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Epilobium siskiyouense

(Munz) Hoch & Raven

Siskiyou Willowherb

G3Vulnerable Found in 8 roadless areas NatureServe Explorer →
G3VulnerableGlobal Rank
High - mediumThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.147998
Element CodePDONA06100
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single nation
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderMyrtales
FamilyOnagraceae
GenusEpilobium
Synonyms
Epilobium obcordatum ssp. siskiyouenseMunz
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.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-02-27
Change Date1991-02-08
Edition Date2025-02-24
Edition AuthorsVrilakas, Sue; R. Bittman (2005), rev. C. Nordman (2025).
Threat ImpactHigh - medium
Range Extent5000-20,000 square km (about 2000-8000 square miles)
Number of Occurrences6 - 80
Rank Reasons
Siskiyou Willowherb (Epilobium siskiyouense) occurs in western North America, in alpine and subalpine areas of the Pacific Northwest of the United States, in the central and eastern Klamath Ranges of southwestern Oregon and northern California, in southern Jackson County, Oregon south to Shasta, Trinity and Siskiyou counties, California. It occurs in small montane areas which are rocky and may be wet, often on serpentine. It is estimated that there are about 20 and between 6 and 80 occurrences, some on the Rouge River National Forest, Klamath National Forest, including within the Marble Mountain Wilderness, Siskiyou Wilderness and on Shasta-Trinity National Forest, including within the Mount Eddy Research Natural Area and the Salmon-Trinity Alps Wilderness Area. There are 15 occurrences in California which are considered to have good or excellent viability. Threats to Siskiyou Willowherb (Epilobium siskiyouense) mostly are low and include recreation impacts related to trails or off trail hiking, mining, cattle grazing, development for residential, tourism, for skiing and other recreation, road building, drought, and decline of snowpack as may be exacerbated by climate change.
Range Extent Comments
Siskiyou Willowherb (Epilobium siskiyouense) occurs in western North America, in alpine and subalpine areas of the Pacific Northwest of the United States, in the central and eastern Klamath Ranges of southwestern Oregon and northern California, in southern Jackson County, Oregon south to Shasta, Trinity and Siskiyou counties, California. Range extent was estimated to be 6150 square kilometers, using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1994 and 2025 (CCH2 2025, CNDDB 2025, Colwell and Sims 2020, FNA 2021, GBIF 2025, Jepson Flora Project 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2024, SEINet 2025).
Occurrences Comments
By applying a 1 km separation distance to hit is estimated that there are about 20 and between 6 and 80 occurrenceserbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, of Epilobium siskiyouense rangewide. Most occurrences are in California (CCH2 2025, CNDDB 2025, GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2024, SEINet 2025).
Threat Impact Comments
The various threats known for Siskiyou Willowherb (Epilobium siskiyouense) mostly have low impact to this plant. Threats to Siskiyou Willowherb (Epilobium siskiyouense) include recreation impacts related to trails or off trail hiking, mining, cattle grazing, development for residential, tourism, for skiing and other recreation, road building, drought, and decline of snowpack as may be exacerbated by climate change (CNDDB 2025). One of the Oregon populations is next to the Pacific Crest Trail but recreational hiking and hiking trails have not been considered a high impact threat to this species.
Ecology & Habitat

