A rare species is a group of organisms that are very uncommon, scarce, or infrequently encountered. This designation may be applied to either a plant or animal taxon, and is distinct from the term endangered or threatened. Designation of a rare species may be made by an official body, such as a national government, state, or province. The term more commonly appears without reference to specific criteria. The IUCN does not normally make such designations, but may use the term in scientific discussion.
Rarity rests on a specific species being represented by a small number of organisms worldwide, usually fewer than 10,000. However, a species having a very narrow endemic range or fragmented habitat also influences the concept. Almost 75% of known species can be classified as "rare".
The International Union for Conservation of Nature uses the term "rare" as a designation for species found in isolated geographical locations. They are not endangered, but classified as "at risk".
A species may be endangered or vulnerable, but not considered rare if it has a large, dispersed population. Rare species are generally considered threatened because a small population size is more likely to not recover from ecological disasters.
Rare species are species with small populations. Many move into the endangered or vulnerable category if the negative factors affecting them continue to operate. Examples of rare species include the Himalayan brown bear, Fennec fox, Wild Asiatic buffalo and Hornbill.
A rare plant's legal status can be observed through the USDA's Plants Database.