How can cyanobacteria in contrast to saprotrophic bacteria

Notwithstanding that both Codes are incompatible, some have proposed to provide parallel classifications in each Code, while others proposed to adopt a modern unified code of nomenclature. Since the rearrangement of the classification along monophyletic lineages during the s, many clades now include a mixture of taxa from both Codes. Several taxa, such as diatoms, are described in parallel under both Codes with different names. This situation created and perpetuates anomalies, such as the recent redescription of the dictyostellid amoebae with the botanical Code Sheikh et al.

Issues such as these have been thoroughly discussed in the past Adl et al. It has been the responsibility of this committee to discuss and arbitrate published phylogenetic hypotheses, proposals for new names and name changes. Underlying these discussions are principles of nomenclatural priority in the spirit of the codes of nomenclature.

A classification is unlike a phylogenetic tree in a publication, where the discovery of new clades, branches, or robust nodes ultimately leads to proposing new names. Newly named clades and nodes have their utility in phylogenetic analysis and discussion, but do not need to be formalized in the classification immediately. An overwhelming number of spent names have thus accumulated, with an increasing frequency over the past four decades, most of which are no longer—or never were—in common use.

Many of these names were ephemeral, as their monophyly did not stand the test of time statistical analysis. The proliferation of these names reflects a methodological error practiced by some. As we argued before Adl et al. The task of refereeing and classifying falls on Society committees representing communities of professionals.

That is, however, too slow for the pace of changes today given the rate at which new information is becoming available. In contrast to a phylogenetic tree, a classification system belongs to a community of users, and it is generated through discussions of the available evidence, for pragmatic purposes of teaching, curation, organizing data, archiving and communicating with a common language. It is a commonly agreed point of reference. The Linnaean system that we have inherited has detailed codes of nomenclature that guide and regulate how living organisms are named, names changed and classified.

The elaborate rules arise from disputes and mistakes made in the past, in part out of respect for each other's work. Instead of providing a long list of rejected and invalid names, we can specify that those not selected in this classification were considered nomina ambigua, nomina perplexa, nomina dubia, nomina nuda or did not have nomenclatural priority and are declared nomina rejicienda.

Another proposed classification of prokaryotes and eukaryotes was published recently Ruggiero et al. This effort may be reasonable in their classification of the prokaryotes, but the eukaryote section does not pass standards of modern biology. Eukaryotes now form two Domains called Amorphea and Diaphoretickes, with several additional clades that do not group into a third Domain.

In the Amorphea, the Opisthokonta, Breviatea and Apusomonadida now form a robust clade, as noted earlier Adl et al. In addition, a sister clade to the Amorphea comprising several genera was recently described as CRuMs Brown et al. Genera at the base of each clade are amoeboid and phagotrophic. The Archaeplastida, Sar and several other clades remain a monophyletic clade under Diaphoretickes. The clade Cryptista comprising the cryptomonads, kathablepharids and Palpitomonas is well recognized and robust, although placement of its node within the Diaphoretickes remains problematic.

In some but not all analyses, the clade appears inside the Archaeplastida. This position has always occurred from time to time in some phylogenies with weak support, but there is now stronger support for this association. We are not committed to their inclusion within the Archaeplastida but do note its likelihood.

The inclusion of the Cryptista in the Archaeplastida would expand that group without affecting its defining criteria. Questioning the single origin of a plastid within the Archaeplastida is a rare minority opinion. The new robust support for the Cryptista clade is accompanied by a similarly robust support for a clade comprising the Centroplasthelida and Haptophyta as the Haptista within the Diaphoretickes.

Nodes at the base of the Alveolata are better resolved with additional genera. The placeholder name Protalveolata is no longer required. The Excavata comprise three clades: the Metamonada, the Discoba, and the Malawimonada. Their mutual relationships, as well as their relationships to other clades of eukaryotes, remain uncertain. The Excavates and several clades and genera fall outside of the two principal domains, but do not cluster together into a third domain.

