Incertae sedis

Some living things are hard to group.

Scientists look for clues to find a group. Sometimes the clues are not clear.

A fossil might only be one tooth. This makes it hard to know the animal. This is why some things are called incertae sedis. It means we do not know their place. We must keep looking for more clues.

This helps us finish the puzzle.

Scientists use groups to organize all living things. They use a system called taxonomy to do this. This system is like a big family tree.

Sometimes, a living thing or a fossil does not fit. It is hard to tell which group it belongs to. When this happens, scientists use the term incertae sedis. This is Latin for "of uncertain position."

There are a few reasons why this happens. One reason is a poor description. If the first scientist did not give enough details, others may struggle. Another reason is missing clues. A fossil might only be a single tooth. This makes it hard to see the whole animal.

Scientists also use this term when they do not have enough data. They might not have the DNA or tissue needed. They prefer not to guess. They wait until they have more proof to find the right spot.

Scientists use a system called taxonomy to organize all living things. This system works like a giant family tree. Every animal, plant, or tiny cell has a specific spot on this tree. Sometimes, a scientist finds something that does not fit anywhere. They might find a new fossil or a strange tiny organism. When they cannot find the right group, they use a term called incertae sedis. This is a Latin phrase that means "of uncertain position."

It is a way for scientists to be honest about what they do not know. Using this term helps keep the rest of the tree organized and accurate.

There are several reasons why a living thing might be incertae sedis. One reason is a poor description from the start. If the first person to find it did not provide enough details, it is hard to place. Another reason is missing clues in fossils. A fossil might only be a single tooth or a small bone. Without more of the body, the whole animal remains a mystery. Scientists also use this term when they lack DNA. It is hard to get tissue from very rare organisms. They prefer not to guess the wrong spot.

History shows us that many things were once incertae sedis. New World vultures were once in this uncertain group. Scientists did not know which order they belonged to. Later, they were placed in a group called Cathartiformes.

A bird called Bocage's longbill was also in this state. It was listed as Passeroidea incertae sedis for a long time. In 2015, a study finally moved it to the family Motacillidae. This shows how science changes as we learn more. Many mysteries are eventually solved with better tools.

There are many different examples of these mystery groups in nature. The frosted phoenix moth is so rare that no family is known for it. There is also a single-celled organism called Parakaryon myojinensis. It has a position on the tree of life that is completely unknown.

In the world of fungi, the number of uncertain groups is very large. In 2022, a report showed about 3,185 genera were incertae sedis. Many of these belong to groups like Ascomycota or Basidiomycota. This shows that even with modern science, much remains to be found.

Think of the tree of life like a giant library. Every species is a book that needs a specific shelf. If a book has no title or cover, you cannot find its place. You might put it in a special box marked "unknown" for now.

This keeps the other books from getting lost or messy. As soon as you learn more about the book, you can find the right shelf. Incertae sedis is that special box for the mysteries of our world. It helps scientists keep working until the truth is clear.

In the study of biology, scientists use a system called taxonomy to organize every living thing. This system creates a complex hierarchy, much like a massive family tree. Every species, from a tiny bacterium to a giant whale, has a specific place within this tree. However, sometimes a discovery does not fit neatly into any existing branch. When a scientist cannot determine the correct taxonomic position for a group, they use the term *incertae sedis*. This is a Latin phrase that translates to "of uncertain position."

It serves as a formal way to acknowledge that a group's relationships are unknown or undefined.

There are several scientific reasons why a taxon might be labeled *incertae sedis*. One common cause is a poor or inadequate description. If the original researcher did not provide enough physical details, later scientists may struggle to categorize it. Another issue is the presence of extensive homoplasies. This occurs when different species evolve similar traits independently, which can mislead researchers during analysis. Additionally, apparent character state reversals or convergent evolution can make a species look more like one group when it actually belongs to another. These complexities create confusion that prevents a certain classification.

In the field of paleontology, the lack of physical evidence often leads to uncertainty. Many fossils are defined based only on partial information. For example, if a phylogenetic analysis—a study of evolutionary relationships—is built using soft tissue and vertebrae, a fossil consisting only of a single tooth cannot be placed accurately. Without more body parts to study, scientists cannot guess the correct position. They choose to label the taxon *incertae sedis* rather than risk an incorrect assignment. This is also true in modern molecular phylogenies. It is often very difficult to obtain tissue samples from rare organisms for DNA testing.

Without this genetic data, the organism's place on the tree of life remains a mystery.

Taxonomic uncertainty can also arise from scientific controversy. When researchers produce conflicting results, there may be no consensus on how a taxon relates to other organisms. Until the conflict is resolved through further study, the group remains *incertae sedis*. It is important to distinguish this from other types of uncertainty. For instance, *nomen dubium* refers to a name of unknown application, often because the original specimen is lost. Similarly, *cf.* is used in paleontology to suggest a specimen should be compared to a known species but is not a certain match. *Incertae sedis* specifically addresses the unknown evolutionary position, not just a confusing name.

History provides many examples of organisms that were once *incertae sedis* but were later classified. New World vultures, such as the California condor, were once placed in the class Aves *incertae sedis*. Scientists were unsure of their specific order until the order Cathartiformes was recognized.

Another example is Bocage's longbill, a passerine bird. It was classified as *Passeroidea incertae sedis* because its family was unclear. A 2015 phylogenetic study finally placed it within the family Motacillidae. These examples demonstrate how advancing technology and new research eventually solve taxonomic mysteries.

Today, many strange and unique organisms still occupy this uncertain status. The single-celled organism *Parakaryon myojinensis* has a position on the tree of life that is completely unknown. There is also "biological dark matter," which consists of genetic material from unidentified microorganisms that match no known species. In the world of insects, the frosted phoenix moth is so rare and obscure that it cannot be placed in any family within the Lepidoptera. Even ancient groups like the Ediacaran biota have an unclear position within Eukaryota. They might be related to fungi, algae, or perhaps even an entirely extinct kingdom.

The scale of this uncertainty is particularly large in the study of fungi. In 2022, the "Outline of Fungi and fungus-like taxa" reported approximately 3,185 genera as *incertae sedis*. This includes roughly 2,680 genera within the Ascomycota group and about 420 within the Basidiomycota group. Many of these fungi are well-described physically, yet they still do not match any recognized family or order. This backlog is caused by limited sampling and discordant signals from different genetic markers. As scientists continue to collect fresh samples and perform molecular studies, they will gradually move these mysteries from the "uncertain" box into their rightful places on the tree of life.