In the CNPS East Bay rarity ranking system, rank is determined by a combination of rarity and vulnerability, using the 13 criteria listed below. A species automatically receives an A1 rank if it has three or fewer populations in the East Bay, or if it is severely declining, i.e., if only one-quarter or less of its original known populations in the East Bay are still remaining.
Both state and locally rare plants are included, with state rare plants being designated by an asterisk preceding the rank. CEQA consideration is required for all A1 and A2 ranked plants, both state and locally rare, in Sections 15125c and 15380.
Only current, naturally occurring populations of native plants with confirmed identifications are considered when determining rank, except for the A1x rank which specifically addresses historical plants that once occurred in the East Bay but have not been seen in 25 years or more, and ranks with a “?” which specifically address plants with unconfirmed identifications.
A population is defined as one or more plants of a particular species within a quarter-mile radius, or more than a quarter-mile if there is no discontinuity of habitat. In the case of annuals, a population can cover more than a quarter-mile area if the plants appear to all be from the same seed bank. There is some flexibility in the quarter-mile factor and populations will often have outliers scattered beyond that distance that are still considered to be part of that population.
The Watch List (B and C ranks) addresses plants that are not currently rare or vulnerable in the East Bay but that could become so if certain conditions persist.
The 13 criteria used to determine the rarity and vulnerability of a species are:
(Subject to CEQA Consideration)
*A:
State and Federal ranked rare plants occurring in Alameda and Contra Costa counties, listed in CNDDB and/or the CNPS Inventory
(Includes species ranked *A1, *A2, *A1x, and *A1?)
(CEQA Consideration Required)
(Note: Several *A2 ranked species have multiple populations in the two counties, but are rare in the rest of the state, thus meeting the criteria of Small Geographical Range. In addition, many of these plants are endemic, reach their range limit in the East Bay, or occur in limited or threatened habitats)
A1:
1 to 3 current populations in Alameda and Contra Costa counties,
or assessed as vulnerable because they meet additional criteria
(CEQA Consideration Required)
A2:
4 to 6 current populations in Alameda and Contra Costa counties,
or assessed as vulnerable because they meet additional criteria
(CEQA Consideration Required)
A1x:
No current, naturally occurring populations in Alameda or Contra Costa county, but historical populations known from one or both counties. A plant or population is considered historical if it has not been found in 25 years or more.
(CEQA Consideration Required)
A1?:
Plants that may possibly occur in Alameda and Contra Costa counties, but there are questions about their identification or location
(Not Subject to CEQA Consideration)
(Not Subject to CEQA Consideration)
B:
7 to 12 current populations in Alameda and Contra Costa counties,
or assessed as potentially rare or vulnerable if certain conditions persist, such as weed invasions, development, poor grazing methods, water diversions, etc. (See CNPS Rare Plant Inventory | Glossary for more extensive lists of threats)
(NOTE: This rank includes some plants that are currently plentiful in the East Bay but vulnerable due to various current threats or conditions such as pathogens, aging populations with little regeneration, uncontrolled weed encroachment, animal grazing and damage (deer, cattle, pig), or occurring in limited, declining, or threatened habitats.
C:
13 to 20 current populations, but potential threats as above