This classification will serve as a primary starting reference for the taxonomic framework developed by UniEuk unieuk. The project will capture our collective knowledge on eukaryotic diversity, evolution, and ecology via three main modules EukRef, EukBank and EukMap. EukRef eukref. EukMap eukmap. It will be operational by and will allow registered community members to directly interact with and inform the taxonomic framework, and to flag taxonomy issues requiring revision.

As a whole, the UniEuk system will represent a community hub to centralize, standardize, and promote global knowledge on eukaryotic diversity, taxonomy and ecology. Several terms were clarified to correct misuse of terminology in publications. In , these were: eukaryote, prokaryote, algae, zoosporic fungi, protozoa, zooplankton, phytoplankton, cyst, spore and cilium. In , they were related to the cytoskeleton and motility: lobopodia, lamellipodia, filopodia, granuloreticulopodia, reticulopodia, axopodia, centriole, centrosome, microtubular organizing centre MTOC , basal body, kinetosome, kinetid and mastigont.

In this revision, they pertain to trophic functional groups. In addition to descriptions of morphology that accompany specimen, which is critical for understanding cell function and interpreting phylogenetic trees, improved descriptions of site and food preferences are required for an ecological interpretation of the role in the community and ecosystem.

Often species lack sufficient description of the collection site or feeding habit. To compare environmental DNA data sets, adequate metadata is necessary to select appropriate samples for comparison. Therefore, it is important that the environment and habitat is sufficiently described.

Merely stating marine, terrestrial or soil is grossly inadequate. It is also stratified through the profile, and across the diameter of each ped. Whether a soil or aquatic sample, solution chemistry and site physical parameters contribute to define the niche space. Because we care about nomenclature and the exact meaning of words and of names of things, especially species and their groupings into nodes and stems on phylogenetic trees, it is equally important to care for how we describe sampling sites and feeding habits.

There are two parts to describing the feeding habit: what is eaten and how it is eaten. Species that release enzymes extracellularly to digest substrates in their habitat, are generally called saprotrophic or lysotrophic , and contribute to the decomposition of organic matter. One incredible resource is FunGuild Nguyen et al.

Probably all eukaryotes are capable of osmotrophy, the acquisition of soluble nutrients through the cell membrane. For example, plants obtain their carbon for photosynthesis from the air, as well as some oxygen—however, they rely on osmotrophy through the roots to obtain all the other elements they need. Osmotrophy occurs through the ciliary pit, by pinocytosis, by diffusion, and by various membrane transport proteins.

Some species have no alternative form of acquiring energy, are very poor at decomposing substrates and are strict osmotrophs relying on dissolved nutrients. Detritus eaters ingest particles derived from cells and tissues, decomposing organic matter, starch granules, plant or animal debris, or wood microchip fragments. Species that eat other species are called consumers , and there are a variety of terms to describe the functional groups.

The size of particles filtered out of the liquid depend on the current generated, and the structure of the feeding apparatus Fenchel , and it is a good idea to specify what size prey are ingested.

The remaining consumers fall into two categories, the grazers and predators. Grazers , like a cow in a field of grasses, browse and ingest from surfaces covered with potential food items e.

Predators pursue scarce prey according to optimal foraging theory, typically handle one prey at a time, and it is mathematically distinct e. A popular term bacterivore has the unintended implication of voraciously devouring voracitas L. Use it, but be aware that some readers and reviewers will be more discriminating. In contrast, the more appropriate term —trophy trophe Gr. For species that ingest unicellular protists by phagotrophy, the correct term is cytotrophy.

Bacterium Ehrenberg has been the word used to refer to a prokaryotic cell, while cell Dutrochet ; Schleiden ; Schwann has been used since to refer to a eukaryotic cell. Mixotrophy refers to photosynthetic species that also ingest food by phagocytosis, and heterotrophs that retain prey plastids and symbionts. There are two distinct mechanisms to feed on algal filaments cellulosic cell wall or fungal hyphae chitinous cell wall.

