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Global Rank Values

The Global (G) Rank reflects the conservation status of a species from a global (i.e. rangewide) perspective, characterizing the relative rarity or imperilment of the species. Global conservation status ranks are based primarily on three factors: the number of occurrences; the total overall abundance of the element; and the overall size of the geographic range. Additional considerations include quality of the occurrences, ecological fragility, threats from human activity, and difficulty in providing appropriate management.

For discussion of factors used in determining species status ranks see: L. L. Master. 1991. Assessing threats and setting priorities for conservation. Conservation Biology 5:559-563.

Note: This is a list of the most commonly encountered ranks. For additional ranks, print or view our Adobe PDF list of rank and status codes.      Adobe Acrobat Reader

BASIC GLOBAL RANKS

GX = Presumed Extinct
Believed to be extinct throughout its range. Not located despite intensive searches and virtually no likelihood that it will be rediscovered.

GH = Possibly Extinct
Known only from historical occurrences. Still some hope of rediscovery.

G1 = Critically Imperiled
Critically imperiled globally because of extreme rarity or because of some factor(s) making it especially vulnerable to extinction. Typically 5 or fewer occurrences or very few remaining individuals (<1,000).

G2 = Imperiled
Imperiled globally because of extreme rarity or because of some factor(s) making it especially vulnerable to extinction. Typically 6 to 20 occurrences or few remaining individuals (1,000 to 3,000).

G3 = Vulnerable
Vulnerable globally either because very rare and local throughout its range, found only in a restricted range (even if abundant at some locations) , or because of other factors making it vulnerable to extinction. Typically 21 to 100 occurrences or between 3,000 and 10,000 individuals

G4 = Apparently Secure
Uncommon but not rare, and usually widespread. Possibly cause for long­term concern. Typically more than 100 occurrences globally or more than 10,000 individuals.

G5 = Secure
Common, typically widespread and abundant.

VARIANT GLOBAL RANKS

G#G# = Range Rank
A numeric range rank (e.g., G2G3) is used to indicate uncertainty about the exact status of a taxon.

GU = Unrankable
Currently unrankable due to lack of available information about status or trends.

G? = Unranked
Global rank not yet assessed.

HYB = Hybrid

RANK QUALIFIERS

? = Inexact numeric rank
Denotes inexact numeric rank.

Q = Questionable taxonomy
Taxonomic status is questionable; numeric rank may change with taxonomy.

C = Captive or cultivated only
Taxon at present is extant only in captivity or cultivation, or as a reintroduced population not yet established.

Z = Moving
Occurs as a diffuse, usually moving population; difficult or impossible to map static occurrences.

INFRASPECIFIC TAXON RANKS

T = Infraspecific Taxon (trinomial)
The status of infraspecific taxa (subspecies or varieties) are indicated by a "T-rank" following the species' global rank. Rules for assigning T ranks follow the same principles outlined above. For example, the global rank of a critically imperiled subspecies of an otherwise widespread and common species would be G5T1.