BC Conservation Data Centre: Conservation Status Report
Eleocharis geniculata
bent spike-rush
| Scientific Name: | Eleocharis geniculata |
|---|---|
| English Name: | bent spike-rush |
| Provincial Status Summary | |
| Status: | S1S2 |
| Date Status Assigned: | April 30, 2019 |
| Date Last Reviewed: | April 30, 2019 |
| Reasons: |
Despite searches at many sites with appropriate habitat in the South Okanagan since 2002, only one population of Eleocharis geniculata is known in B.C., at Osoyoos Lake. The main natural limiting factor of Eleocharis geniculata is its restriction to a rather specific and geographically limited habitat. Although there is extensive shoreline habitat in the semi-arid interior portions of the province, few shorelines appear to have the flats or spits with isolated ponds that this species requires. Trampling and soil disturbance by livestock, human-related disturbances, invasive plants and artificial management of the water levels of Lake Osoyoos are threats, but these are somewhat mitigated by fencing and invasive species removal at the site. |
| Range | |
| Range Extent: | A = <100 square km |
| Range Extent Comments: | The extent of occurrence in B.C. is 1 square kilometre. The range in B.C. appears not to have changed over the short term, but Eleocharis geniculata may have been more widespread before the Zosel Dam was built in Oroville, Washington (COSEWIC 2008g). |
| Area of Occupancy (km2): | AD = 1-25 |
| Area of Occupancy Comments: | The area of occupancy is 4 square kilometres using a 2km x 2 km grid. |
| Occurrences & Population | |
| Number of Occurrences: | A = 1 - 5 |
| Comments: | Only one population of Eleocharis geniculata is known in B.C. at Osoyoos Lake. In 2007, searches were completed along the north, east and west shores of Osoyoos Lake, Vaseux Lake, Mahoney Lake,and Skaha Lake by T. McIntosh and C. Bjork. Between 2002 and 2003, Brian and Rose Klinkenberg surveyed specifically for this species at Deadman Lake, Gallagher Lake, Mahoney Lake, Okanagan Lake, Osoyoos lake, Prather Lake, Shannon Lake, Skaha Lake, Tugunuit Lake, Twin Lakes, Vaseux Lake, White Lake and others, plus associated wetlands. The shorelines that were investigated had receded considerably by the time searches were conducted, but this species may yet be found in some of these sites as additional drawdown could still have occurred and, because this species exhibits fluctuating numbers from year to year, populations may have been missed.with appropriate habitat in the South Okanagan since 2002 (COSEWIC 2008g). |
| Number of Occurrences with Good Viability / Ecological Integrity: | B = 1 - 3 |
| Comments: | Though it has not been observed every year, which is not unusual for an annual species, Eleocharis geniculata has persisted at this site since 1939. |
| Number of Occurrences Appropriately Protected & Managed: | B = 1 - 3 |
| Comments: | The B.C. population of Eleocharis geniculata is fenced protecting it from most livestock grazing and trampling. Also, the Osoyoos Indian Band has supported Habitat Stewardship Program for Species at Risk (HSP) conservation efforts since 2004. Most of this HSP work has been focused on invasive plant removal, especially in the sites where rare plant species have been found. Signage that denotes the rarity of the species in this area is located along the shore of the protected area (COSEWIC 2008g). |
| Population Size: | E = 2,500 - 10,000 individuals |
| Comments: | The number of mature individuals in 2007, based on visual estimates during walking transect surveys, is more than 10,000. These are all part of a single population (COSEWIC 2008g). There are extreme fluctuations in numbers of mature individuals. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Substantial, non-imminent threat |
| Comments: | In B.C., Eleocharis geniculata is restricted to a single site at Osoyoos Lake. Trampling and soil disturbance by cattle and horses, human-related disturbances, invasive plants, especially grasses are threats. However, a fence protects the population from most livestock grazing and trampling and the Osoyoos Indian Band has supported Habitat Stewardship Program (HSP) conservation efforts which have focused on invasive plant removal, especially in sites where rare plants have been found. Despite artificial management of the water levels of Lake Osoyoos, Eleocharis geniculata persists at this site, though it may take more time before the influence of managed water levels on the population becomes visible. The shoreline along many portions of Osoyoos Lake have slowly been eroded and this may eventually threaten the population of the bent spike-rush. Although there are currently no development plans for the area near the spit, this is a future possibility, which would increase the use of the spit site (COSEWIC 2008g). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | U = Unknown |
| Comments: | Fluctuation and trend data were not recorded before 2005, but the size of the population does not appear to have changed significantly from 2005 to 2007, though the survey for the species was much more thorough in 2007 than in the previous two years. Population size and density may have increased since the area was fenced, but this is not confirmed. In addition, data on population changes since lake levels have been artificially managed by the Zosel Dam in Oroville,WA are not available (COSEWIC 2008g). |
| Long-Term Trend: | DE = Decline of 30-70% |
| Comments: | In B.C., habitat for Eleocharis geniculata appears to have declined. Historically, this species probably occurred in similar spits and flooded ponds or meadows alongside Osoyoos Lake that have been lost over the past 100 years or so, mainly through urban or agricultural development. In the late 1990's, A. Ceska (personal communication 2007) observed the small-flowered lipocarpha on the Osoyoos Lake shoreline in the Town of Osoyoos. It was found in a habitat that resembled the flats on the Osoyoos Indian Band land where he had collected the bent spike-rush. This site was filled with sand about a year later and washrooms were built, completely destroying the site. Another site that may have housed the bent spike-rush is a very large, seasonally flooded flat at the north-west end of Osoyoos Lake. This area has been heavily altered through time by livestock and related activities yet the adjacent shoreline still houses a number of plant species often associated with the bent spike-rush (COSEWIC 2008g). |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Eleocharis geniculata is an annual plant that grows when conditions are favorable and as water recedes. Achenes are probably buried under a fine layer of soil and/or litter as water levels rise. Some achenes remain dormant as a seedbank, germinating when specific environmental signals occur. Dormancy can last for many years, possibly for decades. Dispersal is through movement of achenes as there is no means of asexual reproduction in this species. Achenes probably fall close to the plant but may be moved around the habitat by water flow or animals. In laboratory conditions, when first wetted, the achenes float, rapidly sink when the water is disturbed, then immediately float back to the surface. After a few hours they sink again and remain submerged. This may indicate that they will not travel long distances effectively. Because E. geniculata grows in open habitats, dispersal to other wetlands may occur via the feet of waterfowl, such as ducks or geese, or possible through foraging, although this is unknown for this species. The absence of this species in suitable habitats that are relatively close to occupied habitats, such as at Long Point, suggests that it normally only disperses over short distances (COSEWIC 2008g). |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: |
Eleocharis geniculata appears adapted to a relatively narrow ecological range/habitat. The single extant site occurs on wet, silty-sandy soil at the edges of open ephemeral pond wetland complexes on a broadly triangular spit that stretches into Osoyoos Lake. The ponds are flooded throughout much of the winter and dry into the summer, but usually flood again in late summer or early autumn as a result of lake level changes or late discharge groundwater from the mountains to the east of the lake. The autumn dry down that follows the flooding expose the soils necessary for the growth of Eleocharis geniculata. Also, the pond complexes in which the species is found are characterized by calmer water conditions as they are isolated from the wave action in Osoyoos Lake by sand dunes and vegetated flats. Eleocharis geniculata may also require the more complex silty-sandy soils that are found in the ponded areas rather than the sand that composes the lakeshore. In 2007, the pH of the surficial soil was approximately 8.0 at one site and 7.0 at a second site COSEWIC 2008g). Suitable habitat appears to be rare in B.C. Although there is extensive shoreline habitat in the semi-arid interior portions of the province, few shorelines appear to have the flats or spits with isolated ponds that the bent spike-rush requires. The only other known similar habitats are found at the northwest end of Osoyoos Lake. The apparent restriction to these habitats is supported by field research. Between 2005 and 2007, C. Björk and T. McIntosh have investigated numerous shoreline habitats in the Okanagan Valley, Thompson Plateau, Shuswap Lake, and Similkameen Valley, and have not observed this species outside of its known site. Earlier, R. and B. Klinkenberg conducted searches for this species along lake and pond shorelines from Osoyoos to Salmon Arm in the north Okanagan Valley, but failed to discover any new populations (COSEWIC 2008g). |
| Other Rank Considerations: | The probability of rescue occurring is extremely low because of the distances involved and the unlikelihood of long-distance dispersal of the species. |
| Information Gaps | |
| Research Needs: | |
| Inventory Needs: | Extensive searches of suitable habitat for this species in the South Okanagan, have been conducted by various botanists since 2002, Although the shorelines that were investigated had receded considerably by the time searches were conducted, this species may yet be found in some of these sites as additional drawdown could still have occurred and, because this species exhibits fluctuating numbers from year to year, populations may have been missed COSEWIC 2008g). |
| Stewardship | |
| Protection: | |
| Management: | |
| Version | |
| Author: | Donovan, M. |
| Date: | October 01, 2008 |
| References | |
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COSEWIC. 2008g. COSEWIC status report on Bent Spike-rush, Eleocharis geniculata. Prepared for Comm. on the Status of Endangered Wildl. in Canada. In press.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2008. Conservation Status Report: Eleocharis geniculata. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 8, 2026).