One mechanism is to slurp the filaments like noodles and ingest them, and the other is to penetrate through the cell wall. Those that puncture through phagocytose cytoplasm, and some species even penetrate inside to ingest cytoplasm along the tube or in the spore. It is best to distinguish between the cell wall material to digest and the mechanism of ingestion. Thus, we have mycotrophy or phycotrophy , by either swallowing devoratis L.

Another poorly crafted term one encounters, albeit rarely, is eukaryovory. We have summarized the higher level classification of eukaryotes in Table 1 , with an estimate of the known number of genera, and providing informal phylum and class designations to help orient the student and users along the hierarchy, or nodes on a phylogenetic tree. The revised classification of eukaryotes is presented in Table 2 , and genera that have not been studied enough to place in the classification are listed in Table 3 as incertae sedis Eukarya.

Table 4 provides recommended primers for analysing DNA from environmental samples, noting that the choice of primers and depth of sequencing are important sources of variation between studies. Appendix S1 provides additional supporting literature that we considered important to understand the changes. Appendix S2 provides more detail about the trophic functional assignments across protists, by noting exceptions at the genus level.

Appendix S3 provides a standardized guide to East Asian users for the new terminology. Higher ranks of the eukaryotes suggesting the position of Linnaean ranks, and the number of known genera. Ochrophyta a. Chrysista C a Chrysophyceae O. Classification of the higher ranks of the protists and multicellular organisms. The authority to whom the taxon name is attributed appears immediately after the taxon name.

For purposes of nomenclature and stability of names in the classification, we have tried to retain the oldest term that correctly described the grouping, emended if necessary; in the square bracket following are inappropriate and incorrect names used in the literature, or that do not have nomenclatural priority. Adl et al. Selected references to the literature since can be found in Appendix S1.

Breviata , Lenisia , Pygsuia , Subulatomonas. Two groups are testate enclosed in a flexible or hard extracellular envelope with one to several opening s. Most only reported to be asexual, but sex and life cycles consistent with sex have been reported in all three major lineages—Tubulinea, Evosea and Discosea. Many taxa exhibit either sporocarpic 4 or sorocarpic 5 fruiting. Biciliated, uniciliated or multiciliated stages in the life cycle of some taxa; some taxa exhibit reduction of the bikont kinetid to a unikont kinetid.

Organisms producing lobose pseudopodia lobopodia 9. If cells are flattened or branched they are capable of altering the locomotive form from a flattened, expanded one to monopodial or polypodial, with subcylindrical pseudopodia. Monoaxial flow of the cytoplasm in every pseudopodium or in the entire cell. No convincing evidence of ciliate stages Two groups are testate, and two sorocarpic taxa are known.

No sporocarpy has been reported. The least inclusive clade containing Amphizonella sp. The least inclusive clade containing Vermamoeba vermiformis, Echinamoeba silvestris and Micriamoeba tesseris.

Echinamoeba, Micriamoeba , Vermamoeba. Cells naked or covered with a hard test; tubular or produce tubular pseudopodia; if flattened or branched, capable of altering the locomotive form to monopodial or polypodial, with tubular pseudopodia.

The least inclusive clade containing Amoeba proteus, Arcella intermedia and Rhizamoeba saxonica. Naked amoebae with locomotive form altering from a flattened expanded or reticulate one to a subcylindrical monopodial one when in rapid movement or under specific conditions; adhesive uroidal structures always present. Test proteinaceous, with calcified inner layer, or completely chitinoid with recycled mineral or organic particles; pseudopodia conical, pointed, consist solely of the hyaloplasm, sometimes branched and may anastomose.

Naked amoebae with tubular, subcylindrical pseudopodia or the entire cell is monopodial and subcylindrical ; no alteration of the locomotive form; no adhesive uroidal structures; sorocarpic development in some species. Representatives of this clade can vary across almost the entire range of morphologies seen in Amoebozoa. Many members have complex life cycles 15 that include amoeboid, ciliated and fruiting stages.

