Rare Plants 1

Friday, October 21 at 3:00-4:40 pm, Donner Room

*note alternate instances of this session – Saturday at 10am and Saturday at 1pm

Session Description: Rare plants make up one-third of California’s native flora. They encompass nearly every habitat type and elevation range, are beautiful, and are important contributors to pollinators, ecosystem functions, and the rich biodiversity of the state. While great progress has been made at broader levels—families and genera—the California flora is still far from being understood at the species-level and it’s expected that hundreds of taxa have gone unnoticed by taxonomists; most of these will have narrow ranges and thus be more vulnerable to human impacts. Powerful tools are now available to describe and understand plant diversity in California, including a host of reduced representation sequencing methods, to understand fine-scale diversity and evolution.

Session Chairs: Aaron E. Sims (California Native Plant Society, Sacramento, CA, USA) and Israel Borokini (University and Jepson Herbaria, University of California, Berkeley, Berkeley, CA, USA)

*Session generously sponsored by Nomad Ecology, LLC

---

26.1    Rare plants on the brink? Prioritizing the documentation of California rare and endemic plants that are wholly known from historical occurrences

Aaron E. Sims (California Native Plant Society, Sacramento, CA, USA), Kaitlyn Green (California Native Plant Society, Sacramento, CA, USA)

California is one of 36 biodiversity hotspots in the world, containing a rich and diverse flora with over 2,400 rare plant taxa, more than 1,350 of which are endemic to the state. The CNPS Rare Plant Program (RPP) has documented that 1.6% of California’s endemic flora described to science has gone extinct. Over the last year, the RPP has taken a more advanced step to track and assess the extantness of California’s most rare and endemic plant taxa by utilizing a Core Report developed within the new Rare Plant Inventory (RPI). One function of the Core Report summarizes element occurrence data from the California Department of Fish and Wildlife’s Natural Diversity Database that is used to identify and assess conservation priorities. Core Report data analyzed in spring 2022 indicates over 6% of California’s rarest endemic plant taxa are wholly known from historical occurrences, meaning their populations have not been documented or assessed in over 20 years, and an additional 3% are known from a total of 90-96% historical occurrences. This study has resulted in prioritizing the conservation of these rare taxa by 1) collecting and reviewing existing records that could potentially result in updating historical data and 2) conducting on-the-ground field surveys to re-document the historical occurrences. This talk will provide 1) a look into the Core Report developed to track the historical status of rare plant occurrences, 2) an overview of California rare plants known from 90-100% historical occurrences, 3) actions taken to obtain and update historical rare plant occurrence data, and 4) future steps to reach updated information on historical occurrences of these high-conservation priority rare plant taxa. Nearly 10% of California’s rare and endemic flora is known from 90-100% historical occurrences; the goal of this project is to significantly decrease this percentage and work to stave off the potential extinction of California’s rarest endemic plants.

---

26.2    Preventing extinction of San Mateo Thornmint

Christal Niederer (Creekside Science, Menlo Park, CA, USA), Stuart B. Weiss (Creekside Science, Menlo Park, CA, USA), Jimmy Quenelle (Creekside Science, Menlo Park, CA, USA), Marissa Kent (Creekside Science, Menlo Park, CA, USA), and Christopher Schwind (Creekside Science, Menlo Park, CA, USA)

In 2008, there was one extant occurrence of San Mateo thornmint (Acanthomintha duttonii). The state and federally endangered mint was struggling to persist, with only 249 individuals occupying 34 m², down from ~53,000 in 1994. This short-statured annual forb was newly competing against invading Italian ryegrass (Festuca perennis) and likely altered hydrology. Initial efforts focused on propagation and grass control at the original site. We identified a successful restoration treatment of post germination scraping and seeding in unoccupied areas. By 2010 we had 3,450 individuals occupying 102 m². But over the next few years, numbers at the original site began declining again. We searched for alternate seed introduction sites within the historic range, tested soil composition and moisture, and sought similar plant communities on similar serpentine grassland vertisols. In 2016, we began seeding additional sites. By May 2020, we documented ~43,000 plants occupying 540 m² at six occurrences, a huge success. The exceptional drought of 2021 led to a decline to ~30,000 individuals. Most cohorts declined, but some continued to passively increase even in extreme circumstances. This year saw an all-time project high of ~51,000 individuals at six sites. The Creekside Science Conservation Nursery has produced 47,000 to 180,000 seeds annually for more than five years. Seeds were carefully installed in individually marked plots at a rate of 500 seeds/m², with a minimum of 10,000 seeds/site/year. Now that we have documented success with our methods, we are scaling up by more haphazardly seeding larger macroplots, which are sampled rather than censused. Most of the new sites are outperforming the original site. We now believe focusing scarce resources on the original site would have been a poor decision. This project began with modest gains. Long timeframes can be needed to scale up successes and make solid progress toward recovery goals. We are excited to be increasing the resilience of this taxon and working toward downlisting it.

