The conservation status of a species is designated by a number (1-5) and preceded by a letter reflecting the appropriate geographic scale of the assessment. S Rank refers to "subnational" or the local/state status, while G Rank refers to the "global" status (looking at the species as a whole).
State Ranks (NatureServe)
S1 = generally 1-5 occurrences in the state. Critically imperiled in the state because of extreme rarity (often 5 or fewer occurrences) or because of some factor(s) such as very steep declines making it especially vulnerable to extirpation from the state.
S2 = generally 6-20 occurrences in the state. Imperiled in the state because of rarity due to very restricted range, very few populations (often 20 or fewer), steep declines, or other factors making it very vulnerable to extirpation from the state.
S3 = generally 21-100 occurrences in the state. Vulnerable in the state due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors making it vulnerable to extirpation
S4 = generally 101-1000 occurrences in the state. Apparently Secure—Uncommon but not rare; some cause for long-term concern due to declines or other factors.
SE = an exotic (non-native) species in the state.
SR = state rare, but not well enough understood for accurate ranking.
SH = Historic - occurred historically (as a native species) in the state, but is not currently known to be extant in the state. There is some possibility that it may be rediscovered. Its presence may not have been verified in the past 20-25 years.
SU = State Unrankable -the status of the taxon is not known. In many instances where a taxon is ranked “SU,” the taxon is known to be native to the state, but the number of current occurrences of the taxon (if any) is not known.
SX = Presumed Extirpated - Species or community is believed to be extirpated from the state. Not located despite intensive searches of historical sites and other appropriate habitat, and virtually no likelihood that it will be rediscovered.
SNR = taxon is not ranked or tracked within the state even if it exists there.
New England Rank
Division 1: Globally Rare Taxa occurring in New England. Taxa included in this Division have a global conservation status rank (GRank) of G1 through G3 or T1 through T3; they are critically imperiled, imperiled, or vulnerable (NatureServe 2012). Usually only a few occurrences of these taxa exist within our region, but for some species, such as Carex oronensis or Sabatia kennedyana, the majority of 5 occurrences of these highly ranked taxa occur in New England. GRanks for taxa in this Division appear under each relevant taxon in the list. See the appendix for further explanations of the Global Ranks.
Division 2: Regionally Rare Taxa. Within New England these taxa have 20 or fewer current (observed within the last 20-25 years) occurrences. This Division includes taxa that are rare or uncommon throughout their entire range as well as taxa that reach the edge of their distributional range in our region. It is important to conserve these edge-of-range occurrences as part of New England's natural heritage as well as to avoid shrinkage of these species' ranges. All taxa in Division 2 have GRanks of G4 or G5 (apparently secure to secure globally). A taxon with slightly more than 20 occurrences in New England might also be included in Division 2 if it is vulnerable to extirpation due to other important factors (population size and trends, area of occupancy, overall viability, geographic distribution, habitat rarity and integrity, and/or degree of protection). These taxa are denoted as 2(a).
Division 3: Locally Rare Taxa. These taxa may be declining in a significant part of their range in New England, or may have one or more occurrences of biological, ecological, or possible genetic significance. Division 3(a) are those taxa that have documented decline in a substantial portion of their range in New England, e.g. southern New England. Each state in the declining portion of the range will be listed following the Division designation in the List, e.g. MA,NH. Division 3(b) taxa are those that, based on their biology and geography within New England, have populations that are disjunct to such a degree that genetic isolation is suspected. For example, Lathyrus japonicus, is not rare in New England, but highly disjunct in Vermont. Occurrences in adjacent states in the US and provinces of Canada are considered when determining disjunction. Each state with one or more disjunct occurrence will be noted following the Division designation in the List, and the county of each disjunct occurrence will be listed in the notes under the taxon. For Division 3(b), only selected occurrences in a particular state are of conservation concern for the purposes of the Flora Conservanda list, not all occurrences of the taxon throughout New England. A taxon may be listed as Division 3 in one or more states (designated by an * following the state data), but is not considered to be regionally rare.
Division 4: Historic Taxa. This Division consists of taxa that once existed in New England, but have not been observed in natural occurrences on the landscape in the last 20 -25 years (depending upon each NHPs methodology). The purposes of this division are to generate interest in re-locating these taxa if they still exist and to illustrate the level at which species have been lost from the region. Division Indeterminate (IND.): Indeterminate Taxa. These taxa are under review for inclusion in one of the above divisions, but due to issues of taxonomy (at least for New England occurrences) or nomenclature, or because their status in the wild is not confidently understood, they cannot yet be designated to a particular division. The purpose of this division is to stimulate interest in taxonomic research and/or field surveys for these taxa to bolster our knowledge and understanding.
Global Ranks (NatureServe 2012)
G1= Critically imperiled - At very high risk of extinction due to extreme rarity (often 5 or fewer populations), very steep declines, or other factors. G2 = Imperiled - At high risk of extinction or elimination due to very restricted range, very few populations, steep declines, or other factors.
G3 = Vulnerable - At moderate risk of extinction or elimination due to a restricted range, relatively few populations, recent and widespread declines, or other factors
G4 = Apparently Secure - Uncommon but not rare; some cause for long-term concern due to declines or other factors.
G5 = Secure - Common; widespread and abundant
G#G# = Numeric range rank: - A numeric range rank (e.g., G2G3, G1G3) is used to indicate the range of uncertainty about the exact status of a taxon or ecosystem type. Ranges cannot skip more than two ranks (e.g., GU should be used rather than G1G4).
GNR = Unranked - Global Rank not yet assessed.
G#T# = for infraspecific taxa: the GRank applies to the full species and the TRank applies to the infraspecific taxon.
? = Inexact Numeric Rank. (For example, G3? or G5T3?) – denotes inexact numeric rank
Q = Questionable taxonomy that may reduce conservation priority - Distinctiveness of this entity as a taxon or ecosystem type at the current level is questionable; resolution of this uncertainty may result in change from a species to a subspecies or hybrid, or inclusion of this taxon or type in another taxon or type, with the resulting taxon having a lower-priority (numerically higher) conservation status rank. (For example, G3Q means that the taxonomy is questionable.)