Some species appear to be exclusively ciliated with no amoeboid features. Most taxa with only a subset of these life cycle stages. The least inclusive clade containing Physarum polycephalum Eumycetozoa , Protostelium nocturnum Variosea , Squamamoeba japonica Cutosea , and Entamoeba histolytica Archamoebea. Amoebae elongated or flabellate during locomotion and sometimes branched to reticulate, with long, pointed, often branching and occasionally anastomosing subpseudopodia; ciliated cells may be the sole state , or present as ciliated amoebaes, or be one state in a life cycle that also includes obligate amoebae; the kinetid of ciliates bikont or unikont, associated at least with one cone of microtubules; several taxa contain a sporocarp state.

The least inclusive clade containing Flamella balnearia, Protostelium nocturnum, Acramoeba dendroida and Phalansterium solitaruium. The least inclusive clade containing Flamella aegyptia and Telaepolella tubasferens. Flamella, Telaepolella. The least inclusive clade containing Filamoeba nolandi and F. Heliamoeba mirabilis. The least inclusive clade containing Protostelium nocturnum and Protostelium mycophaga.

Protostelium Uninucleate, flabellate to branching amoebae; several members sporocarpic, one species with ciliated amoebae and obligate amoebae. The least inclusive clade containing Soliformovum irregularis, Nematostelium gracile and Acramoeba dendroida.

Acramoebidae, Schizoplasmodiidae, Soliformoviidae. Uninucleate amoebae, flattened highly branched, with very slender, pointed, sometimes branched hyaline subpseudopodia never forming a network; ciliated stages unknown. Acramoeba dendroida. The least inclusive clade containing Ceratiomyxella tahitiensis, Nematostelium ovatum, Schizoplasmodium cavostelioides. Ceratiomyxella, Nematostelium, Schizoplasmodium. The least inclusive clade containing Soliformovum irregularis and Grellamoeba robusta.

Grellamoeba , Soliformovum. The least inclusive clade containing Angulamoeba microcystivorans and A. Sporocarpic group with various types of amoebae, from uninucleate amoebae to multinucleate reticulate plasmodia, all characterized by producing long, filose, subspeudopodia, anastomosing in some taxa; one taxon with ciliated amoebae and obligate amoeba with possible sex in the life cycle; ciliated amoebae possesses one to several, reduced unikont kinetids per cell, not associated with the nucleus; species without ciliated amoebae have akinetid amoebae that germinate from spores; sporocarps in all species with single, nondeciduous spores; morphology variable and taxon specific; spores of all species displaying some type of sculpturing; cysts of some species displaying sculpturing as well.

Cavostelium, Schizoplasmodiopsis, Tychosporium. The least inclusive clade containing Ischnamoeba montana and Ischnamoeba sp. Multinucleate, highly branching and reticulate amoebae with slender, pointed, sometimes branched and anastomosing pseudopodia; the whole cell body is strongly branching and narrow, especially in the most extended parts, while more condensed parts are wider; posterior end usually pointed with no or few pseudopodia and no branching; many contractile vacuoles present; movement very slow; ciliated stages unknown.

The least inclusive clade containing Darbyshirella terrestris and Darbyshirella sp. Rounded cells with multiple radiating projections, which may be cilia arising from the solitary kinetosomes.

Multinucleate, highly branching and reticulate naked amoebae with slender, pointed, sometimes branched pseudopodia; movement of entire cells very slow; the main cell body is multiply branched and anastomosing, and can grow into giant networks up to several mm with intersecting segments of varying width and numerous terminal branching areas; abundant fine pseudopodia are concentrated mostly at the extremity of lateral and terminal branches, especially in complex networks, but can be formed anywhere around the cell body in simpler forms; ciliated stages unknown.