Habitat

This species grows in open montane (often serpentine) areas, such as outcrops, scree, talus slopes, moist rocky slopes, moist ledges, serpentine ridges, stream banks, mostly (but not always) on Serpentine, also on Perioditite and Granite at elevations of 1600 - 2500 meters (CNDDB 2025, FNA 2021, Jepson Flora Project 2025), in sparsely vegetated rocky sites including sparse woodlands and krummholz forests at, above or below the treeline (Colwell and Sims 2020). The total area of occupied habitat is very small, about 4 hectares (10 acres) in Oregon and 430 hectares (1060 acres) in California, as of 2005 (NatureServe 2025). It is considered a Facultative Wetland (FACW) plant, one which usually occurs in wetlands, but may occur in non-wetland locations. Associated conifer trees include Pinus monticola, Abies magnifica var. shastensis, Pinus balfouriana, and Tsuga mertensiana. Commonly associated herbaceous species include Achillea millefolium, Anemone drummondii, Elymus elymoides, Eriogonum umbellatum, Festuca idahoensis, Minuartia nuttallii subsp. gregaria, Phlox diffusa, Polygonum davisiae, Polystichum lemmonii, Potentilla fruticosa, Sedum kiersteadiae or other Sedum species, and another rare species, Veronica copelandii (CNDDB 2025, Colwell and Sims 2020).

Reproduction

This species flowers from July to September. The seeds are small, with a tuft of hair which promotes wind dispersal which is typical of various plants in the genus Epilobium (Colwell and Sims 2020, Jepson Flora Project 2025).
Terrestrial Habitats
Woodland - ConiferShrubland/chaparralGrassland/herbaceousAlpineBare rock/talus/scree
Palustrine Habitats
HERBACEOUS WETLANDRiparian
Other Nations (1)
United StatesN3
ProvinceRankNative
OregonS2Yes
CaliforniaS3Yes
Threat Assessments
ThreatScopeSeverityTiming
1 - Residential & commercial developmentSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
1.1 - Housing & urban areasSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
1.3 - Tourism & recreation areasSmall (1-10%)Moderate or 11-30% pop. declineHigh (continuing)
2 - Agriculture & aquacultureRestricted - smallModerate or 11-30% pop. declineHigh (continuing)
2.3 - Livestock farming & ranchingRestricted - smallModerate or 11-30% pop. declineHigh (continuing)
3 - Energy production & miningSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
3.2 - Mining & quarryingSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
4 - Transportation & service corridorsSmall (1-10%)Moderate or 11-30% pop. declineHigh (continuing)
4.1 - Roads & railroadsSmall (1-10%)Moderate or 11-30% pop. declineHigh (continuing)
11 - Climate change & severe weatherLarge (31-70%)Moderate - slightHigh (continuing)

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Plant Characteristics
DurationPERENNIAL, SUMMER-FLOWERING
Economic Value (Genus)No
Roadless Areas (8)
California (8)
AreaForestAcres
Castle Crags AShasta-Trinity National Forest113
Castle Crags BShasta-Trinity National Forest1,619
KangarooKlamath National Forest40,617
Lake EleanorShasta-Trinity National Forest397
Mt. EddyShasta-Trinity National Forest7,232
Orleans Mtn.Klamath National Forest49,090
SnoozerKlamath National Forest23,414
Weaver BallyShasta-Trinity National Forest829
References (9)
  1. California Natural Diversity Database (CNDDB). 2025. RareFind Version 5.3.0. California Department of Fish and Game, Sacramento.
  2. CCH2 Portal. 2025. Consortium of California Herbaria. Online. Available: https//:www.cch2.org/portal/index.php (Accessed 2025).
  3. Colwell, A. and A.E. Sims . 2020. Species Account: <i>Epilobium siskiyouense</i>. CNPS Rare Plant Inventory, California Native Plant Society. Online. Available: https://rareplantfiles.cnps.org/scc/EpilobiumSiskiyouenseSpAcctSCC20201103.pdf (accessed 2025).
  4. Flora of North America Editorial Committee (FNA). 2021. Flora of North America north of Mexico. Vol. 10. Magnoliophyta: Proteaceae to Elaeagnaceae. Oxford Univ. Press, New York. xxiv + 456 pp.
  5. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  6. Jepson Flora Project (eds.) 2025. Jepson eFlora. Online. Available: https://ucjeps.berkeley.edu/eflora/ (accessed 2025).
  7. 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.
  8. NatureServe. 2025. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  9. Southwest Environmental Information Network (SEINet). 2025. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2025).