CNPS.ORG Inventory of Rare and Endangered Plants - 7th edition interface
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Status: New Modifications to the CNPS Ranking System - Fri, Oct. 22, 2021 16:23 ET c

New Modifications to the CNPS Ranking System

The CNPS Ranking Working Group was formed to review the ranking system in the CNPS Inventory of Rare and Endangered Plants (Inventory) and discuss needed modifications. This group decided to discontinue the use of the R-E-D (Rarity-Endangerment-Distribution) Code and to instead convey this information in a clearer way through modifying the CNPS List and including other information in the Inventory. This decision and the associated modifications were approved by the CNPS Board of Directors at their August 2005 meeting. The following information is intended to provide an explanation of and rationale for this new change to the CNPS ranking system.


The R-E-D Code contains information on Rarity, Endangerment, and Distribution, ranked as a 1, 2, or 3 for each value (as below). This code was originally known as the R-E-V-D Code (through the 3rd edition 1980), and the V (Vigor) was removed in the 4th edition (1984).

R - Rarity

1 – Rare, but found in sufficient numbers and distributed widely enough that the potential for extinction is low at this time

2 – Distributed in a limited number of occurrences, occasionally more if each occurrence is small

3 – Distributed in one to several highly restricted occurrences, or present in such small numbers that it is seldom reported

E - Endangerment

1 – Not very endangered in California

2 – Fairly endangered in California

3 – Seriously endangered in California

D - Distribution

1 – More or less widespread outside California

2 – Rare outside California

3 – Endemic to California

Modifications Associated with R-E-D Code Discontinuation

The information contained in the R-E-D Code remains in the Inventory, but the following new modifications express it more clearly:

  • A new Threat Code extension has been added following the CNPS List (e.g. 1B.1, 2.2 etc.). This extension replaces the E (Endangerment) value from the R-E-D Code. The main difference is that the number coding is now reversed to reduce confusion and represent this information in parallel with the threat rankings that the California Natural Diversity Database (CNDDB) uses. Therefore the logic is reversed so that the lower the number, the higher the corresponding threat level.

New Threat Code extensions and their meanings:

.1 - Seriously endangered in California

.2 – Fairly endangered in California

.3 – Not very endangered in California

Note that all List 1A (presumed extinct in California) and some List 3 (need more information- a review list) plants lacking any threat information receive no threat code extension. Also, these Threat Code guidelines represent a starting point in the assessment of threat level. Other factors, such as habitat vulnerability and specificity, distribution, and condition of occurrences, are also considered in setting the Threat Code.

  • A “CA Endemic” entry is displayed in the Inventory entries for those taxa that only occur in California. This clearly highlights endemic taxa.

  • Information contained in the R (rarity) value of the RED Code is expressed by displaying the state rank (S-rank) of the CNDDB.

  • Out-of-state distribution information is retained by displaying the global rank (G-rank) of the CNDDB.

  • With the addition of G- and S-ranks, the following explanation of CNDDB ranking will be included in the Inventory as explanatory material.


Global Ranking

The global rank (G-rank) is a reflection of the overall condition of an element throughout its global range.

Species or Community Level

G1 = Less than 6 viable element occurrences (EOs) OR less than 1,000 individuals OR less than 2,000 acres.

G2 = 6-20 EOs OR 1,000-3,000 individuals OR 2,000-10,000 acres.

G3 = 21-80 EOs OR 3,000-10,000 individuals OR 10,000-50,000 acres.

G4 = Apparently secure; this rank is clearly lower than G3 but factors exist to cause some concern; i.e., there is some threat, or somewhat narrow habitat.

G5 = Population or stand demonstrably secure to ineradicable due to being commonly found in the world.