Dictyamoeba vorax. Arboramoeba reticulata. Uniciliate sedentary cells, colonial or solitary; cilium arises from the apical part of the cell; one centriole per kinetid; ciliary pocket usually surrounded by a collar; some species form short tapering cytoplasmic projections and move over the substratum using the conformation of their body or producing cytoplasmic eruptions.

The least inclusive clade containing Phalansterium solitarium and P. The least inclusive clade containing Dictyostelium discoideum, Physarum polycephalum and Ceratiomyxa fruticulosa. One species known to lack plasmodial state and one species known to lack ciliated amoebae.

Containing taxa predominantly with dark coloured spores, in mass. Exclusively fruiting, with microscopic protosteloid sporocarps with a microscopic stalk with one to four, sometimes more, spores; life cycle with ciliated amoebae stage with rootlets as Eumycetozoa with rootlet 3 consisting of a band of only two microtubules; giving rise to a uninucleate to plurinucleate obligate amoeba that develops into one or more sporocarps; prespore cells site of meiotic prophase and meiosis completed in spore complement.

Clastostelium, Protosporangium. With ciliated amoebaes developing from cleavage of germling from a tetranucleate spore; obligate amoeba is multinucleate plasmodium secreting an extracellular slime mound or columns upon which it cleaves into single uninucleate prespore cells that individually develop into a stalked sporocarp bearing a single, tetranucleate spore.

Armaparvus, Sapocribrum, Squamamoeba. Ciliated amoebaes or amoeboid organisms without cilia. The single motile anterior cilium, when present, associated with microtubular cone connected to the nucleus.

Ciliated amoebaes with hyaline lateral pseudopodia. Pelomyxa, Mastigella. Ciliated amoebaes with single immobile cilium, microtubular cone associated with nucleus, when several nuclei present, each nucleus is connected to its own microtubular cone; with rhizostyle, derived from the lateral microtubular root. Cilia and kinetosomes absent; with mitosomes instead of classical mitochondria; peroxisomes absent; mitosis closed with endonuclear centrosome and spindle; reduced Golgi dictyosome.

Ciliate ciliated, possessing a rhizostyle arising from the basal body of the cilium and probably derived from the microtubular cone. Flattened naked amoebae, never producing tubular, subcylindrical pseudopodia and never altering the locomotive form to the tubular, subcylindrical one; cytoplasmic flow polyaxial or without a pronounced axis; ciliated stages unknown; several taxa sporocarpic.

Sappinia, Stenamoeba, Stratorugosa, Thecamoeba. Dermamoeba, Mayorella, Paradermamoeba. Flattened lingulate amoebae without differentiated glycocalyx; with complex life cycle where active cells transform into coccoid stages, which undergo subsequent buddings, eventually turning into ramified structures pseudomycelia with spherical cysts in a terminal position on the ramifications; these pseudomycelia disappear and cysts are released prior to germinating into active trophozoites.

Mycamoeba gemmipara. Locomotive form mostly has a shape of an irregular triangle with basement directed forward; wide anterior hyaloplasm; fibrous axial cores both in dactylopodia and in the floating pseudopodia. Stygamoeba, Vermistella. MTOC located near the dictyosome; several taxa with protosteloid sporocarpy. The least inclusive clade containing Pellita catalonica, Gocevia fonbrunei, Endostelium zonatum, Acanthamoeba castellanii.

Flattened with prominent subpseudopodia, flexible and tapering to a fine tip and sometimes furcated near their base acanthopodia ; without adhesive uroid; trilaminate MTOC; some species in culture appear as a branched, flattened sheet; at least two taxa, Acanthamoeba and Luapeleamoeba, contain species with protosteloid sporocarpy.

Thick cell coat envelops the entire cell with the exception of subpseudopodial tips and is integrated with plasma membrane, or is located on the dorsal surface only, and is loosely attached to the plasma membrane; MTOC, when known, trilaminate.

