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Iris tenuis

S. Wats.

Clackamas Iris

G2Imperiled Found in 4 roadless areas NatureServe Explorer →
G2ImperiledGlobal Rank
UnknownThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.130891
Element CodePMIRI09100
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single state or province
KingdomPlantae
PhylumAnthophyta
ClassMonocotyledoneae
OrderLiliales
FamilyIridaceae
GenusIris
Synonyms
Rodionenkoa tenuis(S. Watson) M.B. Crespo, Mart.-Azorín and Mavrodiev
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 Date2025-05-29
Change Date2025-05-29
Edition Date2025-05-29
Edition AuthorsFredricks, N.A. (1988), rev. N. Dunkirk and N. Ventrella (2025)
Threat ImpactUnknown
Range Extent250-1000 square km (about 100-400 square miles)
Number of Occurrences6 - 20
Rank Reasons
Iris tenuis is a perennial forb occurring in moist, leafy understories of Douglas fir and dense shrub cover known only from a limited region of the Cascade Range of northern Oregon, where it occurs along tributaries of the Clackamas and Molalla rivers in Clackamas County and near Evans Creek in adjacent Marion County. There are an estimated nineteen occurrences of this species, which are potentially threatened by herbicide application along roadsides, wildfire, and climate change, though the scope and severity of threats are unknown. In addition, trends and abundance of this species are not well documented, and monitoring populations is important to improving our understanding of the status of Iris tenuis .
Range Extent Comments
Iris tenuis occurs in the western United States, where it is restricted to the Cascade Range of northern Oregon, along tributaries of the Clackamas and Molalla rivers in Clackamas County, and near Evans Creek in adjacent Marion County (Lenz 1959, Meyers et al. 2015). Range extent was estimated using herbarium specimens and photo-based observations documented between 1985 and 2025 (GBIF 2025, iNaturalist 2025, RARECAT 2025, SEINet 2025).
Occurrences Comments
By applying a 1 km separation distance to herbarium records and photo-based observations documented between 1985 and 2025, there are estimated to be nineteen occurrences rangewide (GBIF 2025, iNaturalist 2025, RARECAT 2025, SEINet 2025).
Threat Impact Comments
Although threats are not widely documented, many populations of Iris tenuis occur on roadsides, according to satellite imagery, and may be impacted by herbicide spraying on roadcuts (Dunkirk 2025, RareCat 2025). The majority of populations also occur in places which have experienced recent wildfires, such as the Riverside and Beachie Creek wildfires of 2020 (Wildland Fire Management Research, Development, and Application Program 2025), though it is unknown if populations experienced impacts from these events and/or from associated fire suppression activities. Climate change will likely raise temperatures and alter the timing and amount of precipitation across the range of this species. Mean annual temperatures in the Mount Hood National Forest region have increased by 1.2 to 1.4 ºC since 1895 and are projected to increase up to 4.5 ºC above historical temperatures by 2099 (Halofsky et al. 2022).
Ecology & Habitat

Habitat

Iris tenuis occurs on "open, wooded slopes in leafy soil with Douglas fir and dense shrubs" from 100-1000 m in elevation (FNA 2002, Meyers et al. 2015), and is often found in moist, cool, shady places with leaf mold (Lenz 1959).
Terrestrial Habitats
Forest/WoodlandForest - Conifer
Other Nations (1)
United StatesN2
ProvinceRankNative
OregonS2Yes
Threat Assessments
ThreatScopeSeverityTiming
7 - Natural system modificationsUnknownUnknownUnknown
7.1 - Fire & fire suppressionUnknownUnknownUnknown
7.1.1 - Increase in fire frequency/intensityUnknownUnknownUnknown
9 - PollutionPervasive - largeUnknownLow (long-term)
9.3 - Agricultural & forestry effluentsPervasive - largeUnknownLow (long-term)
9.3.3 - Herbicides and pesticidesPervasive - largeUnknownLow (long-term)
11 - Climate change & severe weatherPervasive (71-100%)UnknownHigh (continuing)
11.3 - Temperature extremesPervasive (71-100%)UnknownHigh (continuing)

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Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)No
Roadless Areas (4)
Oregon (4)
AreaForestAcres
Bull Of The WoodsMt. Hood National Forest8,843
ElkhornWillamette National Forest9,380
Opal CreekWillamette National Forest5,417
Roaring RiverMt. Hood National Forest27,316
References (14)
  1. <div>Meyers, S.C., T. Jaster, K. E. Mitchell, and L.K. Hardison, editors. 2015. Flora of Oregon. Volume 1: Pteridophytes, Gymnosperms, and Monocots. Botanical Research Institute of Texas, Fort Worth, TX. 608 pp.</div>
  2. Dunkirk, N. 2025. Oregon state rank assessment for Clackamas iris (<i>Iris tenuis</i>). Oregon Biodiversity Information Center. Institute for Natural Resources, Portland State University, Portland, OR.
  3. Flora of North America Editorial Committee (FNA). 2002a. Flora of North America north of Mexico. Vol. 26. Magnoliophyta: Liliidae: Liliales and Orchidales. Oxford Univ. Press, New York. xxvi + 723 pp.
  4. Foster, R.C. 1937. A cytotaxonomic survey of the North American species of Iris. Contr. Gray Herb. 119. 82pp.
  5. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  6. Halofsky, J.E., Peterson, D.L. and A. Rebecca. 2022. Climate Change Vulnerability and Adaptation in the Columbia River Gorge National Scenic Area, Mount Hood National Forest, and Willamette National Forest. General Technical Report PNW-GTR-1001. U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Portland, OR. 469 pp.
  7. iNaturalist. 2025. Online. Available: https://www.inaturalist.org (accessed 2025).
  8. 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.
  9. Lenz, L.W. 1959. <i>Iris Tenuis</i> S Wats., a new transfer to the subsection Evansia. Aliso: A Journal of Systematic and Floristic Botany 4(2): 311-319.
  10. <p>NatureServe's Rapid Analysis of Rarity and Endangerment Conservation Assessment Tool (RARECAT). 2025. Version: 2.1.1 (released April 04, 2025).</p>
  11. Southwest Environmental Information Network (SEINet). 2025. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2025).
  12. Starker, Carl. 1935. <i>Iris tenuis</i>. American Iris Society Bulletin 55: 90-91.
  13. U.S. Geological Survey (USGS). 2024. Gap Analysis Project (GAP) Protected Areas Database of the United States (PAD-US) 4.0: U.S. Geological Survey data release. Online. Available: https://doi.org/10.5066/P96WBCHS (accessed 2025).
  14. Wildland Fire Management Research, Development, & Application Program. 2025. InterAgencyFirePerimeterHistory All Years (1900-2023) [data set]. National Interagency Fire Center (NIFC). https://data-nifc.opendata.arcgis.com/datasets/e02b85c0ea784ce7bd8add7ae3d293d0_0/explore