Incertae sedis
is a term used to define a taxonomic
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by (of uncertain family), (of uncertain suborder), (of uncertain order) and similar terms.


  • The fossil plant Paradinandra suecica
    Paradinandra suecica is a species of fossil plant from the Cretaceous of Sweden. It is of uncertain placement within the order Ericales, and was described in 2001.-Biostratigraphy:...

    could not be assigned to any family, but was placed incertae sedis within the order Ericales
    The Ericales are a large and diverse order of dicotyledons, including for example tea, persimmon, blueberry, Brazil nut, and azalea. The order includes trees and bushes, lianas and herbaceous plants. Together with ordinary autophytic plants, the Ericales include chlorophyll-deficient...

     when described in 2001.

  • The fossil Gluteus minimus
    Gluteus minimus (fossil)
    Gluteus minimus is a fossil from the Upper Devonian of Iowa. It was first collected in 1902, but only described in 1975. Each animal appears as a bi-lobed lens up to , and almost all specimens share the same slight asymmetry. The species is of uncertain affinities, having been thought of as either...

    was described in 1975, but could not be assigned to any known animal phylum
    In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

    . The genus is therefore incertae sedis within the kingdom Animal
    Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...


  • While it was unclear to which order the New World vulture
    New World vulture
    The New World Vulture or Condor family Cathartidae contains seven species in fivegenera, all but one of which are monotypic. It includes five vultures and two condors found in warm and temperate areas of the Americas....

    s (family Cathartidae) should be assigned, they were placed in Aves incertae sedis. It was later agreed to place them in a separate order, Cathartiformes.

  • Bocage's Longbill
    Bocage's Longbill
    The São Tomé Shorttail , also known as Bocage's Longbill, is a species of passerine bird in the superfamily Passeroidea. It is the only member of the genus Amaurocichla. Formerly placed in the family Sylviidae, appears to be close to the Motacillidae, though its relationships currently are unclear...

    , Amaurocichla bocagei, is a species of passerine bird
    A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...

     that belongs to the superfamily Passeroidea. Since it is unclear to which family it belongs, it is classified as Passeroidea incertae sedis.

Poor description

This excerpt from a 2007 scientific paper
Academic publishing
Academic publishing describes the subfield of publishing which distributes academic research and scholarship. Most academic work is published in journal article, book or thesis form. The part of academic written output that is not formally published but merely printed up or posted is often called...

 about crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s of the Kuril-Kamchatka Trench
Kuril-Kamchatka Trench
The Kuril–Kamchatka Trench or Kuril Trench is an oceanic trench in the northwest Pacific Ocean. It lies off the southeast coast of Kamchatka and parallels the Kuril Island chain to meet the Japan Trench east of Hokkaido...

 and the Japan Trench
Japan Trench
__notoc__The Japan Trench is an oceanic trench, a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean off northeast Japan. It extends from the Kuril Islands to the Bonin Islands and is at its deepest. It is an extension of the Kuril-Kamchatka Trench to the north and the...

 describes typical circumstances through which this category is applied in discussing:
...the removal of many genera
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 from new and existing families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 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 extensive homoplasies, apparent character state reversals and convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...


Not included in an analysis

If a formal phylogenetic analysis is conducted that does not include a certain taxon, the authors might choose to label the taxon incertae sedis instead of guessing its placement. This is particularly common when molecular phylogenies
Molecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...

 are generated since tissue for many rare organisms is hard to obtain. It is also a common scenario when fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 taxa are included since many fossils are defined based on partial information. For example, if the phylogeny was constructed using soft tissue and vertebrae as principal characters and the taxon in question is only known from a single tooth, it would be necessary to label it incertae sedis.


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 as incertae sedis until the conflict is resolved.

Lower taxonomic levels

As stated in the International Code of Botanical Nomenclature, only ranks higher than the genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 may be assigned incertae sedis; species must be assigned to genera and infraspecific taxa must be assigned to species. For uncertainties at lower levels, question marks may be used to denote a questionable assignment. For example, if a new species with the specific epithet album was discovered by Anton and attributed with uncertainty to Agenus, it would be denoted "Homo? novus Anton (?Anton)"; the "(?Anton)" indicates the author that assigned the question mark. So if Anton described Agenus album, and Bruno called the assignment into doubt, this would be denoted "Agenus? album (Anton) (?Bruno)", with the parentheses around Anton because the original assignment (to Agenus) was modified (to Agenus?) by Bruno.
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