BC Conservation Data Centre: Conservation Status Report
Epilobium densiflorum
dense spike-primrose
| Scientific Name: | Epilobium densiflorum |
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| Scientific Name Synonyms: |
Boisduvalia densiflora
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| English Name: | dense spike-primrose |
| Provincial Status Summary | |
| Status: | S2 |
| Date Status Assigned: | March 31, 2018 |
| Date Last Reviewed: | April 30, 2019 |
| Reasons: | Five of an original 19-31 populations of Epilobium densiflorum are known to have survived in B.C., with three occurrences considered to have good viability. One occurrence is located within a protected area, but it is threatened by encroachment of woody species, and no management plan exists to ensure its viability. A large population occurs within an area with restricted access to the public. The species' range in B.C. has diminished from 2000 square kilometres in 1850 to about 900 square kilometres today. Some of the remaining populations are reduced to 1 square metre or a single plant. More than 70% of known occurrences have declined over the last 150 years. Threats are severe, pervasive, and imminent. Dispersal is limited, and genetic exchange appears to be nonexistent. Habitat specificity is high. |
| Range | |
| Range Extent: | C = 250-1,000 square km |
| Range Extent Comments: | The range extent of Epilobium densiflorum currently is known to cover about 900 square kilometres in the Victoria area. Historically, it covered about 2000 square kilometres, ranging from Victoria to Qualicum Beach and North Pender Island, but the populations at Qualicum Beach and North Pender Island could not be relocated in 2001 and are presumably extirpated (Fairbarns et al. 2004). |
| Area of Occupancy (km2): | AC = 1-5 |
| Area of Occupancy Comments: | In B.C., Epilobium densiflorum occupies less than 1000 square kilometres of suitable habitat (Fairbarns et al. 2004). The occupied area of the four extant populations is 0.1 square kilometre. |
| Occurrences & Population | |
| Number of Occurrences: | A = 1 - 5 |
| Comments: | Five of an original 19-31 reports of Epilobium densiflorum in B.C. are known to have survived (the exact number of reports is uncertain because of variable place names or vague localities). The earliest sighting was in 1887 (Faribarns et al. 2004). |
| Number of Occurrences with Good Viability / Ecological Integrity: | B = 1 - 3 |
| Comments: | Only three occurrences of Epilobium densiflorum are considered to have good viability in B.C. One of the two less viable populations was reduced to a single reproductive plant in 2003 (Fairbarns et al. 2004). However, in 2009, a large and previously unknown l population with from 20,000 to 90,000 plants was discovered i (J. Miskelly, pers. comm.). |
| Number of Occurrences Appropriately Protected & Managed: | B = 1 - 3 |
| Comments: | There is only one occurrence of Epilobium densiflorum in a protected area, but it is threatened by encroachment of woody species (Fairbarns et al 2004), and no management plan exists to ensure its viability. |
| Population Size: | F = 10,000 - 100,000 individuals |
| Comments: | There is a total of from 20,000 to 90,000 plants in the B.C. populations (J. Miskelly, pers. comm.). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Substantial, imminent threat |
| Comments: | The most serious threat to Epilobium densiflorum is habitat loss associated with ongoing urban and residential development throughout its range on Vancouver Island. The Victoria metropolitan area, in which two of the four known remaining populations occur, experienced a human population increase of 57% between 1966 to 1996, a trend that is likely to continue. Similar growth is occurring in the Nanaimo area where the largest known occurrence of E. densiflorum is threatened by the proposed development of a trailer park (Fairbarns et al. 2004). Other threats are grazing, fire suppression, and the spread of invasive exotic species (Fairbarns et al. 2004). Grazing may have first benefited E. densiflorum by keeping habitats open in the absence of fire, but it also facilitated the establishment and spread of exotic species. Fire suppression has enabled trees and shrubs to encroach on meadow habitat, particularly Alnus rubra, Pseudotsuga menziesii, Populus tremuloides, Symphoricarpos albus, and Rosa nutkana. Invasive exotic shrubs impacting E. densiflorum include Crataegus monogyna, Cytisus scoparius, Rubus armeniacus, and Rubus laciniatus. Invasive grasses include Agrostis gigantea, Agrostis stolonifera, Aira caryophyllea, Aira praecox, Anthoxanthum odoratum, Bromus hordeaceus, Cynosurus echinatus, Holcus lanatus, Phalaris arundinacea, and Vulpia bromoides. Invasive herbs include Barbarea vulgaris, Hypericum perforatum, Hypochaeris radicata, Leucanthemum vulgare, Lythrum salicaria, Plantago lanceolata, Ranunculus repens, Rumex acetosella, and Vicia sativa. These invasive species threaten Epilobium densiflorum by making its habitat too shady, outcompeting it for moisture and nutrients, and most importantly, pre-empting sites for germination (Fairbarns et al. 2004). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | F = Decline of 10-30% |
