Peltula | |
---|---|
Peltula euploca | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Lichinomycetes |
Order: | Lichinales |
Family: | Peltulaceae Büdel (1986) |
Genus: | Peltula Nyl. (1853) |
Type species | |
Peltula radicata Nyl. (1853) | |
Synonyms [1] | |
Peltula is a genus of small dark brown to olive or dark grey squamulose lichens. These lichens typically grow on rocks in arid and semi-arid environments worldwide. They consist of a fungus living in symbiosis with a photosynthetic partner, specifically a cyanobacterium of the genus Chroococcidiopsis . Peltula is the only genus in the family Peltulaceae, [5] which belongs to the Lichinomycetes, a class of fungi that form lichens. The genus includes about 50 recognised species, which exhibit a variety of growth forms ranging from flat and crust-like to more complex, leaf-like structures. Peltula lichens play important ecological roles in harsh environments, contributing to soil stability and nutrient cycling.
To cope with their challenging habitats, Peltula species have evolved various adaptations. These include specialised protective layers and the ability to withstand both drought and flooding. The thalli of Peltula lichens are typically small, with a stratified structure consisting of an upper epinecral layer , a photobiont layer , a medulla, and usually a lower cortex . Peltulaceae generally lack secondary metabolites, which distinguishes them from many other lichen families. The genus has a cosmopolitan distribution, with members found across various continents, occupying diverse substrates including rocks, soil, and occasionally tree bark. Molecular phylogenetics studies have significantly altered the classification of these lichens. Formerly separate genera are now incorporated into Peltula, rendering Peltulaceae a monogeneric family.
Genus Peltula was circumscribed by the Finnish lichenologist William Nylander in 1853. He assigned the desert soil lichen Peltula radicata as the type, and at that time, only species. In his original description of Peltula radicata, Nylander characterised it as having a rust-brown, peltate thallus measuring at least 3 mm wide, with an irregularly and sparsely grooved surface. He noted that the thallus had a centrally depressed, umbilicate attachment, fixed to the substrate by a few pale, long, and strong rhizines. Nylander described the apothecia as disc-shaped and the same colour as the thallus, initially almost endocarpoid, but expanding significantly with age and featuring a depressed thalline margin. He observed that the asci contained numerous spores, 8–48 or possibly more. The type (biology) was found growing on sandy soil near Biskra, Algeria, alongside Lecanora endocarpa . In establishing the new genus Peltula, he distinguished it from other Lecanorine genera by its thallus being attached below with long, central rhizines. [6] In 1890, Vainio proposed that Peltula should be considered a section of the genus Heppia rather than an independent genus. [7]
For decades, the genus Peltula saw limited use. Many species now classified under Peltula were previously placed in Heppia . [8] Vilmos Kőfaragó-Gyelnik added some species to Peltula in 1935. [9] The family was Peltulaceae proposed by the German lichenologist Burkhard Büdel in 1986. [10] He identified four types of growth morphologies in the family: leaf-like, squamulose, crustose and fruticose. [11] The genera Phyllopeltula and Neoheppia were created as segregates of Peltula to contain species with differences in their cortex morphology and substratum. Neoheppia was introduced by Alexander Zahlbruckner in 1909 for N. brasiliensis, which had a crustose thallus attached to its substrate by all parts of its lower surface. [2] Phyllopeltula differed from the typical Peltula morphology with subfoliose-compound thalli. [4] These genera were included as part of the Peltulaceae. [12] [4]
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Cladogram showing the phylogeny of some species in the family Peltulaceae, based on analysis by Kauff et al. in 2018. |
Egea (1989) and Büdel (1987) made early attempts to establish phylogenetic lineages within Peltula based on morphology. [13] [14] Egea identified two major evolutionary lineages based primarily on substratum fixation, while Büdel described two groups of closely related species based on thallus morphology. However, these classification attempts remained controversial due to the morphological variability within the genus. [15]
Early molecular phylogenetics work (2001) showed that the family was monophyletic. [16] More recent molecular studies have led to a significant revision of the family's taxonomy. A comprehensive study by Kauff and colleagues (2018) analysed six genetic loci from 37 of the 47 species classified within Peltulaceae at the time. The results of this analysis revealed that Phyllopeltula and Neoheppia are not monophyletic and are nested within the genus Peltula. As a consequence of these findings, Phyllopeltula and Neoheppia have been subsumed into Peltula, making Peltulaceae a monogeneric (single-genus) family. The family now includes about 50 recognised species, all within the genus Peltula. The study also highlighted significant challenges in species delimitation within Peltula. Traditional morphological characters, such as growth forms and thallus anatomy, which were previously used to delimit genera and species within the family, have been shown to be unreliable indicators of phylogenetic relationships. Significant differences in thallus shape and structure were seen within several species, further complicating classification efforts based on morphology alone. [15]
The genus name is derived from the Latin pelta, 'small shield', alluding to the shape of the squamules. [17] In North America, the colloquial name "rock olives" refers to members of this genus, highlighting both their colour and typical substrate. Several North American species with common names include the cylindrical, powdery, common, stuffed, and giant rock-olives. [18]
