BC Conservation Data Centre: Species Summary
Epilobium densiflorum
dense spike-primrose
| Scientific Name: | Epilobium densiflorum (Lindley) P. Hoch & Raven | ||||||||||
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| Scientific Name Synonyms: |
Boisduvalia densiflora
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| English Name: | dense spike-primrose | ||||||||||
| Classification / Taxonomy | |||||||||||
| Scientific Name - Concept Reference: | Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR. | ||||||||||
| Classification Level: | Species | ||||||||||
| Species Group: | Vascular Plant | ||||||||||
| Species Code: | EPILDEN | ||||||||||
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| Conservation Status / Legal Designation | |||||||||||
| Global Status: | G5 (Mar 2025) | ||||||||||
| Provincial Status: | S2 (Apr 2019) | ||||||||||
| BC List: | Red | ||||||||||
| Provincial FRPA list: | |||||||||||
| Provincial Wildlife Act: | |||||||||||
| COSEWIC Status: | Endangered (May 2005) | ||||||||||
| SARA Schedule: | 1 - Endangered (Aug 2006) | ||||||||||
| General Status Canada: | 1 - At Risk (2010) | ||||||||||
| Ecology & Life History | |||||||||||
| General Description: | Dense Spike-primrose is an annual with simple or branched stems that are 5-30 cm high. The sessile lower leaves are narrowly lance-shaped and 15-30 mm long with entire or sparsely-toothed margins, while the upper leaves are shorter and broader. Foliage is covered with soft, white, short or long hairs and may also be glandular. Flowers are borne in the axils of the upper leaves in dense spike-like inflorescences at the branch tips. Each flower has 4 pink to purple, 2-lobed petals, 2-8 mm long, and a 4-lobed calyx borne on top of the seed-bearing ovary. The 4-celled ovaries develop into straight, club-shaped capsules, 6-10 mm long, with 12-24 naked seeds. | ||||||||||
| Technical Description: | |||||||||||
| Diagnostic Characteristics: | B. GLABELLA, the other member of this genus in our area, has petals 1.5-4 mm long and capsules that are slightly curved with 24-56 seeds. Species of GAYOPHYTUM have 2-celled ovaries, EPILOBIUM have seeds with tufts of hair at the tips, and CLARKIA have stalked flowers. | ||||||||||
| Subspecies Comments: | None. | ||||||||||
| Identification Comments: | Epilobium densiflorum is an annual taprooted herb. Stems are 15-100 cm tall, simple or branched above, peeling below. Plants are densely white-hairy to long, soft- or stiff-hairy, sometimes glandular. Leaves are alternate except near the base, lanceolate, becoming narrowly ovate in the inflorescence, 1-8.5 cm long, entire or remotely fine-toothed, upper ones hairy; unstalked or nearly so. Flowers in a crowded inflorescence of densely leafy terminal and lateral spikes; hypanthium 1.5-4 mm long; petals 3-10 mm long, white to rose-purple and notched at the tip. Sepals 2-9 mm long. Stigmas generally entire, rarely 4-lobed. Fruits are capsules more or less spindle shaped, long-hairy, 0.4-1.1 cm long, very short-beaked, 4-chambered. Seeds 3-6 per chamber, flat, 1.2-2 mm long, netted, glabrous, brown, and lack the tuft of hairs present in most species of Epilobium. | ||||||||||
| Similar Species: | Epilobium densiflorum may be mistaken for Epilobium torreyi, another rare species in British Columbia. The two species may occur together. E. desiflorum is distinguished from E. torreyi by its shorter petals, crowded inflorescence, lanceolate to ovate leaves, often ashy strigose or glandular hairs, and fruits with the septa free from the valves. | ||||||||||
| Global Reproduction Comments: | Unlike many Epilobium species, Epilobium densiflorum does not have a tuft of hairs on the seed to facilitate wind dispersal (FNA 2021). | ||||||||||
| Provincial Reproduction Comments: | Epilobium densiflorum is predominantly self-pollinated, but pollen may be transferred by bees and syrphid flies. Unlike most species of Epilobium that produce seeds with a tuft of hairs (coma), which help dispersal, E. densiflorum has no coma, and dispersal is very limited. | ||||||||||
| Provincial Ecology Comments: | Historically, the habitat of Epilobium densiflorum was maintained by Aboriginal burning practices, probably on an annual basis. In the absence of burning, invading woody plants and exotic grasses and herbs may be shading out E. densiflorum, competing for resources, or preventing the recruitment of seedlings necessary for the maintaining the species' populations. E. densiflorum's ability to tolerate high moisture levels in winter and spring and very low moisture levels in summer allows it to grow where many other plants cannot survive. | ||||||||||
| Habitats: (Type / Subtype / Dependence) |
Grassland/Shrub / Meadow / Facultative - frequent use
Other Unique Habitats / Garry Oak Vernal Pool / Facultative - frequent use |
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| Global Habitat Comments: | Epilobium densiflorum grows in vernally wet places, moist pastures, woodlands, meadows, along streams and ditches, alluvial valleys, often on low ground in volcanic or sandy soils (FNA 2021). | ||||||||||
