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''Lopadium'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...
-forming
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
in the
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
family Lopadiaceae, which is in the order Lecideales. The genus contains 12 species. These lichens form thin, crust-like growths made up of fine granules or tiny scale-like flakes and produce small, stalkless disc-shaped reproductive structures that are distinctly narrowed at the base, giving them a pinched appearance. Distinguished by their unusual
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
-producing sacs that contain only a single large
ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...
instead of the typical eight, ''Lopadium'' species typically colonize decaying plant matter,
moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
cushions, or bark in cool, humid environments and can be identified microscopically by their unbranched
paraphyses Paraphyses are erect sterile filament-like support structures occurring among the reproductive apparatuses of fungi, ferns, bryophytes and some thallophytes. The singular form of the word is paraphysis. In certain fungi, they are part of the f ...
with distinctive dark brown swollen tips.


Taxonomy

''Lopadium'' was circumscribed by the German lichenologist Gustav Wilhelm Körber in 1855. He assigned '' Lopadium pezizoideum'' as the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
. The family
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
Lopadiaceae is classified in the order Lecideales. However, according to Alan Fryday and colleagues in the ''Revisions of British and Irish Lichens'' series, "It seems clear that Lopadiaceae does not belong in Lecideales but its true systematic position is unclear."


Description

''Lopadium'' forms a thin, crust-like
thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
that spreads across its
substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...
as a mosaic of fine granules or minute, scale-like flakes. A true protective is absent; instead, the surface is reinforced by a tough, cartilage-like layer. The lichen's algal partner () is a green, single-celled alga whose spherical to broadly
ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface;  that is, a Surface (mathemat ...
al cells provide
photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...
energy for the partnership. Reproductive bodies (
apothecia An ascocarp, or ascoma (: ascomata), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. As ...
) are small, stalkless that sit directly on the thallus but are distinctly narrowed at the base, giving each fruit body a pinched look. The rim projects beyond the disc, which ranges from shallowly concave to almost flat. Unlike many other lichens, this rim is constructed entirely of fungal tissue rather than incorporating thallus material. Internally, the apothecium is lined by a dark red-brown sheath of densely packed cells (the ). Between the spore-producing sacs are unbranched to sparsely forked threads called
paraphyses Paraphyses are erect sterile filament-like support structures occurring among the reproductive apparatuses of fungi, ferns, bryophytes and some thallophytes. The singular form of the word is paraphysis. In certain fungi, they are part of the f ...
; their tips swell into cone-shaped caps impregnated with dark brown pigment, a feature that helps separate Lopadium from look-alike genera. Each
ascus An ascus (; : asci) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some gen ...
(spore sac) contains a single, thick-walled
ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...
rather than the more usual eight. These spores are strongly —that is, they are divided by both lengthwise and crosswise walls so the interior resembles a tiny grid of bricks—and are initially colourless but may become slightly yellow-brown with age. Standard chemical spot tests and
thin-layer chromatography Thin-layer chromatography (TLC) is a chromatography technique that separates components in non-volatile mixtures. It is performed on a TLC plate made up of a non-reactive solid coated with a thin layer of adsorbent material. This is called the sta ...
have so far failed to detect any
lichen product Lichen products, also known as lichen substances, are organic compounds produced by a lichen. Specifically, they are secondary metabolites. Lichen products are represented in several different chemical classes, including terpenoids, orcinol deri ...
s. The genus usually colonises decaying plant matter,
moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
cushions or bark in cool, humid habitats, and can be distinguished from superficially similar genera by its combination of unbranched, cap-tipped paraphyses and the absence of chemical pigments such as
parietin Parietin is the predominant cortical pigment of lichens in the genus '' Caloplaca'', a secondary product of the lichen '' Xanthoria parietina'', and a pigment found in the roots of curled dock (''Rumex crispus''). It has an orange-yellow color ...
in the apothecia.


Species

,
Species Fungorum ''Index Fungorum'' is an international project to index all formal names (Binomial nomenclature, scientific names) in the fungus Kingdom (biology), kingdom. As of 2015, the project is based at the Royal Botanic Gardens, Kew, one of three partn ...
(in the
Catalogue of Life The Catalogue of Life (CoL) is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxono ...
) accepts 12 species of ''Lopadium'': *'' Lopadium brisbanense'' *'' Lopadium coralloideum'' *'' Lopadium cupuliferum'' *'' Lopadium disciforme'' *'' Lopadium hepaticicola'' *'' Lopadium heterosporum'' *'' Lopadium lecanorellum'' *'' Lopadium nigrum'' *'' Lopadium patwardhanii'' *'' Lopadium pezizoideum'' *'' Lopadium pulchrum'' *'' Lopadium subcoralloideum''


References

{{Taxonbar , from1=Q10569260 , from2=Q28872179 Lecideales Lichen genera Lecideales genera Taxa named by Gustav Wilhelm Körber Taxa described in 1855