Database of Rare, Unusual and Significant Plants of Alameda and Contra Costa Counties

Database of Rare, Unusual and Significant Plants of Alameda and Contra Costa Counties

This database represents over 26 years of research and monitoring of locally rare and statewide rare plants by both the Rare and Unusual Plant Committees and their volunteers. It includes 1,014 plants with almost 18,000 observation records from a myriad of sources including CNPS volunteers, local botanists, herbaria records, etc.

Because the East Bay is very much of a melting pot for California vegetation, there are a great many plants that have very limited distribution in our two-county area. In 1989 the Rare Plant Committee started looking at the local flora in terms of local rarity, and by 1992 they had identified 658 taxa that had 5 or fewer locations in the East Bay. A database was set up to track these “Unusual and Significant” plants, and research and monitoring have continued ever since.

Access the Rare, Unusual and Significant Plant Database

Many of you are familiar with the report of the same name that was produced periodically from 1992 through 2010 for 8 editions. That report was a great success and became an invaluable tool for land managers, planners, agencies, conservationists, and others.

In 2010, however, our focus changed to putting the database on-line so that those professionals and amateurs, as well as the general public, could search for a greater variety of data, and data that might be more specific to their various projects and endeavors.

The Unusual Plants Committee has spent almost 5 years making changes and improvements to the database so that it will be user-friendly for multiple users. It can be searched for species or observation records, with 36 different search fields, such as location, rarity, habitat, blooming periods, etc. A “How To Use The Database” section is provided to assist users in learning how the database works and how they can find the data they seek.

Users will also be able to add their own observations to the database, and these will be reviewed and checked for accuracy before actually being added into the database.

We hope that the online database will be of great help and enjoyment to professionals and amateurs alike.

Dianne Lake, Chair, Unusual Plants Committee

Unusual And Significant Plants Of Alameda And Contra Costa Counties

Definition of Unusual Plants

The East Bay has a wealth of native plant species. Alameda and Contra Costa Counties act as a botanical melting pot where many native species reach their range limit in one of the two counties, and many others occur in habitats that are very limited, isolated, or threatened here. Still others are in severe decline due to habitat loss, weed and insect invasions, changes in land use, altered water courses, or other detrimental factors.

Many of the native plant species in our two counties have been found to be rare statewide and are thus given some level of protection. But there are many more species that occur in only a few places in Alameda and Contra Costa counties, even though they may be more common in other parts of California. Some of these species are even rarer in our area than the statewide rare plants that occur here.

The East Bay Chapter of CNPS has designated these species that are rare or threatened locally, but possibly more common elsewhere in the state, as “Unusual Plants.” These species are given some protection under CEQA in sections 15380 and 15125a (see the “Legal Implications and Protection for Unusual Plants” section below).

The term “Unusual” was chosen because when the Unusual plants program was first started back in the late 1980’s, it was a brand new concept, and the term “locally rare” at that time was usually interpreted to mean the statewide rare plants that occurred locally. Although the distinction between “locally rare” and “statewide rare” is clearer now, and many Chapters have since started their own “locally rare” programs, the name “Unusual” has persevered for our Chapter.

Determining and Tracking Our Unusual Plants

Many years of surveying, monitoring and research by many dedicated CNPS volunteers went into determining which plants of our local native flora qualify as Unusual plants.

When rare plant surveys were conducted every week, year round, back in the 1980’s and 90’s, the participants started noticing that some native plants were seen quite often, and others very rarely even though they were not designated as rare by state CNPS. Several years of combing through plant lists, herbarium vouchers, and other plant records, plus interviewing numerous local botanists and others, resulted in a list of “Unusual” plants for Alameda and Contra Costa counties.

A database was set up in the late 1980’s to track these plants, and surveying, monitoring, and other research activities have continued over the years so that we can constantly reassess and update the status of these plants in our two-county area.

Over the years, criteria were developed and location and ranking systems were devised to denote the degree of rarity and endangerment of these unusual plants in our two counties.

In 1991 a report was published, Unusual and Significant Plants of Alameda and Contra Costa Counties, with the results of this constant monitoring and research. Providing rank, locations and habitat for each species, the report quickly became an important tool for botanists, land managers, planners, researchers, consultants, conservationists, etc. in their work around the East Bay.

Although the report originally addressed only the locally rare plants, it now includes the statewide rare plants that occur here as well, and has been renamed Rare, Unusual and Significant Plants of Alameda and Contra Costa Counties.

The report has been updated periodically, and the last (8th ) edition was released March 2010.

Since the last edition of the report was released, efforts have turned more towards making the database behind the report available online so that more people can use it, search in multiple categories, and find data that meets their particular needs. As one might guess, this proved to be a much more daunting task than first envisioned. Although we have made great strides, we have found that there are still several things that need to be ironed out to assure accuracy and easy usability.