| Comments: | There has probably been a moderate decline of known occurrences of Epilobium densiflorum in B.C. over the last 10-100 years. What remains of these occurrences is heavily altered by invasion of exotic grasses and shrubs. The populations on Vancouver Island are now severely fragmented and so remote from populations elsewhere that there is no reasonable likelihood of genetic exchange. A population decline of more than 80% is predicted in the next five years. In Nanaimo, development of a trailer park has been proposed for a site where the largest known population occurs (Fairbarns et al. 2004). |
| Long-Term Trend: | A = Decline of >90% |
| Comments: | An estimated 95% of the potential habitat for this species has been lost over the past century due to agricultural, urban, and industrial development, fire suppression, and invasion of exotic grasses and shrubs. In the Victoria area, habitat has decreased from about 10,000 ha in 1800 to about 500 ha in 1997. The species' adaptation to dry prairie and savanna maintained in part by Aboriginal burning practices suggests that it may have been more widespread in southern Vancouver Island before European settlement. Presumably, the species did not begin to decline until after 1850 when fire suppression, grazing, agriculture, and exotic vegetation began to have an impact. |
| Other Factors | |
| Intrinsic Vulnerability: | A=Highly vulnerable |
| Comments: | Epilobium densiflorum is limited by its ability to disperse to new sites. Its seeds lack the coma and obovoid flattened shape that helps dispersal in other members of the genus; therefore, its ability to spread and colonize new sites is severely limited (Fairbarns et al. 2004). The species has been reported as predominantly autogamous (self-pollinated), and ovules may be fertilized by pollen from the same flower. This may diminish genetic diversity within populations and limit the species' ability to adapt to changing environmental conditions. |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | Epilobium densiflorum occurs only in vernally moist meadows and roadsides. Climatic and edaphic factors limit the distribution of this species in B.C. |
| Other Rank Considerations: | None. |
| Information Gaps | |
| Research Needs: | The reproductive biology and ecology of Epilobium densiflorum need further study to resolve conflicting reports of autogamy and outcrossing in this species. |
| Inventory Needs: | Habitat and the extent of Epilobium densiflorum on Vancouver Island have been studied intensively over the past 20 years, but it may be advisable to search meadow communities around the fringes of urban and agricultural areas rather than fragmented islands of habitat within a matrix of human developments. Fringe areas sometimes contain relictual stands of native vegetation that are more extensive and in better condition than areas closer to urban centres like Victoria. For one reason or another, these areas are less suited to development and provide a safe haven. |
| Stewardship | |
| Protection: | Approval of the proposed trailer park in Nanaimo should be denied or delayed until Epilobium densiflorum is listed as endangered by the federal government. The site should be acquired by a conservation buyer, public agency, or land trust and managed for the protection of the species. Epilobium densiflorum could be reintroduced at Somenos Creek where it once occurred. The site was purchased by the Province in order to establish a protected area, but it has not yet been designated as such. |
| Management: | The population of Epilobium densiflorum at Craigflower Meadows in Thetis Lake Regional Park is the only occurrence on protected land. Its habitat needs to be managed to ensure viability of the population; the most immediate threat to it is competition from woody species. Invading Crataegus monogyna and Alnus rubra, as well as Abies grandis, which was planted by the City of Victoria, need to be removed or E. densiflorum will be shaded out by these larger species. Occurrences of E. densiflorum may also be restored or enhanced by reintroduction of the species to protected sites where it may be managed properly. Similarities in habitat suggest that seeds from U.S. populations may be relatively well adapted to site conditions where Canadian populations occur. Thus, one management option might be to consider reintroduction of plants to increase known populations or establish them where they once occurred. |
| Version | |
| Author: | J.A. Christy and M. Donovan |
| Date: | April 28, 2010 |
| References | |
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Batten, R. 2018. Vascular plant GeoCAT range extent and index of AOO maps supporting status assessment 2017_18 for British Columbia Conservation Data Centre. March 2018. Victoria, BC. 450 pp.
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COSEWIC 2005j. COSEWIC assessment and status report on the dense spike-primrose Epilobium densiflorum in Canada. Comm. on the Status of Endangered Wildl. in Can. Ottawa. vi + 26 pp.(www.sararegistry.gc.ca/status/status_e.cfm).
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Fairbarns, M., B. Costanzo, A. Ceska and O. Ceska. 2004. COSEWIC Status report on Dense Spike-primrose, Epilobium densiflorum, in Canada. Unpubl. rep. submitted to the Comm. on the Status of Endangered Wildl. in Can. Ottawa. 24 pp.
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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. 2010. Conservation Status Report: Epilobium densiflorum. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 8, 2026).