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.
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
? = 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.