Order (biology)

In the study of life, scientists use a hierarchical system to organize organisms. One essential level in this system is called an order. An order is a taxonomic rank used to classify living things. In the Linnaean taxonomy system, it sits between the rank of class and the rank of family. You can think of an order as a way to group several related families together. This helps scientists manage the massive variety of life on Earth.

How an order is defined depends on the work of a taxonomist. A taxonomist is a scientist who specializes in naming and classifying organisms. These experts decide which living things belong in a specific order. They also decide if a particular order should be recognized at all. There are no hard rules that a taxonomist must follow when describing an order. Because of this, there is often no exact agreement among experts. Some orders are accepted almost universally by the scientific community. Other orders are recognized only rarely by most researchers.

Naming these groups often follows specific linguistic patterns. Most order names are written starting with a capital letter. The suffixes, or word endings, change depending on the type of organism. For example, orders of plants, fungi, and algae use the suffix "-ales," such as Dictyotales. Birds and fishes use a Latin suffix that means "having the form of," such as Passeriformes. Many insect orders use a suffix that means "wing." However, naming is less consistent for other groups. Mammals, reptiles, amphibians, and invertebrates use various endings like Primates or Anura.

In zoology, some scientists use even more levels to organize the hierarchy. While the order is a standard rank, extra levels can be inserted. A superorder is sometimes placed directly above the order. A suborder is placed directly beneath it. Some researchers have proposed even more specific ranks. In 1986, Michael Novacek inserted the ranks of grandorder and mirorder. In 1997, McKenna and Bell used these same two levels between superorder and order. Michael Benton suggested a different position for them in 2005. He placed them between the superorder and the magnorder.

The history of this system began centuries ago. The German botanist Augustus Quirinus Rivinus first introduced the order as a distinct rank. He used it to classify plants in his treatises during the 1690s. Later, Carl Linnaeus applied the concept consistently to all of nature. He included minerals, plants, and animals in his 1735 work, Systema Naturae.

For plants, Linnaeus used orders to subdivide larger classes into smaller, more comprehensible groups. Some plant families today still use these old Linnaean names, which are called descriptive family names. Examples include the names Palmae or Labiatae.

In the field of botany, the use of ranks has evolved over time. The ranks of subclass and suborder are used as secondary ranks. Subclass is defined as being above the order, while suborder is below it. The superorder rank is also commonly used in plant science. This specific naming style was initiated by the publications of Armen Takhtajan starting in 1966. In the 19th century, the meaning of these words shifted. Works by scientists like Augustin Pyramus de Candolle used the term for groups we now call families. By the 1905 International Botanical Congress, the word order was reserved for a higher rank.

Zoology and virology also utilize the rank of order in unique ways. In zoology, Linnaean orders often refer to natural groups. Some of these names have remained in use for a very long time. For instance, the order Lepidoptera includes moths and butterflies. The order Diptera includes flies, mosquitoes, midges, and gnats. Viruses also have an ordinal level in their classification. From 1991 to 2017, order was the highest rank used for viruses. These virus orders use the suffix "-virales." In 2018, the International Committee on Taxonomy of Viruses added even higher ranks, such as the realm.