Incertae sedis (Latin for 'of uncertain placement')[2] orproblematica is a term used for ataxonomic group whose broader relationships are unknown or undefined.[3] Alternatively, such groups are frequently referred to as "enigmatic taxa".[4] In the system ofopen nomenclature, uncertainty at specific taxonomic levels is indicated byincertae familiae (of uncertain family),incerti subordinis (of uncertain suborder),incerti ordinis (of uncertain order) and similar terms.[5]
The fossil plantParadinandra suecica could not be assigned to any family, but was placedincertae sedis within the orderEricales when described in 2001.[6]
The fossilGluteus minimus, described in 1975, could not be assigned to any known animalphylum.[7] The genus is thereforeincertae sedis within the kingdomAnimalia.
While it was unclear to which order theNew World vultures (family Cathartidae) should be assigned, they were placed in Avesincertae sedis.[8] It was later agreed to place them in a separate order, Cathartiformes.[9]
Bocage's longbill,Motacilla bocagii, previously known asAmaurocichla bocagii, is a species ofpasserine bird that belongs to the superfamilyPasseroidea. Since it was unclear to which family it belongs, it was classified as Passeroideaincertae sedis, until a 2015 phylogenetic study placed it inMotacilla ofMotacillidae.[10][11]
Biological dark matter, genetic material produced from unidentified microorganisms that appears to match no known species. LikeParakaryon, its producers' positions in the tree of life are completely unknown.
Metallogenium is a bacterium that can form star-shaped minerals.[13]
Circothecidae are a family ofCambrian animals, sometimes attributed to theHyolitha, though some authors suggest (on the basis of no specified evidence) that they are definitely not.
Thefrosted phoenix moth (Titanomis sisyrota) is so rare and so obscure it is unable to be placed in any family within theLepidoptera.
When formally naming a taxon, uncertainty about its taxonomic classification can be problematic. TheInternational Code of Nomenclature for algae, fungi, and plants, stipulates that "species and subdivisions of genera must be assigned to genera, and infraspecific taxa must be assigned to species, because their names are combinations", but ranks higher than thegenus may be assignedincertae sedis.[15]
...the removal of many genera from new and existing families into a state of incertae sedis. Their reduced status was attributed largely to poor or inadequate descriptions but it was accepted that some of the vagueness in the analysis was due to insufficient character states. It is also evident that a proportion of the characters used in the analysis, or their given states for particular taxa, were inappropriate or invalid. Additional complexity, and factors that have misled earlier authorities, are intrusion by extensivehomoplasies, apparent character state reversals andconvergent evolution.
If a formalphylogenetic analysis is conducted that does not include a certain taxon, the authors might choose to label the taxonincertae sedis instead of guessing its placement. This is particularly common whenmolecular phylogenies are generated, since tissue for many rare organisms is hard to obtain. It is also a common scenario whenfossil taxa are included, since many fossils are defined based on partial information. For example, if the phylogeny was constructed using soft tissue andvertebrae as principal characters and the taxon in question is only known from a single tooth, it would be necessary to label itincertae sedis.[5]
If conflicting results exist or if there is not a consensus among researchers as to how a taxon relates to other organisms, it may be listed asincertae sedis until the conflict is resolved.[5]
The termincertae sedis refers to uncertainty about phylogenetic position of a taxon, which may be expressed, among others, by using a question mark after or before a taxon name. This should be distinguished from the situation where either it is uncertain how to use a name, often because the types have been lost (nomen dubium,species inquirenda), or whether a poorly preserved specimen should be included within a given species or genus, which is often expressed using a 'cf.' (from Latinconfer, compare, before a taxon name); such a convention is especially widespread in palaeontology.[17]
In zoological nomenclature, "incertae sedis" is not a nomenclatural term at allper se, but is used by taxonomists in their classifications to mean "of uncertain taxonomic position".[2]Glossary In botany, a name is not validly published if it is not accepted by the author in the same publication.[15]Article 36.1 In zoology, a name proposed conditionally may beavailable under certain conditions.[2]Articles 11 and 15 For uncertainties at lower levels, some authors have proposed a system of "open nomenclature", suggesting that question marks be used to denote a questionable assignment.[5] For example, if a new species was given thespecific epithetalbum by Anton and attributed with uncertainty toAgenus, it could be denoted "Agenus?album Anton (?Anton)"; the "(?Anton)" indicates the author that assigned the question mark.[5] So if Anton describedAgenus album, and Bruno called the assignment into doubt, this could be denoted "Agenus?album (Anton) (?Bruno)", with the parentheses around Anton because the original assignment (toAgenus) was modified (toAgenus?) by Bruno.[5] This practice is not included in theInternational Code of Zoological Nomenclature, and is used only by paleontologists.[5]
In fungal taxonomy,incertae sedis is applied to taxa whose position in the hierarchy cannot be stated with confidence. For much of the discipline's history, classification rested onmorphology, and naming rules were periodically revised; changes to theICNafp adopted "one fungus, one name" and other measures to stabilise usage. DNA-based systematics, including multi-gene barcoding and model-based phylogenetics, has driven large rearrangements at genus, family, and order ranks. Even so, a sizeable residue of genera remains unplaced, including many that are morphologically well circumscribed and still listed asincertae sedis in major indexes such asSpecies Fungorum andMycoBank. Causes include limited taxon sampling, discordant signals from differentgenetic markers, missing links betweensexual andasexual morphs, and cases where a taxon simply does not match any recognised family or order.[18]
Progress is often slowed by practical constraints.Type material can be old, fragmentary, or inaccessible; loans from fungaria have tightened under biodiversity and quarantine rules, and the lack of living ex-type cultures hampers sequencing. Where fresh collections are possible,epitypes may be designated, although cautiously, since epitypification can be set aside only by formalconservation under the ICNafp. The scale of the backlog is substantial: the 2022 "Outline of Fungi and fungus-like taxa" reported about 3,185 genera asincertae sedis, including roughly 2,680 inAscomycota (around 1,477 of them not placed to any family or order) and about 420 inBasidiomycota, with smaller numbers in other groups. Continued recollection and molecular study are needed to place these taxa and to refine the fungal tree of life.[18]
^Yamaguchi, Masashi; et al. (28 September 2012). "Prokaryote or eukaryote? A unique microorganism from the deep sea".Microscopy.61 (6):423–431.doi:10.1093/jmicro/dfs062.PMID23024290.
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The dictionary definition ofincertae sedis at Wiktionary
Media related toincertae sedis at Wikimedia Commons