One genus, Endostelium, with several protosteloid sporocarpic species. Cochliopodium , Ovalopodium, Parvamoeba. Single posterior cilium without mastigonemes, present in at least one life cycle stage or secondarily lost; with a pair of kinetosomes or centrioles, sometimes modified; flat rarely tubular mitochondrial cristae in the unicellular stage. The primary reference phylogenies are Carr et al.

Incertae sedis Holozoa:. Spherical single cells 4. Predominantly unicellular, roundish uniciliated motile swimming cells; cilium emerges from the middle lateral point of the cell, ended by short acroneme and directs backward; cells naked; cells can form clusters of multiple cells; predatory phagotroph of heterotrophic chrysomonads and bodonids; life cycle includes unicilaited roundish motile swimming cells, ciliated amoeboid cells, amoeboid aciliated cells with filopodia and spherical cysts; known from freshwater.

Syssomonas multiforma. Amphibiocystidium ranae, Amphibiothecum penneri, Chromosphaera perkinsii, Dermocystidium, Rhinosporidium seeberi, Sphaerothecum destruens.

Abeoforma whisleri, Amoebidium parasiticum, Anurofeca richardsi, Astreptonema, Caullerya mesnili, Creolimax fragrantissima, Eccrinidus flexilis, Enterobryus oxidi, Enteropogon sexuale, Ichthyophonus, Palavascia patagonica, Pseudoperkinsus tapetis, Psorospermium haeckeli, Sphaeroforma arctica; S. Trophic cells naked, unicellular; uninucleate; aerobic with flat mitochondrial cristae; long nontapering tentacles supported by microfilaments, unlike collar in choanoflagellates; phagotrophic.

Capsaspora, filose amoeba with cystic and aggregative stages; Ministeria and Pigoraptor with cilium, Ministeria is not motile but uses a stalk attached to the substrate; Pigoraptor, ciliated amoeba and predator, as Capsaspora it can present pluricellular clusters.

Capsaspora, Ministeria, Pigoraptor. Nitsche et al. Extracellular glycocalyx or theca that is entirely organic and does not project above the anterior end of the extended feeding cell; vegetative stage usually sedentary and stalked; brief motile stage for dispersal. Type genus: Acanthoeca Ellis Recognized genera: Acanthoeca, Helgoeca , Polyoeca , Savillea. Type genus: Stephanoeca Ellis Reproduction sexual through an egg cell, fertilized usually by a monociliated sperm cell with acrosome; embryonic development with blastula followed by gastrulation that begins the differentiation into endoderm, ectoderm, mesoderm, and neuroderm; tissues organized into organs that share tasks for the individual, unless secondarily lost; some secondarily reduced to small number of cells e.

Subdivisions beyond Porifera and Trichoplax not shown. Flat mitochondrial cristae; sexual species, zygotes forming larva nine known larval types or juveniles; asexual reproduction by gemmules, budding or fragmentation; sessile adult; differentiation of larva to a variety of cell types, including choanocytes, amoeboid cells and cells with granular inclusions; cell types transformable into other types as necessary; cells more or less independent; without mesoderm, nervous tissue, desmosomes, localized gonad or glandular digestive cells.

Exclusively marine, and especially in the deep sea; siliceous spicules triaxonic, hexactinic; square axial proteinaceous filament in spicules, whole sponge formed by a single continuous multinucleate syncytium, with some differentiated cells; electrical conductance across body; reproduction when known is viviparous with a trichimella larvae. Hexaster spicules.

Verongimorpha and Keratosa do not have for the most part siliceous spicules, Heteroscleromorpha have a high diversity of siliceous spicules; spicules differentiated in meglascleres and microscleres, triangular axial proteinaceous filament in spicules; larva with outer ciliated cells; one family Cladorhizidae with extracellular digestion, by amoeboid cell aggregation of captured crustacean prey; one order Spongillida living in freshwater.

