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 International Union for Conservation of Nature does not normally make such designations, but may use the term in scientific discussion.[1]
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.[2] [3] Almost 75% of known species can be classified as "rare".[4]
Rare species are species with small populations. Many will move into the endangered or vulnerable category if the negative factors affecting them continue to operate. Well-known examples of rare species - because these are large terrestrial animals - include the Himalayan brown bear, Fennec fox, Wild Asiatic buffalo, or the Hornbill.
They are not endangered yet, but classified as "at risk",[5] [6] although the frontier between these categories is increasingly difficult to draw given the general paucity of data on rare species. This is especially the case in the world Ocean where many 'rare' species not seen for decades may well have gone extinct unnoticed, if they are not already on the verge of extinction like the Mexican Vaquita.[7]
A species may be endangered or vulnerable, but not considered rare if it has a large, dispersed population. IUCN uses the term "rare" as a designation for species found in isolated geographical locations. Rare species are generally considered threatened because a small population size is less likely to recover from ecological disasters.
Rare plants can be classified based on the size and distribution of their populations. Some species may be rare because they consist of only a few individuals, are confined to a limited geographic area, or both. Certain rare plants are found sparsely distributed across a wide area. Others might have a large number of individuals that are concentrated in a very small area, such as a single county or canyon. The rarest plants typically have both a small number of individuals and a very limited geographic range.
Assessments of the status of rare plants are conducted using the best available data and consider various factors, including:
A rare plant's legal status can be observed through the USDA's Plants Database.
| Name | Image | Last sighting | Estimated population | Endemic geographic location | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Common name | Scientific name | Lowest wildlife | Highest wildlife | Captive | Total lowest | Total highest | ||||
| Nilopegamys plumbeus | 1927 | ? | ? | 0 | ? | ? | ||||
| Melanomys zunigae | Critically Endangered, Possibly Extinct | 1949 | ? | ? | 0 | ? | ? | Lima Department, Peru | ||
| Cryptochloris wintoni | Critically Endangered, Possibly Extinct | ? | ? | 0 | ? | ? | ||||
| Dicerorhinus sumatrensis lasiotis | Critically Endangered, Possibly Extinct | After 1960 | ? | ? | 0 | ? | ? | Myanmar & Malay Peninsula, Malaysia / Thailand | ||
| Crocidura trichura | Critically Endangered, Possibly Extinct | 1986 | ? | ? | 0 | ? | ? | Christmas Island | ||
| Campephilus principalis bairdii | Critically Endangered | 16 March 1987 | ? | ? | 0 | ? | ? | Cuba | ||
| Capromys garridoi | Critically Endangered, Possibly Extinct | 1989 | ? | ? | 0 | ? | ? | Banco de los Jardins y Jardinillos, Canarreos Archipelago, Cuba | ||
| Peromyscus guardia | Critically Endangered, Possibly Extinct | 1991 | ? | ? | 0 | ? | ? | |||
| Uromys emmae | Critically Endangered, Possibly Extinct | 1994 | ? | ? | 0 | ? | ? | Owi Island, Indonesia | ||
| Crocidura wimmeri | Critically Endangered | 2008 | ? | ? | 0 | ? | ? | |||
| Lipotes vexillifer | Critically Endangered, Possibly Extinct | 2018 | ? | ? | 0 | ? | ? | |||
| Peromyscus mekisturus | Critically Endangered, Possibly Extinct | 1948 | 0 | 50 | 0 | 0 | 50 | |||
| Mesocapromys nana | Critically Endangered, Possibly Extinct | 26 October 1951 | 0 | 50 | 0 | 0 | 50 | Zapata Swamp, Cuba | ||
| Mystacina robusta | Critically Endangered, Possibly Extinct | 1967 | 0 | 50 | 0 | 0 | 50 | |||
| Bos sauveli | Critically Endangered, Possibly Extinct | 1988 | 0 | 50 | 0 | 0 | 50 | |||
| Pteralopex pulchra | Critically Endangered, Possibly Extinct | 17 May 1990 | 0 | 50 | 0 | 0 | 50 | |||
| Mesocapromys sanfelipensis | Critically Endangered, Possibly Extinct | 1978 | 0 | 99 | 0 | 0 | 99 | Cayo de Juan Garcia & Cayos de San Felipe, Cuba | ||
| Murina tenebrosa | Critically Endangered, Possibly Extinct | 1962 | 1 | 1 | 0 | 1 | 1 | Tsushima Island & Yakushima, Japan | ||