Work still continues in both the surveying and monitoring of our Unusual plants, and also in making the database publicly accessible. There have been many great volunteers over the years contributing to these efforts, but we can always use more help. See the “How You Can Help” section below to learn how you can contribute to the monitoring and preservation of the East Bay’s Unusual plants.

Importance of Unusual Plants

In many instances our Unusual plant species are even rarer and more threatened locally than several of the statewide rare plants that occur in the East Bay. The preservation of these locally rare populations is important for a multitude of reasons.

Isolated and range limit, or peripheral, populations have often been found to possess plants with greater genetic variation and better survival rates than those in populations occurring where the species is more common. In rapid and catastrophic extinctions of large populations, the plants on the periphery of a range or in isolated disjunct populations have often survived. Common species with large populations can often disappear rapidly in the face of a catastrophic event or a pathogen moving from plant to plant, but isolated populations can often escape this fate simply due to their distance from the main populations. Conditions at the range edges of a species, or in isolated populations, are often more hostile and plants there tend to develop stronger survival mechanisms. These isolated and peripheral populations can sometimes be the only hope for survival that a species has in the event of an environmental disaster, and thus it is essential to identify where these populations exist and to take the necessary steps to ensure their survival.

Several of our Unusual plants occur in habitats that are limited or threatened statewide as well as in the East Bay, such as vernal pools, alkali sinks, serpentine environments, and miscellaneous wetlands and riparian areas. Because these habitats are so limited, many of the species that occur in them are also rare or threatened. Many of the Unusual plants in the East Bay occur only in these limited or threatened habitats, although some can also be found in other types of habitats and are thus less vulnerable. By identifying the Rare and Unusual plants found in these local places, these declining or limited habitats can be identified and protected.

Clusters or suites of Rare and Unusual plants are sometimes found, and these “botanical hotspots” usually indicate special environmental conditions such as unique soils, water patterns, limited pollinators, or other factors that contribute to our local biological heritage and diversity and that need to be preserved. Studying the plants and conditions in these areas can also help us better understand what various rare plants need to survive and to define patterns and trends that may cause local rarity. Some of the “botanical hotspots” of the East Bay are Mt. Diablo State Park, Antioch Dunes National Wildlife Refuge, Flicker Ridge in Canyon, Black Diamond Mines Regional Preserve, Lime Ridge, Byron Hot Springs, Corral Hollow, Springtown Wetlands Preserve, Sunol and Ohlone Regional Wildernesses, Don Edwards National Wildlife Refuge (Warm Springs section), Redwood Regional Park, and the Mines Rd. area south of Livermore.

It is important to recognize that plants and their habitats are interdependent and when species are found to be in rapid decline in an area it is an indication that the natural resources and biodiversity of that area are in trouble. Studying and becoming aware of our local Unusual plants is not just about preserving individual species but is also a way to determine local botanical areas of native plant diversity, define places with threatened habitats or suites of endangered plants, define patterns and trends that cause local rarity, and identify areas in need of study or conservation that may have other special environmental factors.

Legal Implications and Protection for Unusual Plants

When several Unusual species occur on a property, even if there are no statewide rare plants there, it should be considered a significant impact under guidelines in the California Environmental Quality Act (CEQA) that refer to locally rare populations in sections 15380 and 15125a which address species of local concern and place special emphasis on environmental resources that are rare or unique to a region.

CNPS and other organizations and individuals have been instrumental in alerting local land planners and managers about the existence and importance of these Unusual plants during public review periods for EIRs and other land planning documents.

CNPS has also notified the cities and agencies of Alameda and Contra Costa Counties about the Rare and Unusual plants known to occur in each of their areas. A list of CEQA-protected species for their area has been provided to every city and agency along with a letter explaining the importance of these species, their legal protection, and the need to consider these species in any land use activities or changes in their area.

Location System for Unusual Plants: Regions and Specific Sites

A location system was developed using regions and specific sites rather than individual occurrences partially because of the difficulty of comparing many historical records for an area to current sites. Records from the late nineteenth and early twentieth centuries often merely describe a site as “Berkeley Hills” or “Oakland”, for example, and provide no further detail. Thus, when sites or multiple sites for a plant species are now found in these areas, it is usually impossible to determine if any of those sites correspond to the historical site, or if there were more, or possibly even less, populations of that particular species there in the past.

For this reason, specific location details are now always requested when populations are reported (although this specific location data is usually not made available to the general public because of past incidents of vandalism, over-collecting, etc).

The region system was developed by analyzing the two counties according to vegetation, geology, habitats, soil types, and other factors. The area was then divided into 40 botanical regions.

Each of these regions contains several specific sites (or sub-regions) within them, that cover a certain area such as Tilden Park, Antioch Dunes, Mt. Diablo, etc. Detailed locations are then described within these specific sites, but only the regions and specific sites are considered when determining the rank of a species.

