Most Caliciaceae grow on
bark,
dead wood, or
rocks. Some members of this family, particularly those of the
type genus, Calicium, are characterized by the presence of thin-walled and short-lasting
asci (spore-bearing cells) and a mazaedium, which is an accumulation of loose, maturing
spores covering the surface of the
fruiting body. The resulting passive spore dispersal is relatively rare amongst the Ascomycota. The mazaedium, usually black, either sits atop a long thin stalk, or rests on (or is sometimes immersed within) the surface of the lichen
substrate. Many other Caliciaceae species generate spores in an
apothecium, which typically resembles a flattened black disc.
Caliciaceae was
circumscribed in 1826 by the French botanist
François Fulgis Chevallier. He wrote about the family: "The Calicinees are a small group of plants, the growth of which has misled botanists. They are small parasitic fungi on the crusts of lichens, mainly on Variola and common porin, and on dead canes."[2] The
type genus of the Caliciaceae is Calicium, originally
circumscribed in 1794 by
Christiaan Hendrik Persoon; this genus is itself
typified by Calicium viride.[3] Buelliaceae and Pyxinaceae are historical families created to contain
taxa that are now included in the Caliciaceae.[1]
Two other calicioid families with "Caliciaceae" in their name –
Microcaliciaceae (order
Pertusariales, class
Lecanoromycetes) and
Mycocaliciaceae (order
Mycocaliciales, class
Eurotiomycetes) – contain species formerly considered to be closely related to the Caliciaceae. The
monogeneric Microcaliciaceae has non-lichenized, calicioid species that are parasites on lichens or free-living colonies of algae, while Mycocaliciaceae contains non-lichenized calicioid fungi lacking a mazaedium and utilising active spore dispersal.[4]
Classification
The Caliciaceae and other morphologically similar
pin lichens with mazaedium-forming ascomata featuring passive spore dispersal used to be grouped together in the order Caliciales, which was for a long time considered to be a model example of a
monophyletic grouping of taxa.[5] Historically, the family has also been placed by various authors in the orders
Coryneliales,
Helotiales, and the now-obsolete Sphaeriales, depending on which
phenotypic characteristics were considered to be the most important.[6]
The Swedish lichenologist
Leif Tibell spent much of his career studying calicioid lichens, and used a variety of techniques to help him understand relationships of taxa in this group,[7] including
phenetic and
cladistic analyses of
morphology, and investigation of
secondary chemistry. He suggested in 1984 that the order was
polyphyletic (i.e., it did not originate from a single
common ancestor) and that the main identifying features of the Caliciales had
evolved independently in several different unrelated groups.[8] He restricted the order to three families (Caliciaceae,
Mycocaliciaceae, and
Sphinctrinaceae) that he considered to be the "core" of the group.[8][9] Preliminary
phylogenetic analysis showed that Mycocaliciaceae and Sphinctrinaceae belonged to the class
Eurotiomycetes, while Caliciaceae appeared to group with the order
Lecanorales.[5] The proposition that mazaediate fungi are dispersed throughout the Ascomycota was confirmed later in several molecular phylogenetic studies.[5][10][4] The six genera that were included by Tibell in the Caliciaceae in his 1984 proposed classification of calicioid fungi (Acroscyphus, Calicium, Cyphelium, Texosporium, Thelomma, and Tholurna)[8] are still in the family today.[11]
Phylogenetics
The Caliciaceae and the
Physciaceae were shown to be closely related in molecular studies.[12][13] Both of these families were tentatively placed in the
Teloschistales as part of the suborder Physciineae.[14] Since the mazaedia-producing species of the Caliciaceae were nested within the genera Dirinaria, Pyxine, and Physcia (all once contained in the family Physciaceae), some authors treated all the members of the Caliciaceae and Physciaceae as one family, and the name Physciaceae was proposed for
conservation in 2002.[15] With the appearance of additional phylogenetic studies since then, however, a two-family concept of Caliciaceae and Physciaceae has been preferred by most authorities. In 2012, the suborder Physciineae was promoted to ordinal status and the name Caliciales was resurrected.[16] In its modern circumscription, the order Caliciales contains these two families.[17] A large molecular study of the Caliciaceae-Physciaceae
clade published in 2016 has helped to sort out natural relationships in this group, and more clearly define generic delimitations.[18]
The genus Culbersonia, previously classified in the Physiaceae because of its morphological resemblance to Physconia, was shown to be a member of the Caliciaceae in 2019. In phylogenetic analysis, it groups together in a
clade with Pyxine and Dirinaria. These three genera are distinguished from other Caliciaceae in the appressed
foliose growth form (like small leaves pressed flat against the substrate), the absence of a mazaedium, and ecologically by their predominance in the
subtropics and
tropics.[11]
Description
The lecidiene ascomata of the boreal button lichen (Buellia disciformis, left) are carbonized, discoid, and sessile. The mazaediate ascomata of the shrub stubble lichen (Allocalicium adaequatum, right) rest atop short, black stalks.