| Chelonoidis niger phantasticus | Critically Endangered, Possibly Extinct | N/A | 1 | 5 | 0 | 1 | 5 | Fernandina Island, Ecuador | ||
| Pteropus aruensis | Critically Endangered, Possibly Extinct | 1887 | 1 | 49 | 0 | 1 | 49 | Trangan, Indonesia | ||
| Nothophantes horridus | Critically Endangered | N/A | 9 | 9 | ? | 9 | 9 | Cattedown, Plymouth, United Kingdom of Great Britain and Northern Ireland | ||
| Ceratotherium simum cottoni | Critically Endangered (Possibly Extinct in the Wild) | N/A | ? | ? | 2 | 2 | 2 | |||
| Monodelphis unistriata | Critically Endangered, Possibly Extinct | 9 April 1899 | 2 | 10 | 0 | 2 | 10 | |||
| Rafetus swinhoei | Critically Endangered | N/A | 2 | 4 | 1 | 3 | 5 | |||
| Campephilus principalis principalis | Critically Endangered | 8 April 2022 | 3 (as of 8 April 2022)[9] | 3 (as of 8 April 2022) | 0 | 3 (as of 8 April 2022) | 3 (as of 8 April 2022) | |||
| Uromys porculus | Critically Endangered, Possibly Extinct | Between 1886 and 1888 | 3 | 3 | 0 | 3 | 3 | |||
| Uromys imperator | Critically Endangered, Possibly Extinct | c. 1960s | 3 | 3 | 0 | 3 | 3 | |||
| Pilosocereus robinii | Critically Endangered | N/A | 7 | 15 | 7 | 15 | Florida Keys, Mexico, Puerto Rico | |||
| Dryococelus australis | Critically Endangered | N/A | < 10 (as of 3 October 2021)[10] | < 10 (as of 3 October 2021) | < 10 (as of 3 October 2021) | < 10 (as of 3 October 2021) | Ball's Pyramid, Australia | |||
| Phocoena sinus | Critically Endangered | N/A | 10 (as of 5 May 2022)[11] | 10 (as of 5 May 2022) | 0 | 10 (as of 5 May 2022) | 10 (as of 5 May 2022) | |||
| Pseudoryx nghetinhensis | Critically Endangered | 2013 | 20 (as of 30 October 2021)[12] | < 100 (as of 20 August 2021)[13] | 0[14] | 20 (as of 30 October 2021) | < 100 (as of 20 August 2021) | |||
| Phalanger matanim | Critically Endangered, Possibly Extinct | 1997 | 40 | 40 | 0 | 40 | 40 | |||
| Ursus arctos gobiensis | Critically Endangered | N/A | 51 (as of 27 May 2022)[15] | 51 (as of 27 May 2022) | 0[16] | 51 (as of 27 May 2022) | 51 (as of 27 May 2022) | |||
| Cephalorhynchus hectori maui | Critically Endangered | N/A | 55 | 55 | 55 | 55 | ||||
| Trachypithecus poliocephalus | Critically Endangered | N/A | 65 | 67 | 65 (as of March 2018)[17] | 67 (as of March 2018) | ||||
| Rhinoceros sondaicus sondaicus | Critically Endangered | N/A | 76 (as of 20 September 2022)[18] | 76 (as of 20 September 2022) | 0 | 76 (as of 20 September 2022) | 76 (as of 20 September 2022) | |||
| Dicerorhinus sumatrensis sumatrensis | Critically Endangered | N/A | 75 (as of 18 December 2022)[19] | 85 (as of 18 December 2022) | 10 | 85 | 95 | |||
| Mitu mitu | Extinct in the wild | N/A | 0 | 130 | 130 | 130 | ||||
| Strigops habroptilus | Critically Endangered | N/A | 149 | 149 | 149 | 149 | ||||
| Pithecophaga jefferyi | Critically Endangered | N/A | 200 breeding pairs | 200 breeding pairs | 200 breeding pairs | 200 breeding pairs | ||||
| Gorilla gorilla diehli | Critically Endangered | N/A | 200 | 300 | 0 | 200 | 300 | |||
| Dicerorhinus sumatrensis harrissoni | Critically Endangered | N/A | < 250 (as of 24 February 2020)[20] | < 250 (as of 24 February 2020) | 0 | < 250 (as of 24 February 2020) | < 250 (as of 24 February 2020) | East Kalimantan, Indonesia & Sarawak, Malaysia | ||
| Viverra civettina | Critically Endangered, Possibly Extinct | 1993 | 249 | 249 | 0 | 249 | 249 | |||
| Cyprinodon diabolis | Critically Endangered | N/A | 263 (as of 29 September 2022)[21] | 300 (as of 11 May 2022)[22] | 475 (as of 4 May 2022) | 475 (as of 4 May 2022)[23] | Devils Hole, Death Valley National Park, United States of America | |||
| Eubalaena glacialis | Critically Endangered | N/A | 366 | 366 | 366 | 366 | ||||
| Nilssonia nigricans | Critically Endangered | N/A | 150 | 150 | 300 | 450 | 450 | Sultan Bayazid Bastami shrine at Chittagong | ||
| Gymnogyps californianus | Critically Endangered | N/A | 446 | 446 | 446 | 446 | ||||
| Zyzomys pedunculatus | Critically Endangered | N/A | 800 | 800 | 0 | 800 | 800 | |||
| Camelus ferus | Critically Endangered | N/A | 950 | 950 | 950 | 950 | ||||
| Gorilla beringei graueri | Critically Endangered | N/A | < 5,000 (as of 7 October 2022)[24] | < 5,000 (as of 7 October 2022) | 1 | < 5,000 or 5,000 | < 5,000 or 5,000 | |||
Notes: