Slender-petaled thelypodium is a California endangered plant species, which means that killing or possessing plants is prohibited by the California Endangered Species Act (CESA). Slender-petaled thelypodium is also listed as endangered under the federal Endangered Species Act. Slender-petaled thelypodium is a slender plant in the mustard family with thick purple-tinted leaves and lavender to white flowers that bloom from May to September. It is thought to be a biennial species, meaning it has a two-year life cycle, but this has not been verified by research. Research has shown that drought years can cause slender-petaled thelypodium to act as an annual.
Slender-petaled thelypodium is found in the Big Bear Valley of the San Bernardino Mountains in vernally moist alkaline meadows, meaning the water dries out and evaporates from the meadows in the summer, leaving dry, cracked soil often encrusted with salt and other minerals. Slender-petaled thelypodium is one of few plants that can tolerate these conditions. According to the 2011 U.S. Fish and Wildlife Service Five Year Review for Slender-Petaled Thelypodium, this habitat type has decreased by 91 percent in the Big Bear Valley since the early 1900s, following the construction of Big Bear Dam and the development it supported. At the time of this webpage posting, the California Natural Diversity Database (CNDDB) lists nine occurrences that are presumed to still exist, and two occurrences that have become extinct. However, the U.S. Fish and Wildlife Service Five Year Review considers only six of these occurrences to still exist. All of the occurrences are within four main areas: the south shore of Big Bear Lake, Baldwin Lake, Erwin Lake, and Holcomb Valley. It is unknown what the original distribution of slender-petaled thelypodium was beyond the eleven historical occurrences listed in the CNDDB, but it is thought to have been more abundant and have much more available habitat prior to the construction of Big Bear Dam.
The three main threats to slender-petaled thelypodium are development, off-highway vehicle usage, and altered hydrology. Development likely caused many of the historic occurrences to go extinct, and has caused known occurrences to go extinct after slender-petaled thelypodium was listed as endangered. Development remains a threat because most occurrences are on privately-owned land and are not protected. Off-highway vehicle use also threatens slender-petaled thelypodium, and has contributed to the extinction of occurrences in the past. Slender-petaled thelypodium depends on a very specific hydrological habitat, and development within and surrounding this habitat causes changes to soil hydrology that can impact the plant. Additional threats include invasive plant encroachment, grazing activities, recreation, fire management activities, extinction from a random event, and climate change.
In order to ensure the continued existence of slender-petaled thelypodium, agencies should work with landowners to protect occurrences and identify conservation opportunities on private land. Surveys should be conducted to verify the existence and health of current occurrences. Research into the life history and specific habitat requirements, as well as seed banking, should also be conducted to facilitate possible future reintroduction experiments.
CDFW may issue permits for slender-petaled thelypodium pursuant to CESA, and you can learn more about the California laws protecting slender-petaled thelypodium and other California native plants. Populations of slender-petaled thelypodium occur in CDFW’s Inland Deserts Region. More information is also available from the U.S. Fish and Wildlife Species Profile for Slender-Petaled Thelypodium.