California Native Plant Society (CNPS) Rare Plant Ranking System
This page discuses the rarity index developed by the California Native Plant Society (CNPS).
The California Rare Plant Ranking System (RPRS) was created by the CNPS in 1968 to evaluate and assign the rarity and endangerment status of California flora. Threat ranks do not affect the amount of protection a plant receives, e.g. a CRPR 1B.3 plant has the same environmental protections as a CRPR 1B.1 plant.
Rare Plant Rank Determination
Scientists and volunteers work closely with the California Department of Fish and Wildlife's California Natural Diversity Database (CNDDB) to collect data. Threat Ranks typically do not get regularly updated after the initial ranking is designated, so the rank might not always represent the current level of threats associated with a given taxon. Whenever a major change such as adding, deleting, or changing a California Rare Plant Rank is considered, it must be reviewed by the CNPS, CNDDB, regional Plant Status Review Groups, members of the Rare Plant Status Review Forum, and other experts. The regional Plant Status Review Groups and Rare Plant Status Review Forum are organized by the CNPS. Volunteers can sign up to become a member of the Rare Plant Status Review Forum.  Volunteers can also apply to join any of the seven Plant Status Review Groups.  Each of the seven groups corresponds to a Jepson eFlora geographic subdivision.
Plants are assigned a California Rare Plant Rank (CRPR) of 1A to 4 in addition to a threat rank .1 to .3 (e.g. 1B.2).
|California Rare Plant Ranks |
|1A||Presumed Extirpated in CA, Rare or Extinct Elsewhere|
|1B||Rare, Threatened, or Endangered in CA and Elsewhere|
|2A||Presumed Extirpated in CA, Common Elsewhere|
|2B||Rare, Threatened, or Endangered in CA, More Common Elsewhere|
|3||More Information is Needed (Review List)|
|4||Limited Distribution (Watch List)|
|Threat Rank |
|.1||Seriously threatened: over 80% of occurrences threatened (high degree and immediacy of threat)|
|.2||Moderately threatened: 20-80% occurrences threatened (moderate degree and immediacy of threat)|
|.3||Not very threatened: less than 20% of occurrences threatened (low degree and immediacy of threat or no current threats known)|
- Santa Catalina mariposa lily photograph http://www.cnps.org/cnps/education/workshops/2016/0314_rare_plant.php
- CNPS Rare Plants website page https://www.cnps.org/rare-plants
- CNPS Rare Plant Status Review forum https://www.forum.cnps.org/
- CNPS Plant Status Review Group Application https://docs.google.com/forms/d/e/1FAIpQLSeW0Zm7zAavDHbWb1Kci3C61NSf-v4F2tv_4DjuHGaTC1R_xA/viewform
- CNPS Glossary of Terms and Field Descriptions http://www.rareplants.cnps.org/glossary.html#lists
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