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The Cladoniaceae are a family of lichen-forming fungi in the order Lecanorales, comprising about 560 species distributed amongst 18 genus. This family is one of the largest among lichen-forming fungi and is globally distributed, from Arctic tundra to tropical rainforests, favouring humid environments while being intolerant of arid conditions. Molecular phylogenetics has significantly advanced the understanding of their complex taxonomic history, revealing intricate evolutionary relationships and leading to a refined classification. Notable members include reindeer moss and cup lichens of the genus Cladonia, which consist of about 500 species and forms a significant part of the diet for large mammals in taiga and tundra ecosystems.
A distinctive feature of many Cladoniaceae species is their dimorphic thallus: a scaly or crust-like form and a (shrub-like) secondary form known as a podetium or . These lichens typically grow on soil, decaying wood, or tree trunks, with a few species found on rocks. They form symbiosis associations with green algae, usually from the genus Asterochloris. The family is known for its diverse secondary metabolites—over 70 have been identified—which play roles in species identification and ecological functions such as protection against UV radiation and herbivore deterrence. Genomics studies have uncovered significant variation in mitochondrial DNA among Cladoniaceae species, contributing to the understanding of their evolution and diversity.
Some Cladoniaceae species have economic value, particularly in decorative uses such as floral arrangements and model-making due to their unique structures. Six species are included in the International Union for Conservation of Nature's Red List of Threatened Species, facing threats from habitat loss, climate change, and human activities. Conservation efforts are ongoing to protect these vulnerable species.
Cladoniaceae is now one of the largest families of lichen-forming fungi, with about 560 species distributed amongst 18 genera. The type genus is Cladonia, circumscribed by the Irish physician and botanist Patrick Browne in 1756. He included eight species in his new genus. Of their occurrence, he wrote: "All these species are found in great abundance in the mountains of Liguanea: they grow mostly on the ground, among other sorts of moss, but a few ... species chiefly are found upon the decaying trunks of trees."
It is well known that reindeer feed on lichens, which has led to the widespread but misleading name "reindeer moss". This common name, along with "reindeer lichen" and "caribou lichen", is typically applied to the ground-dwelling, mat-forming species that were previously classified in the genus Cladina. Cladonia species with cup-shaped structures borne at the tips of vertical stalks (podetia) are often known as "pixie cups". Examples include the "boreal pixie cup" ( C. borealis), the "finger pixie cup" ( C. digitata), and the "red-fruited pixie cup" ( C. pleurota) Additional names alluding to these characteristic structures include the "powdered funnel lichen" ( Cladonia cenotea), and the "trumpet lichen" ( C. fimbriata). Some names reference the reddish hue of their fruiting structures, such as "British soldiers" ( C. cristatella), the "jester lichen" ( C. leporina), and the "lipstick powderhorn" ( C. macilenta).
Within these clades, several have been identified, such as the Cladonia gracilis group and the Cladonia humilis group. These complexes often include morphologically similar species that are difficult to distinguish based on traditional taxonomic characters. Molecular studies have revealed that many of these complexes contain cryptic species diversity, with genetically distinct lineages that are not easily recognisable morphologically.
Focused molecular studies have further refined the understanding of specific groups within Cladoniaceae. For instance, detailed analyses of the Cladonia furcata complex have revealed high levels of homoplasy (the occurrence of similar traits due to convergent evolution rather than shared ancestry) in the morphological characters traditionally used for species delimitation. Similarly, studies on the Cladonia cariosa group and the Cladonia pyxidata group have uncovered previously unrecognised diversity and highlighted the need for integrative approaches combining molecular, morphological, and chemical data in species delimitation. These phylogenetic studies have also shed light on biogeographic patterns within Cladoniaceae. For example, some clades show distinct geographic distributions, such as a group of predominantly African species within clade Perviae, while others have more cosmopolitan distributions. Morphologically distinct genera like Carassea, Pycnothelia, and Metus form a sister clade to Cladonia. These genera share some morphological and chemical traits, such as dimorphic thalli and the production of atranorin. However, their geographic distributions vary, with Carassea being endemism to Brazil, while Pycnothelia has a bipolar distribution (i.e., found in the high latitudes of both hemispheres) and Metus is found primarily in Australasia.
In 2018, Ekaphan Kraichak and colleagues used a technique called temporal banding to reorganise the Lecanoromycetes, proposing a revised system of classification based on correlating taxonomic rank with geological (evolutionary) age. They synonymised the families Squamarinaceae and Stereocaulaceae with the Cladoniaceae, resulting in a large increase in the number of genera and species. The Squamarinaceae had already been included in the Cladoniaceae by previous authors. Although this reorganisation has been used in some later publications, the folding of the Stereocaulaceae into the Cladoniaceae was not accepted in a recent analysis. Robert Lücking highlighted that merging the two families under the name Cladoniaceae is not permissible without a formal conserved name proposal because Stereocaulaceae, established in 1826, predates Cladoniaceae, which was established in 1827. According to the rules of botanical nomenclature, the earliest validly published name has priority and must be used when two families are combined unless an exception is granted. This means that if the families were merged without a conservation proposal, the combined family would have to be named Stereocaulaceae due to its earlier establishment. In a 2021 treatment of the British and Irish Cladoniaceae, the authors also keep these families separate, noting "both families are monophyletic and easily distinguishable on both morphological and molecular terms".
The ascomata are in the form of an apothecium, and are , meaning they are of the type – light in colour and soft in consistency. They often have a reduced margin. Their colour is typically dark brown (sometimes pale brown), red, ochraceous, or black. The (referring to all between the asci in the hymenium) consists of sparsely branched paraphyses, and is amyloid, indicating that staining blue to blue-black with iodine-based reagents. The ascus (spore-bearing cells) are somewhat , meaning they have two layers that separate during ascus dehiscence. The ascus structure consists of an and a tube (both of which are amyloid), which is cylindrical to (club-shaped). number eight per ascus, and they are usually non-septum (lacking internal partitions), ellipsoid to more or less spherical in shape, hyaline (translucent), and non-amyloid. Except for a few genera that produce septate ascospores ( Calathaspis, Pycnothelia and Pilophorus), the hymenium does not generally have that are useful in taxonomy. The conidiomata (asexual fruiting bodies) are in the form of pycnidia; the conidia (asexual spores) are non-septate, usually (thread-like), and hyaline.
Cladoniaceae species begin development with the formation of a prothallus – a fungal layer upon which an alga-containing thallus will develop. It comprises the from the germination of an ascospore. After the protothallus contacts the alga, lichenisation begins with the development of small squamules (scale-like thallus segments) that make up the primary thallus, which is squamulose (scaly) or crustose (crustose-like). The secondary thallus consists of vertical structures that are shrubby and hollow, although they can be solid in rare cases. If these structures are made of generative tissue, they are called podetia; when they are made of vegetative tissue, they are called pseudopodetia. The morphology of these structures determines to a large part the taxonomy of the Cladoniaceae, which can range from simple to complex branching patterns. Cladonia minisaxicola, found in the mountains of Bahia (Brazil) is the only species in that large genus that is completely crustose and does not develop podetia.
The tips of the podetia have a wide range of morphology in the Cladoniaceae. They can be straight, tapering from a wide base to a point (called ), or flaring on cup-shaped . The scyphi are sometimes closed, or have a central perforation, forming structures called funnels. The podetia are slow-growing, with an annual growth rate generally ranging from 1 to 15 mm.
Branching in the Cladoniaceae occurs on the podetium, driven by the growth patterns of fungal meristem tissue at its tip. There are two main branching patterns: in one, branches emerge later from a large meristem that changes shape, while in the other, smaller meristems split early but keep their shape. These growth patterns help scientists understand the evolutionary relationships within Cladoniaceae. A shift from isotropy growth (uniform in all directions) to anisotropy growth (different in various directions) allows for more flexibility in development. This transition, from symmetrical to more irregular growth, may signal evolutionary adaptations. Despite these changes, the branching processes remain highly consistent even among species in the family that are not closely related.
Myelorrhiza was transferred from the Cladoniaceae to the Ramalinaceae by Sonja Kistenich and colleagues in 2018. Neophyllis, originally classified in the Cladoniaceae, was transferred to Sphaerophoraceae in 1999.