Subspecies Level

Subspecies receive a T-rank attached to the G-rank. With the subspecies, the G-rank reflects the condition of the entire species, whereas the T-rank reflects the global situation of just the subspecies or variety. For example: Chorizanthe robusta var. hartwegii. This plant is ranked G2TI. The G-rank refers to the whole species range i.e., Chorizanthe robusta. The T-rank refers only to the global condition of var. hartwegii.

State Ranking

The state rank (S-rank) is assigned much the same way as the global rank, except state ranks in California often also contain a threat designation attached to the S-rank.

S1 = Less than 6 EOs OR less than 1,000 individuals OR less than 2,000 acres

S1.1 = very threatened

S1.2 = threatened

S1.3 = no current threats known

S2 = 6-20 EOs OR 1,000-3,000 individuals OR 2,000-10,000 acres

S2.1 = very threatened

S2.2 = threatened

S2.3 = no current threats known

S3 = 21-80 EOs or 3,000-10,000 individuals OR 10,000-50,000 acres

S3.1 = very threatened

S3.2 = threatened

S3.3 = no current threats known

S4 = Apparently secure within California; this rank is clearly lower than S3 but factors exist to cause some concern; i.e. there is some threat, or somewhat narrow habitat. NO THREAT RANK.

S5 = Demonstrably secure to ineradicable in California. NO THREAT RANK.


1. In reality, more factors are reviewed than just numbers of element occurrences. Other considerations used when ranking a species or natural community include the pattern of distribution of the element on the landscape, fragmentation of the population/stands, condition of the individual populations, and historical extent as compared to the plant’s modern range. It is important to take a bird’s eye or aerial view when ranking sensitive elements rather than simply counting Eos.

2. Uncertainty about the rank of an element is expressed in two major ways:

By expressing the rank as a range of values: e.g., S2S3 means the rank is somewhere between S2 and S3. By adding a ? to the rank: e.g., S2? This represents more certainty than S2S3, but less than S2.

3. Other symbols:

GH All sites are historical; the element has not been seen for at least 20 years, but suitable habitat still exists (SH = All California sites are historical).

GX All sites are extirpated; this element is extinct in the wild (SX = All California sites are extirpated).

GXC Extinct in the wild; exists in cultivation.

G1Q The element is very rare, but there are taxonomic questions associated with it.

T Rank applies to a subspecies or variety

Rationale for the Modifications

Though the R-E-D Code has a long tradition within CNPS, it has caused confusion for users of the Inventory and results in duplication of CNPS and CNDDB staff effort. These modifications clearly highlight the threat component within the ranking system. This is beneficial because the CNPS List is now a more effective prioritization tool for conservation planning. Additional rationale for discontinuation of the R-E-D Code is given below:

  • The R value is mostly redundant vs. CNPS List (i.e. R=2 or 3, List 1B or 2; R = 1, List 4) and not as useful as a ranking tool as CNDDB G- and S-ranks. G- and S- ranks should be used as a finer cut for conservation prioritization (e.g. S1 = 1-5 occurrences, S2 = 6-20 occurrences). As CNDDB tracks individual occurrences, rarity values should come from them, not CNPS (who track by quad). It is difficult for CNPS to keep the R values “correct” and seems to be needless duplication of effort.

  • The E value seems the most important for conservation ranking, and the utility of this code is obfuscated by its placement in the poorly understood R-E-D Code. It is highlighted by being extracted from the R-E-D Code and incorporated as a Threat Code extension to the CNPS List. CNPS List is based on rarity, and thus the Threat Code extension clearly highlights the endangerment factor, and allows prioritization based on it. For example, a listing of 1B.1 indicates a taxon is very rare and very endangered, while a listing of 1B.3 indicates a taxon is very rare, but not endangered.

  • The D value primarily indicates whether the plant is a California endemic, or more or less widespread outside the state. The former can easily be determined from the distributional information, but distribution outside the state can be difficult and/or time-consuming to make objective and keep current. Adding the “CA Endemic” entry and displaying G-ranks conveys this information in a more efficient and accurate way.

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