| Provincial Habitat Comments: | In British Columbia, Epilobium densiflorum occurs on southeastern Vancouver Island in open meadows and ditches that are moist in spring and very dry in summer. Shallow soils over rock outcrops are often present in meadow habitats in the dry Coastal Douglas-fir zone, but they are too dry to sustain E. densiflorum. It appears that suitable soil conditions occur only in a small fraction of the landscape where the soil is too wet in the winter to allow woody species to flourish but too dry in the summer to support wetland species. Habitats in other parts of the species' range in western North America include vernally wet sites around pools or streams that are subject to summer droughts. An estimated 95% of potential habitat in B.C. has been lost over the past century due to agricultural, urban, and industrial development, fire suppression, and invasion of exotic grasses and shrubs. | ||||||||||
| Provincial Phenology: (1st half of month/ 2nd half of month) |
Jan: Germinating / Germinating
Feb: Germinating / Germinating Mar: Germinating / Germinating Apr: Vegetative / Vegetative May: Vegetative / Vegetative Jun: Vegetative / Vegetative, Flowering Jul: Flowering / Flowering Aug: Flowering, Fruiting / Fruiting Sep: Fruiting / Fruiting |
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| Provincial Phenology Comments: | Epilobium densiflorum is an annual that flowers and fruits in mid to late summer. The seeds are dispersed from loculicidal capsules in the late fall and winter. The seeds germinate during the wet winter or spring, but the plant continues to develop well into the summer drought period that is characteristic of southeast Vancouver Island. | ||||||||||
| Elevation (m) (min / max): | Provincial: 7 / 305 | ||||||||||
| Known Pests: | |||||||||||
| Pollen Vector: | |||||||||||
| Pollinator: | |||||||||||
| Dispersal: | |||||||||||
| Provincial Inventory | |||||||||||
| Inventory Priority: | B - Strong | ||||||||||
| Ownership of occurrences (Known locations): | Mostly private | ||||||||||
| Inventory Need: | Habitat and 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. | ||||||||||
| Inventory Comments: | Suitable sites have been surveyed repeatedly since the early 1980s in a series of projects designed to document the distribution of rare plants in open meadows of southeast Vancouver Island and the Gulf Islands. Over 1000 ha of suitable habitat in over 80 sites have been surveyed, much of it more than once. During the past decade, over 500 person-days have been spent searching for rare species in suitable habitats. This includes two searches specifically for Epilobium densiflorum (approximately 10 person-days in 2001 and 8 person-days in 2003). Despite this concentrated effort, only four populations were found. | ||||||||||
| Economic Attributes | |||||||||||
| Provincial Economic Comments: | No commercial or traditional uses are known for this species. | ||||||||||
| Distribution | |||||||||||
| Endemic: | N | ||||||||||
| Global Range Comment: | Epilobium densiflorum is native to western North America from southern British Columbia to northern Baja California. Most occurrences are found in California and Oregon with scattered observations in Nevada, Arizona, Montana, and Idaho. Range extent was estimated using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1994 and 2025 (RARECAT 2024, GBIF 2025, iNaturalist 2025, NatureServe 2025, SEINet 2025). | ||||||||||
| Disjunct, more common elsewhere: | N | ||||||||||
| Peripheral, major distribution elsewhere: | Y | ||||||||||
| Authors / Contributors | |||||||||||
| Global Information Author: | JM (1994), rev. Johnson, J. (2025) | ||||||||||
| Last Updated: | Mar 27, 2025 | ||||||||||
| Provincial Information Author: | Christy, J.A. | ||||||||||
| Last Updated: | Feb 07, 2005 | ||||||||||
| Last Literature Search: | |||||||||||
| References and Related Literature | |||||||||||
B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC. |
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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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Costanzo, B. 2002b. Stewardship Account for Dense Spike-primrose Epilobium densiflorum. Prepared for the B.C. Conservation Data Centre and the Garry Oak Ecosystems Recovery Team. Sponsored by the Habitat Stewardship Program, Gov. Can., and Nat. Conservancy Can. Victoria, BC. 8 pp. |
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Douglas, G.W., D. Meidinger, and J. Penny. 2002. Rare Native Vascular Plants of British Columbia, 2nd ed. B.C. Conserv. Data Centre, Terrestrial Inf. Branch, Victoria. 358pp. |
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Douglas, G.W., D. Meidinger, and J. Pojar. eds. 1999. Illustrated Flora of British Columbia, Vol. 3, Dicotyledons (Diapensiaceae through Onagraceae). B.C. Minist. Environ., Lands and Parks, and B.C. Minist. For., Victoria. 423pp. |
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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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Raven, P. H. and D. M. Moore. 1965. A revision of BOISDUVALIA (ONAGRACEAE). Brittonia 17:238-254. |
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Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.
Suggested Citation:
B.C. Conservation Data Centre. 2025. Species Summary: Epilobium densiflorum. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 13, 2026).