---

26.3    Experimental outplanting and adaptive management of the federally threatened Santa Cruz tarplant (Holocarpha macradenia) at Arana Gulch

Alison E. Stanton (Consulting Botanist, South Lake Tahoe, CA, USA), Travis Beck (Superintendent of Parks, City of Santa Cruz, Santa Cruz, CA, USA), Sylvie Childress (UC Santa Cruz Greenhouses, Santa Cruz, CA, USA), Todd Lemein (U.S. Fish and Wildlife Service, Ventura, CA, USA), Mark Ogonowski (U.S. Fish and Wildlife Service, Ventura, CA, USA), Kathy Lyons (Botanical Resources Group, Santa Cruz, CA, USA).

Arana Gulch, within the City of Santa Cruz, contains 30 acres of remnant coastal prairie that historically supported a large population of the annual Santa Cruz tarplant (SCT). The population has been perilously low since 2006, with fewer than 50 plants in most years. Seedbank data show a 100-fold decline in viable SCT seed density between 1999 and 2015. Consequently, the population may be at or near some unknown threshold of extirpation at the site. In 2015, the City, in conjunction with the Arana Gulch Adaptive Management Working Group (AMWG), re-introduced grazing to Arana Gulch with support from a local rancher willing to adjust grazing strategies to improve habitat conditions for SCT and to reduce the high non-native plant cover. Five years of grazing did not lead to any measurable increase in native species or SCT recruitment population. Therefore, the City initiated a project to begin experimental outplanting of container-grown SCT. The UC Santa Cruz Greenhouses propagated SCT using seed collected from Arana Gulch. 1,000 SCT were planted in the winter of 2021 and 1,200 were planted in winter of 2022. Student volunteers participated in the plantings. The experimental planting treatments represent a gradient of management intensity; no treatment, mowing, or sheetmulch (cardboard followed by a 2-3” layer of wood chips). Surviving SCT in the 2021 control/mow treatments were typical of naturally occurring plants (short stature with few flowerheads) and produced about 2,000 flowerheads. Unexpectedly, the SCT planted into sheetmulch grew extremely large and produced an estimated 50,000 flowerheads. The 2022 planting involved more consistent mowing, hand-weeding, and the addition of rice straw mulch. SCT blooms in August and 2022 survival and 2021 recruitment data will be presented. The plots are within a fenced pasture and not visible to the public, so a demonstration plot with educational signage was installed adjacent to the high-use trail.

---

26.4    Seed amplification and establishing propagation protocols for conservation of three endangered plants in Sonoma County, California

Ayla Mills (Laguna de Santa Rosa Foundation and Sonoma Ecology Center, Sonoma, CA, USA), Sarah Gordon (Laguna de Santa Rosa Foundation, Santa Rosa, CA, USA),

and Asa Voight (Laguna de Santa Rosa Foundation, Santa Rosa, CA, USA)

Conservation efforts for the Kenwood Marsh Checkerbloom (Sidalcea oregana ssp. valida), Sonoma Sunshine (Blennosperma bakeri), and Burke’s Goldfields (Lasthenia burkei) in Sonoma County are critical for preventing further population declines in these extremely rare plants. All three listed plant species occur in imperiled wetland habitats that have been highly altered through anthropogenic activities. While working as Nursery Manager for two non-profit organizations in Sonoma County (Sonoma Ecology Center and the Laguna de Santa Rosa Foundation), I successfully propagated wild collected seed of these three listed species and subsequently harvested millions of nursery grown seeds for future conservation use. The endangered plants were grown in containers under shadehouses and in raised beds. Plant propagation methods and timelines were carefully recorded to document the best strategies for growing each of these wetland species. Establishing successful propagation protocols and rare plant restoration methods is imperative for proper conservation and management of these unique plant populations. I hope to raise awareness by sharing my experiences and provide inspiration and guidance for other rare plant conservation efforts.

---

26.5    The state of rare plant seed collections in California: evaluating progress and gaps in the genetic resources stored in California Plant Rescue seed banks

Katie Heineman (Center for Plant Conservation, Escondido, CA, USA), Christa Horn (San Diego Zoo Wildlife Alliance, Escondido, CA, USA), Tina Stanley (Center for Plant Conservation, Escondido, CA, USA), and California Plant Rescue Network

California Plant Rescue (CaPR) is a collaborative of not-for-profit botanical institutions working to conserve the flora of the Golden State through long term conservation seed collections. We maintain a comprehensive database of seed collections held at our member institutions, which represents a comprehensive record of the conservation seed resources for rare plants in California. In 2019, CaPR received $3.6 million of state funding from the California Biodiversity Initiative to safeguard all of the rarest plant species in California in at least one seed collection. Here, I will share how this investment has reduced the geographic, phylogenetic, taxonomically, and functional bias in the species represented in conservation collection by incentivizing work in areas of the state that have not had previous seed collections funding. Geographically, we have significantly increased the proportional representation of rare species from northern California and higher elevations. We have doubled the number of rare species in families not typically held in garden collections on display, most notably Orobanchaceae and Brassicaceae. This initiative, while successful, is only the first step in securing the immense biodiversity of the California Floristic province: one ex-situ collection per species is not enough to conserve representative genetic diversity especially in a region facing wide-scale threats from wildfire and development. I will present the population level bias in our current collections, wherein populations on public lands and with low threat classifications have higher proportional representation in collection than those on private lands and higher threat classifications. Future efforts for our groups will focus on strategically increasing the number of populations for each species in collection while maximizing the geographic, and presumable genetic, diversity represented in collections.