Ranking System For Unusual Plants

The ranking system is first based on how many regions a plant occurs in, then on several other criteria including size of populations, limited or threatened habitat, stressed or declining populations, small geographical range, range limits, and other population threats. In addition, ranks are based on how many specific sites a plant occurs in within a region. In most cases, plants occurring in five or fewer regions (A-ranked plants) also have very few specific sites or individual locations within those regions. In a few cases, however, plants occurring in only a few regions have several specific sites within some of those regions, and/or several individual locations within those specific sites. In those cases, a species is sometimes given a lower rank.

Plants are ranked locally as A, B or C. Only current populations are considered when determining rank.

The A-ranked species are broken down into several sub-ranks:

*A1x, *A1 or *A2: Species in Alameda and Contra Costa counties listed as rare, threatened or endangered statewide by federal or state agencies or by the state level of CNPS.

A1: Species currently known from 2 or less regions in Alameda and Contra Costa Counties (but not rare statewide).

A2: Species currently known from 3 to 5 regions in the two counties (but not rare statewide), or, if more regions, meeting other important criteria such as small populations, stressed or declining populations, small geographical range, limited or threatened habitat, etc.

A1x: Species previously known from Alameda or Contra Costa Counties, but now believed to have been extirpated, and no longer occurring here.

A?: Species that have been reported in the two-county area but identification is questionable and the species may not actually occur here.

In addition to the A-ranked species, a two-tiered Watch List of B and C ranked plants tracks local native species that are not currently considered rare or endangered in the East Bay but that could become so if certain conditions persist such as over-development, water diversions, excessive grazing, weed or insect invasions, etc. B ranked species occur in 6 to 9 regions in the two counties or are otherwise subject to threat, and C ranked species currently occur in 10 to 15 regions here but have potential threats.

How You Can Help

The continued monitoring, tracking and preservation of our local native flora is dependent on the efforts of our many CNPS volunteers and others who provide data on the Rare and Unusual plants they find while working and hiking in the East Bay.

Below are links to two tables, one is of the rarest of the East Bay’s Unusual plants, and the other is of the Unusual plant populations most in need of updated data.

A-Ranked Unusual Plant Species Of Alameda and Contra Costa Counties: This is a list of our locally A-ranked Unusual plants and their rarity ranks (see above for explanation of rarity ranks). Note that there are 572 plants on this list! And that doesn’t include any of the 133 statewide rare plants that occur in our area! (See for the statewide rare plants that occur in our two counties).

Of these 572 A-ranked plants, 265 occur in only two or fewer regions here (see “Location System…” above for explanation of regions), and 229 occur in only three or four regions. 59 plants are only known historically from the two counties and probably no longer exist here (although miracles do happen), and 19 plants have some question about their identification or location.

Priority Unusual Plant Populations to Survey for: This is a list of the Unusual plant populations in our two counties most in need of updating. Although we have fairly current data for many of the plants on the A list, there are also many for which we do not. Most of these are populations that have not been reported for many years. That doesn’t mean that they are no longer there, or even that they haven’t been seen recently, it means that no one has reported them for a long time so we have no current records of them, and we need to know how these populations are doing.

The list includes location and habitat information, and also the last date the population was reported. In many cases the location descriptions are quite specific. A few even have GPS coordinates. But several of the locations are very general such as “Corral Hollow” or “Tilden Park”. One of the important pieces of updated information needed for these populations is more detailed location data. GPS coordinates are especially helpful.

Volunteers are needed to go out and hunt for and monitor these populations and report back to us about them. The Unusual Plant Program does not conduct formal surveys, but people are encouraged to go out on their own or to form groups among themselves to survey either specific areas for several plants, or to survey several areas for a specific plant.

Identifications need to be verified for accuracy, so it is always good to have someone in the group who is familiar with East Bay plants, or verifications can also usually be made at the Jepson Herbarium at UC Berkeley.

When reporting your findings, please be as detailed as possible about the locations. If you can supply GPS coordinates, that would be great!

Please review the two tables above and choose a plant(s) or location(s) you would like to survey. If there is a plant(s) on the A list that is not in the High Priority list, please contact me at and I can you send you locations for that plant. Or if there is a specific park or location that you would like to survey, let me know and I will send you a list of Unusual plants known from that location.

When reporting your results, an Unusual Plant Survey Form can be downloaded here, or you can just email me with your results. Please be sure to include the name of the plant, the date you saw it, the habitat it occurred in, and a detailed location description (and/or GPS coordinates). Also helpful are number of plants, area of the population, condition of the site, threats, and anything else you think is pertinent.

Your help is greatly appreciated and needed to keep our knowledge of our rare and threatened plants up to date. Together we can continue to monitor and protect the rarest of the rare of our East Bay native flora.