Galena Rock Cress (Arabis Rigidissima V. Demote)
Galena Creek rockcress (Arabis rigidissima v. demote) is a slender perennial plant in the Brassicaceae (mustard) family. The species occurs on sandy to rocky soils or on outcrops derived from granitic or volcanic materials, mostly on moderate to steep terrain with northerly aspects. Galena Creek rockcress has a global rank of G3T3Q (vulnerable but has taxonomic questions), a state rank of S1 (critically imperilled), a California Native Plant Society Rare Plant Rank of 1B.2 (rare, threatened or endangered in California and elsewhere; fairly endangered in California), and is on the at-risk list of the Nevada Natural Heritage Program. The species is restricted to Washoe County in Nevada and Placer and Nevada counties in California, and just an estimated 10,000 individuals are known from private, state and USDA Forest Service land. The primary threats to the species are recreational activities that might trample or uproot plants (e.g., camping, hiking, equestrian use, trail construction, snowmobiles) and climate change. Projects such as fencing and signage near plants are aimed at reducing recreation impacts around known sites. Galena Creek rockcress is monitored by the USDA Forest Service.
2023 Evaluation
- Status
- Somewhat Worse Than Target
- Trend
- Insufficient Data to Determine Trend
- Confidence
- Low
Applicable Standard
VP22: Maintain a minimum of 7 Arabis rigidissima v. demote population sites.
Key Points
- Two additional occurrences in the Tahoe Region were identified in 2015, bringing the total to six. Misidentification of the species in the past has led to highly variable estimates of the number of occurrences in the Region, and a potentially unattainable threshold standard. No surveys have been done since 2015.
- There are no known disturbances that have impacted this species so the status is estimated to have remained the same.
- Galena creek rockcress is the lone sensitive plant species not in attainment. However, USDA Forest Service botanists questioned the identification of the desired number of plant populations as ever actually being accurately observed in the Region.
About the Threshold
- Galena Creek rockcress (Boechera rigidissima var. demote formerly known as Arabis rigidissima var demota) is a slender perennial plant in the Brassicaceae (mustard) family. The species occurs on sandy to rocky soils or on outcrops derived from granitic or volcanic materials, mostly on moderate to steep terrain with northerly aspects. It often occurs in drainage ways, near meadow edges, or in other moisture accumulating microsites, generally in openings in upper montane coniferous forest (Abies-Pinus) and aspen (Populus tremuloides) associations (Nevada Natural Heritage Program 2015a, CNPS Rare Plant Program 2016). It is difficult to identify in the field, and often forms hybrids with Elko rockcress (Boechera elkoensis = Arabis platysperma var. platysperma) (McKnight and Rowe 2015). Characteristics for positive identification include auriculate stem leaves, proximally pubescent stems, glabrous pedicels and fruits, narrow fruits (2.5 to 3.5 millimetres) that are erect but not appressed to rachis and basal leaves with branched hairs (2 to 5 rays) (Morefield 2001, McKnight and Rowe 2015). The taxon is classified under Boechera rigidissma in the Jepson Manual and Flora of North America (Al-Shehbaz and Windham 2003, Baldwin et al. 2012), but recent genetic work indicates var. demota is a distinct species of Boechera (McKnight and Rowe 2015). Galena Creek rockcress was first recommended for inclusion as a TRPA identified sensitive plant species in the 2001 Threshold Evaluation Report, based on the fact that it was identified as a focal species in the Lake Tahoe Watershed Assessment, and the U.S. Forest Service had listed it as a species of concern (Schlesinger and Holst 2000, TRPA 2001). However, TRPA did not evaluate the species in the 2006 Threshold Evaluation Report, citing concerns over the validity of the species and a lack of information (TRPA 2007). Galena Creek rockcress has a global rank of G3T3Q (vulnerable but has taxonomic questions), a state rank of S1 (critically imperilled), a California Native Plant Society Rare Plant Rank of 1B.2 (rare, threatened or endangered in California and elsewhere; fairly endangered in California), and is on the at-risk list of the Nevada Natural Heritage Program (Nevada Natural Heritage Program 2015, CNPS Rare Plant Program 2016). The species is restricted to Washoe County in Nevada and Placer and Nevada counties in California, with 41 element occurrences reported (Nevada Natural Heritage Program 2015) (seven element occurrences reported by CNPS Rare Plant Program), and an estimated 10,000 individuals are known from private, state and Forest Service land (McKnight and Rowe 2015). Taxonomic confusion and difficult identification have led to misidentification of many occurrences of Galena Creek rockcress (see above figure, part a), and fluctuations in the number of populations reported (McKnight and Rowe 2015). At present there are two populations with three subpopulations of Galena Creek rockcress verified in the Region (McKnight and Rowe 2015). Thus the species is likely more threatened in the Region than originally thought, and the current threshold standard of seven populations is likely not attainable.
- The primary threat to the species are recreational activities that might trample or uproot plants (e.g., camping, hiking, equestrian use, trail construction, snowmobiles) (McKnight and Rowe 2015). Other direct human threats include forest management such as road construction and maintenance, logging, fire suppression, and fuel reduction treatments (Morefield 2003, CNPS Rare Plant Program 2016). The small population sizes that are typical (e.g. all confirmed LTBMU populations are less than 150 individual plants) make this species susceptible to catastrophic loss from stochastic events. As with other high elevation species, changes in precipitation type, timing, and quantity associated with climate change may adversely affect the species by altering plant community composition and species interactions, and/or decoupling plant flowering periods and insect pollinator visitation.
Rationale Details
- Somewhat Worse Than Target. The USDA Forest Service has two confirmed occurrences with six sub-occurrences in the Tahoe Basin as of 2015. Earlier work had suggested that the species could be present at up to 18 other locations in the Region. However, the sites have been repeatedly revisited since 2012 and confirmed that the species was misidentified. The six sub-populations relative to the seven target populations mean the status is somewhat worse than target.
- Insufficient data to establish a trend. Based upon monitoring data from the six subpopulations collected between 2009-2015, the USDA Forest Service concluded there was insufficient data to determine the trend. One sub-population was decreasing, two were increasing, one was stable, and two had insufficient data to determine trends because they were recently discovered.
Confidence Details
- Low. There is low confidence in the number of Galena Creek rockcress populations and subpopulations since monitoring has not taken place since 2015.
- Low. Insufficient data to establish a trend.
- Low.
Additional Figures and Resources
No photos available.
LTBMU RARE BOTANICAL SPECIES – 2015 MONITORING REPORT
- Uploaded On
- 9/18/2024
- File Type
- Description
- LTBMU Summary of Monitoring and trends for rare botanical species in the Lake Tahoe region.