Peltulaceae members exhibit a diverse range of thallus morphologies. Thalli are typically small, ranging from minute squamules to larger compound structures. Most species possess a stratified ( heteromerous ) thallus structure, consisting of an upper epinecral layer , a photobiont layer , a medulla, and usually a distinct lower cortex . The epinecral layer, often yellowish to brown, provides protection and its development is influenced by light intensity. The medulla in many species contains air spaces of various sizes, while some taxa lack a lower cortex or medullary cavities. [15]
The growth forms of Peltulaceae can be categorised into six types based on morphology and anatomy. Peltate-umbilicate forms are often singular thalli, rarely compound, attached by an umbilicus or central strand of hyphae. Squamulose-semifruticose forms are characterised by large medullary cavities. Squamulose-compound forms are rarely singular. Subfoliose, compound forms lack medullary cavities and a lower cortex. Crustose- areolate forms have no medullary cavities or lower cortex, but possess a deeply penetrating cyanobiont layer. Finally, a unique crustose form is found in P. inversa, which exhibits an inverse thallus anatomy. [15]
Peltulaceae are exclusively associated with unicellular cyanobacterial photobionts, predominantly of the genus Chroococcidiopsis . Apothecia are common in most species, with a few exceptions, [15] and they are zeorine in form and typically immersed in the thallus. [19] The family is characterised by uniform reproductive structures across all species, including polysporous asci with a distinctive gelatinous sheath, and simple , single-celled, colourless spores. [15] The ascospores range in shape from more or less spherical, to ellipsoidal, to bacilliform , and measure 3–12 by 2–6 μm. [17] The asci are unitunicate - rostrate , which means have they a single-layered wall with a beak-like tip. [19] Pycnidia, conidiophores, and pycnospores are also consistent in structure throughout the family; [15] the conidia are htaline, oval to fusiform in shape, and have dimensions of 1.5–4.3 by 0.5–2.5 μm. Vegetative reproductive structures such as soredia and isidia occur in a small number of species. [15]
Unlike many other lichen families, Peltulaceae generally lack secondary metabolites (lichen products). An exception is Peltula langei , which produces a yellow pigment similar to myeloconon C. [15] The thallus structure of Peltulaceae species shows various adaptations to their predominantly arid and semi-arid habitats. [20] The epinecral layer shields the photobiont from intense sunlight, while different growth forms are associated with varying water availability. Some species, particularly those with squamulose to semifruticose thalli and large medullary cavities, are adapted to temporarily inundated habitats. These morphological and anatomical features reflect the family's successful adaptation to challenging environmental conditions, allowing them to grow in a range of ecological niches from desert rocks to occasionally submerged surfaces. [15]
The Peltulaceae has a cosmopolitan distribution, with members found across various continents. These lichens are particularly well-adapted to arid and semi-arid environments, where they play important ecological roles. Despite their preference for dry habitats, some species have been documented in areas with more moderate climates, including locations as far north as Sweden and as easterly as the Baikal region of Siberia. [15]
Peltulaceae species occupy a diverse array of substrates. Many members of the family are saxicolous, growing on rock surfaces. These rock-dwelling species can be found on various geological formations, from exposed cliff faces to small stones. Some Peltulaceae have evolved to grow on soil, while others, such as Peltula corticola , have adapted to a corticolous lifestyle, growing on tree bark. In an example of niche specialisation, P. inversa exhibits a hypolithic habit, growing on the underside of quartz rocks. [15] In India, burnt clay tiles, commonly used for roofing, support both Peltula euploca and P. patellata. Under constant sun exposure for most of the day, the lichens develop a thickened upper cortex that both helps to retain moisture and acts as a photoprotectant. [21]
The family's adaptability is further exemplified by the range of specific microhabitats they occupy. Some species prefer inclined rock surfaces, while others colonise flat rock expanses. Certain Peltulaceae species have developed the ability to withstand periodic inundation, allowing them to inhabit seepage areas on rocks that are occasionally flooded. This diverse range of habitats reflects the family's evolutionary success in colonising challenging environments. [15]
The morphological and anatomical features of Peltulaceae species often correspond to their specific environmental conditions. For instance, the development of the epinecral layer , which provides protection to the photobiont, is influenced by the intensity of light in the habitat. The various growth forms observed in the family, from peltate to crustose, are closely linked to water availability in their respective environments. Species that experience occasional submersion often possess large medullary cavities, an adaptation that likely aids in gas exchange and water relations during both dry and inundated periods. [15]
The habitat preferences and adaptations underscore the ecological importance of Peltulaceae in arid and semi-arid ecosystems. As primary producers in these often-sparse environments, they contribute to soil stability, nutrient cycling, and provide microhabitats for other organisms, playing a role in the biodiversity of challenging climatic regions. [15]
Five species of Peltula are known to occur in India. [22] About 20 species have been recorded in China, [8] and 18 from North America north of Mexico. [23] Fifteen species occur in Australia, [17] and eleven species were reported to occur in East Africa. [24]
As of September 2024 [update] , Species Fungorum (in the Catalogue of Life) accepts 35 species in Peltula, [25] although 66 unique species names have been proposed in the genus.