The
thallus, when present, is
crustose, with a texture that is verrucose (warty), granular (grainy), or
areolate. Its colour is typically grey, yellow, or greenish. Sometimes it is immersed within the outer layers of the bark of its host. The
ascomata are more or less spherical or hemispherical, situated atop a long stalk in some species, but
sessile in other species. When it is present, the stalk is usually melanized (blackened).[19] The form of the ascomata is either apotheciate (consisting of an
apothecium) or mazaediate.[1] The apothecium consists of the
asci (spore-bearing cells) and associated
hymenium, and the sterile, structural, and supportive part of the apothecium, called the excipulum. In apotheciate Caliciaceae species, the apothecium is typically lecidiene (lacking a margin around the thallus, or having a margin made of the excipulum itself), rather than lecanorine (rounded with a protruding margin). The tissue structure of the excipulum is either prosoplectenchymatous (comprising long, narrow, wavy, parallel hyphae) or paraplectenchymatous (a cell arrangement where the hyphae are oriented in all directions), and is
hyaline (translucent) to dark brown.[1] The genus Acroscyphus, which contains the single widespread but rare species A. sphaerophoroides, is a peculiar exception to the typical morphology of the Caliciaceae: it has a finger-like (dactyliform) thallus, immersed ascocarps on
podetia (hollow stalks), and a yellow to orange
medulla.[20]
The asci of Caliciaceae species are cylindrical to broadly club-shaped. They are attached to
croziers, which are hook-shaped structures on cells that form at the base of the asci. The asci have thin walls and lack any internal structures at the tip. As a result, they last for only a short time before they degrade, and the ascospores within are released passively in a mazaedial mass.[19] The hamathecium (a term that refers to the tissues interspersed between the asci in the
hymenium) consists of unbranched to slightly branched
paraphyses that are
amyloid.[1] There are usually eight spores per ascus, although sometimes this is reduced to four, or increased to 16–32 per ascus.[1] The ascospores are dark brown, with a surface that is either smooth or ornamented with remnants from the rupture of the outer wall layers. They have either zero or one
septa.[19] The spores of Texosporium lichens have a unique ornamentation that is created by paraphyses that stick to the surface; this feature may help provide protection against desiccation or
DNA-damaging radiation encountered when exposed in sunny habitats.[21] The
conidiomata produced by Caliciaceae species are in the form of
pycnidia. The
conidia lack a septum, are rod-shaped (bacillar) to thread-shaped (filiform) in form (often curved), and are hyaline.[1]
As of December 2023[update],
Species Fungorum accepts 39 genera and 666 species in the family Caliciaceae.[23] This is a list of the genera in the Caliciaceae, based on a 2020 review and summary of fungal
classification by Wijayawardene and colleagues.[17] Following the genus name is the
taxonomic authority (those who first circumscribed the genus; standardized
author abbreviations are used), year of publication, and the number of species:
Some genera that have been until relatively recently classified as members of the Caliciaceae have had their status reassessed in light of molecular phylogenetic studies. For example, CypheliumAch. was
synonymized with Calicium in 2016 when it was discovered that its type species grouped with the latter genus.[18]Hafellia was placed in synonymy with Buellia when a proposal to replace the conserved type of Buellia, B. disciformis, with B. aethalea,[60] was declined by the
Nomenclature Committee for Fungi.[61] That proposal had attempted to retain B. disciformis as the type for Hafellia, so that the name could continue to be used for a distinctive group of crustose lichens with thickened ascospore walls that had historically been treated in Buellia.[60]
Habitat and distribution
Collectively, Caliciaceae species have a
cosmopolitan distribution, although they are especially predominant in
temperate and
tropicalmontane areas. Most species form lichens that