Mostly with spongin skeleton, otherwise with siliceous spicules Chondrilla , or no skeleton at all. Synapomorphies include the following ultrastructure characters: orientation of accessory centriole, the nuclear apex, the Golgi apparatus and similarities in embryonic development.

Demospongiae with a skeleton made of spongin fibre; spongin fibres are either homogenous or pithed and strongly laminated with pith grading into bark. One genus has a hypercalcified basal skeleton Vaceletia. Dendroceratida Minchin ; Dictyoceratida Minchin, Exclusively marine, from shallow depths to the deep sea; siliceous spicules or no spicules at all, tetraxonic, not differentiated between megascleres and microscleres, without defined axial proteinaceous filament in spicules only observed in one species ; true epithelium; hermaphroditic; viviparous cinctoblastula larva.

Homosclerophorida Dendy, Exclusively marine, from shallow depths to the deep sea; calcium carbonate spicules; viviparous, hermaphrodites. Unambiguous characters congruent with molecular phylogenies unclear. Larva amphiblastula. Clathrinida Hartman, ; Murrayonida Vacelet Larva calciblastula; hermaphroditic. Leucosolenida Hartman ; Lithonida Vacelet Trichoplax adhaerens.

Holomycota Liu et al. The primary reference is Brown et al. Additional phylogenies are Brown et al. Thallus monocentric, epibiotic, penetrates host wall with rhizoid in parasitic species; amoeboid zoospores with posterior pseudocilium; sporangia as in Rhizophydiales Chytridiomycetes ; sexual reproduction not observed. Some sorocarpic, e. Fonticula, Nuclearia, Parvularia. Moore Faust , Batrachochytrium dendrobatidis Longcore, Pessier and D.

Nichols , Allomyces arbusculus E. Le Monn , Rhizophagus intraradices N. Schenck and G. Walker and A. Probably more than ten distinct major lineages of fungi within the ascomycetes are lichenised. Current estimates suggest that one fifth of all known fungi and half of all ascomycetes are lichenised, with about 28, species worldwide. As with most organisms, lichen fungi are most diverse and least studied in the tropics.

For example, the genus Arthonia is comprised of a mix of lichenised and non-lichenised species and includes many which are specialist parasites, only found on one or a few closely-related host lichens.

In a single genus, then, we have a case of lichen parasites evolving from lichen fungi! Other non-lichen fungi arose from lichenised ancestors, such as Stictis and Ostropa. Fungi are classified in part by the type of spore-producing structures they produce, with the cup fungi ascomycetes named for the open, cup-shaped structures which often bear the sexual spores of the fungi.

Not all ascomycetes have these cup-shaped structures, however, and, easily observed morphological characteristics like fruit type cup-like apothecia versus flask-shaped perithecia, for example cannot always be used to assess relationships. Unfortunately, this means that not all fungi sharing a single characteristic are likely to be related.

However, some order can be distilled. The bulk of lichen diversity belongs to the class including the well-known genera Lecanora , Cladonia , Parmelia and Peltigera Lecanoromycetes, or the Lecanora -group , where spores are borne mostly in open or cup-shaped fruits apothecia. This group of fungi is very old, estimated to have evolved during the Carboniferous period.

The very first lichens probably date back to before the origin of land plants, when most of the biodiversity of Earth was in the sea. Many Arthonia relatives also have open cup type fruits, but their development is quite different, giving a clue that they are not closely related to the Lecanora -group. Instead, they are more closely related to other ascomycetes that have flask-shaped spore-bearing structures perithecia.

Similarly, for still other lichen groups, morphological similarities have been confirmed by molecular evidence to point to their widely disparate origins in the ascomycete tree of life. For examples of these, students would be advised to visit the tropics, where the members of the Arthonia -, Trypethelium - and Pyrenula - groups form conspicuous and sometimes colourful crusts. In Britain, the smooth barked trees of the western districts are good places to see some of our Arthonia and Pyrenula species.

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