The following Participating Institutions are custodians for this species in the CPC National Collection:
Rae Selling Berry Seed Bank & Plant Conservation Programs
Rancho Santa Ana Botanic Garden
The conservation of Rorippa subumbellata is fully sponsored.
Edward Guerrant, Ph.D. contributed to this Plant Profile.
Lake Tahoe is a popular vacation destination for many Americans. Perhaps, too popular. This hot-spot for boaters and sunbathers is the only naturally occurring site of the Lake Tahoe yellowcress. Rorippa subumbellata inhabits a seven-foot "tidal" zone between the low and high water lines of Lake Tahoe. This low-growing perennial has proven to be adaptable from year to year depending on the amount of rainfall. During years with low rainfall, the cress can grow lower on the exposed beach from seed or rootstock. In years of higher rainfall, the cress is limited by the availability of exposed beach. This delicate lakefront habitat is threatened by constant abuse from boat wake, dock construction, and uncontrolled recreation. Due to continuous abuse of the unique Lake Tahoe yellowcress habitat, only an estimated 14 of the 48 historically known populations survive.
Efforts are being made to limit construction and the degradation of the yellowcress' habitat. This mustard family member has been listed as "Endangered" by the state of California since 1982 and "Critically Endangered" by the state of Nevada since 1980. On December 11th 2000, the League to Save Lake Tahoe and the Center for Biological Diversity submitted a formal petition to the U.S. Fish & Wildlife Service to list the Tahoe yellow cress as an Endangered species. Without federal protection and the efforts of local conservationists and Tahoe area residents, the plant will continue to slide toward extinction.
Distribution & Occurrence
Coarse sand and sandy soil of beaches, dunes, stream inlets, and backshore depressions along the shore of Lake Tahoe, high in the Sierra Nevada Mountains, almost exclusively between the elevations of 6223 ft and 6230 ft.
CA: n SNH- northern High Sierra Nevada (Lake Tahoe Basin) (El Dorado and Placer Co.)
Beaches surrounding Lake Tahoe
|There are approximately 42 different sites around the lake where Rorippa subumbellata has been found at some point since surveys began in 1979. Many may have been extirpated, and populations seem to come and go depending on the conditions (California State Lands Commission 1998). In 1999, 14 sites were observed: 5 on private property, 9 on federal land. The number and size of populations fluctuates with changing lake levels (USFWS 2000).|
Conservation, Ecology & Research
Seed and plant material may be dispersed by wind and wave action, leading to colonization of new sites (NFGEL 2000).
Associated species include: Carex douglasii, Phacelia hastata var hastata, Juncus balticus, Salix spp., Lepidium virginicum var. pubescens, various grasses. (Reynolds 1988).
Little is known about the reproductive biology of this species. The method of pollination is not known (NFGEL 2000).
Soil/sand disturbance (CA Dept. of Parks and Recreation 1991).
Rising lake levels (Reynolds 1988).
Grazing (Ferreira 1986).
Germination trials at The Berry Botanic Garden yielded no germination of apparently good seed. Seeds were either cold stratified or not, and then subjected to either constant 68F (20C) or alternating 50F/68F (10C/20C) temperatures. Further research is needed to determine optimum germination requirements (BBG File). If no success is achieved, seed viability tests should be conducted.
Ongoing biological studies by the Tahoe-Baikal Institute. Student interns have studied human disturbances, monitored populations, and observed the pollinators of Rorippa subumbellata.
Three sites on U.S. Forest Service land were planted with 500 seedlings each in 1988. Populations were surveyed in 1990 and again in 1993. There was an overall survival rate of 12 to 43% (California State Lands Commission 1998).
In 1999, the Tahoe-Baikal Institute directed a study to monitor all populations of the Tahoe Yellowcress. They designed a protocol that could be followed to monitor the plant from year to year. They also recommended future management strategies that may contribute to the conservation of the Tahoe yellowcress in the basin.
A draft Conservation Strategy is being written and should be finalized and distributed in the spring of 2002 (Gross, pers. comm.)
Seeds from three sites are stored at The Berry Botanic Garden.
Investigate possible mycorrhizal associations and other vegetation relationships.
Maintain and protect populations, especially the three largest, which contain different alleles than the smaller populations (NFGEL 2000).
Determine how long dormant plants can survive inundation by lake water.
Determine the dominant method of site colonization. Is it by seed, re-sprouting roots, or deposition of plant material (i.e. fragments) Determine success of reproduction.
Study the longevity and viability of seeds.
Study pollination and reproductive biology. Determine patterns of gene flow.
If worse comes to worst, manipulate lake levels in order to create more suitable habitat and promote establishment.
Study the biological and ecological reasons for this species' rarity, including: population structure and dynamics, life history, and environmental requirements (California State Lands Commission 1998).
Determine if seeds can effectively be stored for long periods of time.
Collect and store seeds from populations around the lake, especially from populations that contain unique genes.
Determine effective propagation and re-introduction methods.
Mozingo, H.N.; Williams, M. 1980. The threatened and endangered plants of Nevada. Portland, OR: U.S. Fish & Wildlife Service and Bureau of Land Management. 268p.