Rare Plant Management

Creekside Science is a leader in rare plant management. We have been leaders in recovery actions for
multiple taxa, including San Mateo thornmint (Acanthomintha duttonii), Metcalf Canyon jewelflower
(Streptanthus albidus ssp. albidus), Presidio clarkia (Clarkia franciscana), Crystal Springs fountain thistle
(Cirsium fontinale var. fontinale), Tiburon paintbrush (Castilleja affinis var. neglecta), and more. Our
services include surveys and mapping, demographic monitoring, threat assessment, management
planning, stewardship activities, propagation, and introductions.

San Mateo thornmint
San Mateo thornmint (Acanthomintha duttonii) is a federal- and state-endangered annual mint.
Historically it is known only from serpentine grassland vertisols in San Mateo County, and declined to
only one small location at Edgewood Preserve. This population had been documented at ~53,000
individuals in 1994, and dropped to only 249 individuals in 2008. The site was threatened with altered
hydrology and increasing nonnative cover. Creekside Science began an enhancement project onsite by
establishing propagation protocols with UC Berkeley Botanical Garden and experimenting with different
planting techniques. After establishing successful treatments (post germination scraping and seeding
was the initial winner), we began scaling up seeding at the original site. After two years of success, it
became apparent that the original site was unlikely to be self-sustaining. We sought additional seeding
sites, analyzing soil composition, soil moisture, and vegetative associates. We began seeding additional
sites in fall 2015, with the goal that after four years of seeding the new sites would perform at least half
as well as the original site. By 2022, we have hit a project high of ~51,000 plants at six locations. All of
the new sites are actually performing better than the original site, which has continued to decline. We
firmly believe the new introductions are critical to preventing extinction of this taxon. At this point we
have produced more than 730,000 seeds at the Creekside Science Conservation Nursery, and continue
stewardship that includes seeding, string cutting, and dodder pulling. Many of the planted cohorts are
exhibiting passive recruitment (increasing population numbers over multiple years without additional
seed input). We continue to work toward downlisting this plant with our multiple partners: USFWS,
CDFW, Friends of Edgewood, San Mateo County Parks, San Mateo County Park Foundation, SFPUC,
CNPS, and Yerba Bioadvocacy.

Hear more about the project when we speak at the October 2022 California Native Plant Society
conference in San Jose.

Metcalf Canyon jewelflower
The Metcalf Canyon jewelflower (Streptanthus albidus ssp. albidus) is a federally-endangered member
of the mustard family (Brassicaceae) known only from serpentine grasslands in Santa Clara County. It is
one of 18 species covered by the Santa Clara Valley Habitat Plan. Partnering with Dr. Justen Whittall of
Santa Clara University (SCU), we successfully introduced this taxon to an extirpated site in south San
Jose where they were last documented in 1980. More favorable grazing regimes, soil tests, vegetation
surveys, and other steps led this team to believe habitat was now favorable again for this taxon. Two
previously funded research projects identified (1) a positive response in growth and reproduction of the closely related subspecies most beautiful jewelflower (Streptanthus albidus ssp. peramoenus) to
simulated moderate grazing (Weiss et al. 2007), (2) that the site’s soil has similar physical and chemical
characteristics to existing S. albidus ssp. albidus populations (Whittall and Strauss 2011), and (3) the
site’s soil consistently fosters increased growth and flowering of S. albidus ssp. albidus compared to soil
from existing populations (Whittall and Straus 2011). These results coupled with the recently improved
grazing regime at the site strongly suggested it would support a healthy population of Metcalf Canyon
jewelflower given the appropriate reintroduction protocols.

We identified the four most likely sites for Metcalf Canyon jewelflower survival based on HOBO remote
climate monitors and field reconnaissance, compared with reference sites. Plants were started in pots at
the SCU greenhouse and matured outside to allow pollinator access. Plots were seeded at four locations
throughout the 330-acre site starting in 2014. By December 2015, 128,000 seeds were added to the site.
The plants are still extant as of 2022, and propagation has resumed at the Creekside Science
Conservation Nursery with the goal of increasing numbers and distribution of Metcalf Canyon
jewelflower on the site. Creekside Science and Dr. Whittall continue to collaborate on this project, now
seeking to understand the genetic basis of color differences between this taxon and the closely related
most beautiful jewelflower. These two taxa grow together in a blending zone on Coyote Ridge. The
Valley Habitat Plan has objectives related to number and size of occurrences of each protected, and
understanding the genetic basis of the multiple phenotypes will allow observers to confidently
categorize these blended colonies.

Tiburon paintbrush
Tiburon paintbrush (Castilleja affinis ssp. neglecta) is known from Marin, Napa, and Santa Clara
counties. The two Santa Clara County populations are disjunct from the others, and therefore the U.S.
Fish and Wildlife Service’s 1998 Recovery Plan for Serpentine Soil Species of the San Francisco Bay Area
deems their protection a high priority. After documenting reductions in one of the populations, we
tested whether different seeding treatments would facilitate recovery of this species. Different
propagation techniques, including alternate hosts, were also examined. We analyzed material from
extant sites to determine genetic distinctness of populations, informed enhancement and potential
future introduction decisions.

Seeding enhancement took place at CNDDB occurrence #9 (Paintbrush Canyon). The most successful
plots were in blocks that had high moisture, low December 21 insolation, and high Eriophyllum
cover, an important host. Irrigation and stratification were largely
useful, although we found ongoing irrigation on the site to be infeasible. After conducting GIS analysis,
we focused seeding areas with the lowest insolation, targeting those shady, moist sites with appropriate
hosts. Our introduced seeds have yielded reproductive plants and new seedlings in previously
unoccupied areas. Propagation continues at the Creekside Science Conservation Nursery.