acharius in 1803.3
thallyle
A small thallus that originates from rhizomorphs; typically associated with the genus Umbilicaria.428
A morphological group of lichens within the Graphidaceae, the largest family of crustose lichens.463 Thelotremoid lichens are characterized by immersed-erumpent, rounded ascomata, non-branched to slightly branched paraphyses, mostly distoseptate ascospores, and mostly a prosoplectenchymatousexcipulum. Thelotremataceae, a traditional family of lichens, has been included in Graphidaceae, and its species are now informally accepted as thelotremoid lichens.463
tholus
Plural tholi.Also dome. The apical, often thickened part of the inner wall in a bitunicate ascus.464
tomentum
Plural tomenta. Also defined: tomentose. A layer of short interwoven or coiled fungal hyphae with a texture similar to velvet. In lichens, the tomentum projects from the lower cortex and serves to help it attach to its substrate. Structures with this type of hyphae are called tomentose.465 Tomentose surfaces are found in foliose genera such as Lobaria, Pseudocyphellaria, and Sticta.466
topeliopsidoid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. It pertains to lichens where the apothecia are either prominent or sessile, often hidden between the substratum, and they open with multiple, typically regular "teeth" that stay relatively curved over the hardly visible disk. The margins tend to peel off, meaning the overlaying thallus cortex separates from the underlying marginal thallus tissue, but no distinct, clean split between thallus margin and excipulum is formed. This morphotype is seen in species like Chapsa meridensis and Topeliopsis.467
trabecula
Plural trabeculae. In the genus Umbilicaria, they are rib- or strap-shaped structures radiating outward from the umbilicus that merge towards the mid-zone of the thallus undersurface.276
trentepohlioid
Also trentepohlialean.468 Resembling or belonging to the green algal genus Trentepohlia; trentepohlioid cells are filamentous (elongated and cylindrical), multicellular, and have a yellow to orange colour.469
Also defined: funiculus, umbilicus, umbilical cord. A lichen with a concave, circular, leafy thallus that is joined to its substrate only by its central part, called an umbilicus, umbilical cord or funiculus.472473
A type of ascus with a single functional layer; the rigid internal and external wall layers do not separate during release of the ascospores. Most ascomycetes have unitunicate asci.477
urceolarioid
A morphotype of corticolousthelotremoid lichens used to describe characteristics of apothecial and thallus structure. In this, the fruiting bodies are noticeable to sessile and have a narrow pore with a smooth margin, through which the disk and excipulum are not visible. This morphotype can be observed in Thelotrema isidiophorum, T. subweberi, and T. weberi.478
Deeply cup-shaped or urn-shaped; in lichens, the term is used to describe some apothecia with a sunken hymenium and elevated parathecium that forms a narrow mouth.479
A lichen test performed by shining a long-wavelength ultraviolet light (350 nm) at a lichen structure to check if it fluoresces; a positive test (abbreviated as UV+) indicates the presence of certain lichen products. Xanthone compounds in the cortex tend to fluoresce yellow, orange, or red, while depsides and depsidones in the medulla fluoresce blue to white.481
A lichen not attached to a substrate, typically able to be blown around by wind.482
vegetative
Also assimilative. Having to do with the growth phase of an organism before reproduction, including spore germination, growth, development and asexual multiplication.483
A lichen in which the photobiont partner is yellow-green algae (class Xanthophyceae); an example is the lichen formed by the fungus Verrucaria funckii and the yellow-green alga Heterococcus caespitosus.347
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