Incertae sedis

Incertae sedis (Latin for 'of uncertain placement')[2] or problematica is a term used for a taxonomic group where its broader relationships are unknown or undefined.[3] Alternatively, such groups are frequently referred to as "enigmatic taxa".[4] In the system of open nomenclature, uncertainty at specific taxonomic levels is indicated by incertae familiae (of uncertain family), incerti subordinis (of uncertain suborder), incerti ordinis (of uncertain order) and similar terms.[5]

New World vultures, such as the California condor, were placed incertae sedis within the class Aves until the recognition of the new order Cathartiformes.
Plumalina plumaria Hall, 1858 (6.3 cm tall), Upper Devonian of western New York State, US. Workers usually assign this organism to the hydrozoans (phylum Cnidaria, class Hydrozoa) or the gorgonarians (phylum Cnidaria, class Anthozoa, order Gorgonaria), but it is probably safest to refer to it as incertae sedis.[1]
The varanopids, a mysterious family of tetrapods, had controversial relationships with many other land tetrapods. Paleolontologists have mostly assigned them in the past as eupelycosaurian synapsids. Others have placed them as basal neodiapsids. A compromise is to place them as Amniota incertae sedis.


  • The fossil plant Paradinandra suecica could not be assigned to any family, but was placed incertae sedis within the order Ericales when described in 2001.[6]
  • The fossil Gluteus minimus, described in 1975, could not be assigned to any known animal phylum.[7] The genus is therefore incertae sedis within the kingdom Animalia.
  • While it was unclear to which order the New World vultures (family Cathartidae) should be assigned, they were placed in Aves incertae sedis.[8] It was later agreed to place them in a separate order, Cathartiformes.[9]
  • Bocage's longbill, Motacilla bocagii, previously known as Amaurocichla bocagii, is a species of passerine bird that belongs to the superfamily Passeroidea. Since it was unclear to which family it belongs, it was classified as Passeroidea incertae sedis, until a 2015 phylogenetic study placed it in Motacilla of Motacillidae.[10][11]
  • Parakaryon myojinensis, a single-celled organism that is apparently distinct from prokaryotes and eukaryotes.[12]

In formal nomenclature

When formally naming a taxon, uncertainty about its taxonomic classification can be problematic. The International 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 the genus may be assigned incertae sedis.[13]

Reason for use

Poor description

This excerpt from a 2007 scientific paper about crustaceans of the Kuril–Kamchatka Trench and the Japan Trench describes typical circumstances through which this category is applied in discussing:[14]

...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 extensive homoplasies, apparent character state reversals and convergent evolution.

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 are generated, since tissue for many rare organisms is hard to obtain. It is also a common scenario when fossil 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.[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 as incertae sedis until the conflict is resolved.[5]

Other ways of denoting uncertainty

Uncertain taxonomic assigations of other degrees may be denoted using the 'cf.' (before a taxon name) and '?' (after a taxon name) specifiers.[15]

In zoological nomenclature

In zoological nomenclature, "incertae sedis" is not a nomenclatural term at all per 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.[13]Article 36.1 In zoology, a name proposed conditionally may be available 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 the specific epithet album by Anton and attributed with uncertainty to Agenus, it could be denoted "Agenus? album Anton (?Anton)"; the "(?Anton)" indicates the author that assigned the question mark.[5] So if Anton described Agenus 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 (to Agenus) was modified (to Agenus?) by Bruno.[5] This practice is not included in the International Code of Zoological Nomenclature, and is used only by paleontologists.[5]

See also


  1. "Plumalina plumaria". JSJ Geology. Retrieved 20 January 2021.
  2. "Glossary". International Code of Zoological Nomenclature. International Commission on Zoological Nomenclature. Retrieved 12 June 2011.
  3. "Frequently Asked Questions". PLANTS database. United States Department of Agriculture. Retrieved 12 June 2011.
  4. Allaby, M. (1999). A Dictionary of Zoology. Oxford University Press. p. 704. Retrieved 5 January 2013.
  5. S. C. Matthews (1973). "Notes on open nomenclature and synonymy lists" (PDF). Palaeontology. 16 (4): 713–719. Archived from the original (PDF) on 27 July 2011.
  6. Jürg Schönenberger; Else Marie Friis (March 2001). "Fossil flowers of ericalean affinity from the Late Cretaceous of Southern Sweden". American Journal of Botany. 88 (3): 467–480. doi:10.2307/2657112. JSTOR 2657112. PMID 11250825.
  7. Richard Arnold Davis; Holmes A. Semken Jr. (24 January 1975). "Fossils of uncertain affinity from the Upper Devonian of Iowa". Science. 187 (4173): 251–254. Bibcode:1975Sci...187..251A. doi:10.1126/science.187.4173.251. JSTOR 1739069. PMID 17838783. S2CID 39189634.
  8. J. V. Remsen Jr.; C. D. Cadena; A. Jaramillo; M. Nores; J. F. Pacheco; M. B. Robbins; T. S. Schulenberg; F. G. Stiles; D. F. Stotz; K. J. Zimmer (2007). "A classification of the bird species of South America". South American Classification Committee. American Ornithologists' Union. Archived from the original on 10 October 2007. Retrieved 15 October 2007.
  9. J. V. Remsen Jr.; C. D. Cadena; A. Jaramillo; M. Nores; J. F. Pacheco; M. B. Robbins; T. S. Schulenberg; F. G. Stiles; D. F. Stotz; K. J. Zimmer (2011). "A classification of the bird species of South America". South American Classification Committee. American Ornithologists' Union. Archived from the original on 2 March 2009. Retrieved 12 June 2011.
  10. Per Alström, Knud A. Jønsson, Jon Fjeldså, Anders Ödeen, Per G. P. Ericson, and Martin Irestedt (2015). "Dramatic niche shifts and morphological change in two insular bird species". Royal Society Open Science. 2 (3): 140364. Bibcode:2015RSOS....240364A. doi:10.1098/rsos.140364. PMC 4448822. PMID 26064613.{{cite journal}}: CS1 maint: uses authors parameter (link)
  11. Rebecca B. Harris, Per Alström, Anders Ödeen, and Adam D. Leaché (2018). "Discordance between genomic divergence and phenotypic variation in a rapidly evolving avian genus (Motacilla)". Molecular Phylogenetics and Evolution. 120: 183–195. arXiv:1707.03864. doi:10.1016/j.ympev.2017.11.020. PMID 29246816. S2CID 3592799.{{cite journal}}: CS1 maint: uses authors parameter (link)
  12. 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. PMID 23024290.
  13. McNeill, J.; Barrie, F.R.; Buck, W.R.; Demoulin, V.; Greuter, W.; Hawksworth, D.L.; Herendeen, P.S.; Knapp, S.; Marhold, K.; Prado, J.; Prud'homme Van Reine, W.F.; Smith, G.F.; Wiersema, J.H.; Turland, N.J. (2012). International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011. Vol. Regnum Vegetabile 154. A.R.G. Gantner Verlag KG. ISBN 978-3-87429-425-6. Retrieved 28 July 2013.
  14. Graham J. Bird (2007). "Family incertae cedis" (PDF). Zootaxa. 1599: 121–149. doi:10.11646/zootaxa.1599.1.8.
  15. Bengtson, Peter (January 1988). "Open Nomenclature" (PDF). Palaeontology. 1 (31): 223–227.
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