GRANK, or Global Rank is a ranking of the rarity of a species, and is a useful tool in determining conservation needs.
They are based on the total number of known, extant populations worldwide, and to what degree they are threatened by destruction. Criteria also include securely protected populations, size of populations, and the ability of the species to persist.
- G1 — Extremely rare Usually 5 or fewer occurrences in the overall range or very few remaining individuals; or because of some factor(s) making it especially vulnerable to extinction.
- G2 — Very rare Usually between 5 and 20 occurrences in the overall range or with many individuals in fewer occurrences; or because of some factor(s) making it vulnerable to extinction.
- G3 — Rare to uncommon Usually between 20 and 100 occurrences; may have fewer occurrences, but with a large number of individuals in some populations; may be susceptible to large-scale disturbances.
- G4 — Common Usually more than 100 occurrences; usually not susceptible to immediate threats.
- G5 — Very common Demonstrably secure under present conditions.
- GH — Historic No records in the past 20 years.
- GU — Status uncertain Often because of low search effort or cryptic nature of the species; more data needed.
- GX — Globally extinct No recent records despite specific searches.
- ? Denotes inexact numeric rank (i.e. G4?).
- G A "G" (or "T") followed by a blank space means that the conservation data centre has not yet obtained the Global Rank from The Nature Conservancy.
- G? — Unranked Or, if following a ranking, rank tentatively assigned (e.g. G3?).
- Q Denotes that the taxonomic status of the species, subspecies, or variety is questionable.
- T Denotes that the rank applies to a subspecies or variety.