In his 2000 monograph on the Cladoniaceae of the Neotropical realm, Ahti included 184 species in 4 genera, and showed that South America is a hotspot of biodiversity for genus Clanodia. Bioclimatic variables significantly influence the distribution of Cladoniaceae species richness in the Neotropics, particularly under conditions of low precipitation and temperature, and high climatic variability. Areas with stable climates and higher temperatures and precipitation tend to support greater species richness. Twenty-six Cladoniaceae species (25 Cladonia and 1 Cladia) are known to occur in the Galápagos Islands. There, some species form mats on lava flows that have developed little soil. A 2013 monograph of Northern European Cladoniaceae treated 100 species (95 Cladonia, 4 Pilophorus, and the monotypic genus Pycnothelia). In the 2021 key to lichen species in Italy, 86 Cladoniaceae are included. In Bulgaria, 55 species in two genera were reported in 2022. In a study of the lichen biodiversity in Kazakhstan's Burabay National Park, the Cladoniaceae made up about 30 percent of the species diversity.
In western North America, the Coast Mountains of British Columbia act as a key phytogeography barrier. This results in distinct oceanic and continental taxa groupings on either side. The research also suggests that the southern boundaries of certain species may be determined more by historical rather than purely ecological factors, indicating possible range expansions. The highest diversity of Cladonia species is found in British Columbia between 52°N and 56°N, an area that was covered by glaciers until about 10,000 to 13,000 years ago. The Cladoniaceae biodiversity in this region represents the richest assemblage of the family in western North America. Species diversity declines sharply south of 52°N, with a loss of three to five taxa for each degree of latitude.
The glacier history of the region has played a crucial role in shaping the current distribution of Cladoniaceae. During the Pleistocene, most species likely survived in areas south of the Cordilleran ice sheet, with some persisting in , arctic regions, or small coastal refugia. This glacial legacy is still evident in the family's current distribution patterns. Cladoniaceae show a preference for specific habitats, with greater floristic and chemical diversity observed in humid areas and lower forested elevations compared to arid regions and alpine zones. This suggests that many species in the family are adapted to environments with relatively short periods of desiccation. The post-glacial period has seen significant changes in the distribution of Cladoniaceae. Many species that likely existed in Washington, Oregon, and California during the Pleistocene are now absent from these areas. This change is thought to be a result of climate shifts since deglaciation, particularly an increase in summer moisture deficits. While most Cladoniaceae species have reached a stable distribution, some are still in flux. Species like Cladina stellaris and Cladonia trasii appear to be continuing their southward expansion from northern glacial refugia.
Cladonia appalachiensis (endangered, 2020) growing on high-elevation Anakeesta Knob rock, faces threats from visitor disruption and changes in cloud cover and humidity. The species is particularly vulnerable due to its restricted range and specific habitat requirements. The main threats to Cladonia perforata (endangered, 2003) include habitat loss, , and improper fire management, with a single natural event potentially causing substantial subpopulation reduction.
| + IUCN-listed Cladoniaceae species | Cladonia perforata, endangered species since 2003 Cetradonia linearis - Flickr - pellaea.jpg | Cetradonia linearis Pilophorus fibula and Cetradonia linearis - Flickr - pellaea.jpg | Two rare species of Cladoniaceae together in the Great Smoky Mountains: Pilophorus fibula and C. linearis | |
Gymnoderma insulare (endangered, 2014), primarily found in old-growth forests in Japan and Taiwan, faces threats from natural hazards like and is affected by the decline of its tree hosts, Cryptomeria japonica and Chamaecyparis obtusa. The species' dependence on specific host trees and old-growth forest conditions makes it particularly vulnerable to forest degradation and climate change impacts.
On the red list of China's macrofungi, Cladonia delavayi (vulnerable), Cladonia pseudoevansii (critically endangered), Gymnoderma coccocarpum (endangered), and Gymnoderma insulare (endangered) are the representatives of the Cladoniaceae.
The complex net-like structures of the Australasian lichen Pulchrocladia retipora have been described as "of considerable beauty resembling lace or coral", and have been utilised in floral and architectural design. This species' branches, characterised by its numerous small holes, exemplify nature's efficient use of latticework structures. This design, widely used in construction for structures such as transmission towers or bridges, allows the organism to maintain structural integrity while minimising the amount of biological material used in its construction. The unique lichen architectures of five Cladoniaceae species are depicted in Ernst Haeckel's well-known and widely reproduced lichen-themed lithograph in his 1904 work Kunstformen der Nature ( The art forms of nature). According to the lichenologists Robert Lücking and Toby Spribille, "the Cladonia growth form continues to be one of the most widely recognized lichen architectures, with their basal scales and erect, often trumpet-shaped podetia".
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