grow on bark or dead wood,[19] although some
grow on rocks.[1] In contrast, Texosporium is part of the
biological soil crust communities found in
grasslands, and grows on
cow dung, soil, and
detritus.[18] One rare species known only from a single locale in Sweden, Calicium episcalare, is
parasitic on the common lichen Hypocenomyce scalaris.[62] Like most calicioid species, the Caliciaceae tend to avoid competition with other lichens and often grow in
microhabitats neglected by other lichens. Examples include: the side of a tree not inhabited by other
corticolous species, in the cracks of deep fissures in bark, or woodpecker holes. Because of this preference for neglected locales, and their generally small size, the calicioid lichens tend to be overlooked by collectors and the group in general is poorly known.[63]
Caliciaceae is one of the families whose species are most often found in
mangrove forests of
Calabarzon (Philippines).[64] Similar results were reported in studies on mangrove forests in India,[65] and the
Gulf of Thailand,[66] where the genera Dirinaria and Pyxine were found to be amongst the most common foliose lichens. The lichens found in the mangrove ecosystem tend to be salt-tolerant and moisture sensitive.[64] Using
next-generation sequencing techniques to detect the genetic signature of organisms, Caliciaceae species were identified as some of the most common
endolithic lichens (crustose lichens that grow inside solid rock) found in the
McMurdo Dry Valleys in Antarctica. This region features one of the most harsh environments on earth, with wide variations in temperature, extreme
aridity, limited nutrients, and high levels of
solar and
UV radiation.[67] The
photobiont partner of the Caliciaceae is usually from the green algal genus Trebouxia,[19] although Stichococcus has been recorded with Calicium.[68]
Although there are no Caliciaceae species that are known to have economic significance,[19] some of them have been exploited for scientific purposes. In a 1992 Swedish study, Allocalicium adaequatum (then a member of Calicium) was proposed as one of several
bioindicator species that could be used to help assess forest continuity in
boreal coniferous forests.[76] A similar study conducted in the
Acadian forest ecoregion of
Atlantic Canada found several Caliciaceae species appropriate for determining continuity in
old-growth forests.[77]
Buellia frigida, a crustose species that grows on rocks in the harsh
Antarctic climate, has often been used as a
model organism in
astrobiology research. This
extremophile lichen has been exposed to conditions simulating those encountered in space and on celestial bodies like
Mars, including
vacuum,
UV radiation, and
extreme dryness. B. frigida has demonstrated resilience to these space-related stressors, making it a candidate for studying how life can adapt to and potentially survive in extraterrestrial environments.[82]
Fossil record
A fossil belonging to Calicium was described from
Baltic amber dating to 55–35 million years ago (Mya).[83] This and other fossils were used to estimate the date of the split between the Caliciales (i.e., the Caliciaceae-Physciaceae clade as proposed by Gaya and colleagues in 2012[16]) and the
Teloschistales. In their analysis, this occurred in the
Middle Jurassic, around 171 Mya.[18] Other fossils have since been found. In 2018, three fossils assigned to Calicium were reported from European
Paleogene amber.[84] A Baltic amber fungus fossil, originally collected by
Robert Caspary and assigned to the genus Stilbum (family
Chionosphaeraceae) in 1886, was reassessed as a member of the Caliciales in 2019, as Calicium succini. Because it is considered to be "well-preserved and reliably identifiable", it is valuable for use in evolutionary studies that estimate the
divergence times of fungal
lineages.[85]
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Cited literature
Marbach, Bernhard (2000). Corticole und lignicole Arten der Flechtengattung Buellia sensu lato in den Subtropen und Tropen [A study of corticolous and lignicolous species of the lichen genus Buellia s.l. in subtropical and tropical regions]. Bibliotheca Lichenologica (in German). Vol. 74. J. Cramer. pp. 1–384.
ISBN978-3-443-58053-7.