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Species is the smallest grouping of organisms commonly recognized in taxonomy. If a species has multiple populations with significant morphological differences, it may be divided further into subspecies.

The species is the second part of an organism's scientific (Latin) name.

For some fungi, different stages of their life cycle used to be classified as separate species. In 2011, the International Botanical Congress decided to end this practice, with the change going into effect in 2013.[1]

Criteria for distinct species

A species is defined as a population that lacks gene flow with other populations.[2] There are three separate criteria commonly used by scientists to determine if species are distinct:[2]

  1. The Biological Species Concept: Species are separate if they are reproductively isolated, meaning they cannot or do not interbreed. They are also isolated if they produce offspring that are not viable or fertile.
  2. The Morphospecies Concept: Species are separate if they differ in "size, shape, or other morphological features".[2] This criterion is used if reproductive isolation cannot be determined, as for fossils, but it is still based on the assumption that reproductively isolated species will have different phenotypes. Also, there are no objective standards for which features should be used or to what degree they should differ.
  3. Phylogenetic Species: Each tip on a phylogenetic tree is a distinct species. However, not all phylogenies are determined in the same way. This criterion would also lead to the identification of many more species than the other two.

Although the term "species" is defined by reproductive isolation, this standard is not always used in practice.


  1. Hawksworth, D. L. (2011). "A new dawn for the naming of fungi: impacts of decisions made in Melbourne in July 2011 on the future publication and regulation of fungal names". MycoKeys. 1: 7–20.
  2. 2.0 2.1 2.2 Freeman, Scott (2002). Biological Science: Instructor's Edition. Upper Saddle River, NJ: Prentice Hall. p. 450-451. ISBN 0-13-009338-6.