Peltula langeiBüdel & Elix (1997), a Western Australian species described as new in 1997, [42] was not validly published. [43] The original binomial for Peltula oleifera(H.Magn.) J.C.Wei (1991) (Heppia oleifera H.Magn.) had already been reduced to synonymy with Peltula impressula in 1981, [44] a decade before Wei erroneously proposed a transfer to Peltula. [45]
The Lichinaceae are a family of ascomycete fungi. Most species are lichenized with cyanobacteria, and have a distribution largely in temperate regions.
Ramalina is a genus of greenish fruticose lichens that grow in the form of flattened, strap-like branches. Members of the genus are commonly called strap lichens or cartilage lichens. Apothecia are lecanorine.
Lempholemma is a genus of lichen-forming fungi in the family Lichinaceae.
Lichinella is a genus of lichen-forming fungi in the family Lichinaceae. It was circumscribed in 1872 by Finnish lichenologist William Nylander. Five species are accepted by Species Fungorum.
Peccania is a genus of lichenized fungi within the family Lichinaceae. As of July 2023, Species Fungorum accepts five species of Peccania, although many more species have been placed in the genus.
Pterygiopsis is a genus of fungi within the family Lichinaceae. It contains 11 species.
Crustose lichens are lichens that form a crust which strongly adheres to the substrate, making separation from the substrate impossible without destruction. The basic structure of crustose lichens consists of a cortex layer, an algal layer, and a medulla. The upper cortex layer is differentiated and is usually pigmented. The algal layer lies beneath the cortex. The medulla fastens the lichen to the substrate and is made up of fungal hyphae. The surface of crustose lichens is characterized by branching cracks that periodically close in response to climatic variations such as alternate wetting and drying regimes.
Heppia is a genus of olive, brownish, gray, or blackish squamulose, crustose, or peltate like lichens. Heppia was once the type genus of the family Heppiaceae, but that family was folded into synonymy with Lichinaceae.
Athallia is a genus of lichen-forming fungi in the family Teloschistaceae. It was circumscribed in 2013 by Ulf Arup, Patrik Frödén, and Ulrik Søchting, and the type species is Athallia holocarpa. The genus name means "without a thallus".
Schaereria is a genus of lichen-forming fungi. It is the sole genus in the family Schaereriaceae, which itself is the only family in the Schaereriales, an order in the subclass Ostropomycetidae of the class Lecanoromycetes. Most Schaereria species are crustose lichens that live on rocks. Schaereria was first proposed by Gustav Wilhelm Körber in 1855 and was later taken up by other lichenologists despite periods of disuse.
Heppia arenacea is a species of terricolous (ground-dwelling) lichen in the family Lichinaceae. Discovered in Yemen, it is characterized by its sand-coloured thallus and the incorporation of soil particles throughout its vegetative parts. The lichen is found in soil crust communities over limestone and basaltic rock in desert habitats, as well as in partially sheltered areas between large boulders.
Pseudoheppia is a fungal genus in the family Lichinaceae. It contains a single species, Pseudoheppia schuleri, a saxicolous (rock-dwelling) squamulose lichen.
Gloeoheppia is a genus of lichen-forming fungi in the family Gloeoheppiaceae. It comprises five species. The genus is distinguished from similar-looking lichens like Heppia by its internal structure, the nature of its photobiont, and details of its reproductive structures.
Pseudopeltula is a genus of lichen-forming fungi in the family Gloeoheppiaceae. Established in 1995 by the lichenologist Aino Henssen, the genus currently includes four recognised species. These small cyanolichens are characterised by their squamulose (scaly) to peltate (shield-shaped) thalli, which lack a lower cortex and are attached to the substrate by rhizines. A key feature of Pseudopeltula is its complex apothecia, which have hymenia that often become divided by sterile tissue as they mature. The genus is primarily found in arid and semi-arid regions of North America, Mexico, and the Caribbean, where species typically grow on soil, rock, or thin soil over rock, often forming part of biological soil crusts in desert environments.
Eschatogonia is a genus of lichen-forming fungi in the family Ramalinaceae. It has seven species. The genus was circumscribed by the Italian lichenologist Vittore Benedetto Antonio Trevisan de Saint-Léon in 1853.
Peltula lobulata is a species of saxicolous (rock-dwelling), squamulose lichen that belongs to the family Peltulaceae. This species was first described in 2019 following its discovery in Beijing, China.
Peltula polycarpa is a species of saxicolous (rock-dwelling), squamulose lichen in the family Peltulaceae. First described in 2022, it is endemic to Beijing's Mentougou District in China.
Peltula polyphylla is a ground-dwelling, squamulose lichen species in the family Peltulaceae, characterised by its distinctive multi-lobed structure. Found in China, it was described as a new species in 2022.
Peltula pseudoboletiformis is a species of saxicolous (rock-dwelling), squamulose lichen lichen in the family Peltulaceae, described in 2022. It is noted for its resemblance in thallus structure to the mushroom-forming fungal genus Boletus, which is reflected in its name.
Peltula submarginata is a species of saxicolous (rock-dwelling), squamulose lichen in the family Peltulaceae, first described in 2022. It occurs in China.
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