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Streptanthus howellii

S. Wats.

Howell's Jewelflower

G2Imperiled (G2G3) Found in 4 roadless areas NatureServe Explorer →
G2ImperiledGlobal Rank
High - lowThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.152527
Element CodePDBRA2G0N0
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single nation
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderCapparales
FamilyBrassicaceae
GenusStreptanthus
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 Date2025-02-05
Change Date2013-06-07
Edition Date2025-02-05
Edition AuthorsKagan, J., S. Vrlikas, & K. Maybury (1996), rev. C. Nordman (2013), Johnson, J. (2025)
Threat ImpactHigh - low
Range Extent1000-5000 square km (about 400-2000 square miles)
Number of Occurrences21 - 80
Rank Reasons
Streptanthus howellii is endemic to southwestern Oregon and adjacent northwestern California and restricted to serpentine soils. It is only known from about 35, mostly small populations. With natural fires, this species would probably be locally abundant, but lack of fire has caused declines in populations.
Range Extent Comments
Streptanthus howellii is strictly endemic to serpentine in the Siskiyou Mountains of northwestern California and southwestern Oregon, in Del Norte County, CA and Curry and Josephine Counties, OR . The total range extent including historic records is 2400 km sq and the range based on herbarium specimens, photo-based observations, and NatureServe network occurrence data collected between 1994 and 2025 is 1100 km sq (GBIF 2025, iNaturalist 2025, NatureServe 2025, CNDDB 2025, SEINet 2025, OSU 2025). Historical reports from Siskiyou County, California, may be based on vague location information referring to the Siskiyou Mountains.
Occurrences Comments
By applying a 1 km separation distance to herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, it is estimated that there are more than 300 occurrences rangewide (GBIF 2025, iNaturalist 2025, NatureServe 2025, CNDDB 2025, SEINet 2025, OSU 2025).
Threat Impact Comments
Threats to Streptanthus howellii include changes in fire return interval, mining, and roads (NatureServe 2025, CNDDB 2025).
Ecology & Habitat

Description

Perennial plant, usually with unbranched glaucous (whitish and pale purple) stems. The leaves are somewhat fleshy, and are rounded at the tips with petioles. The flowers are maroon to purple, the fruits are long and narrow, 3 mm wide and 6-12 cm long (Flora of North America Editorial Committee 2010).

Habitat

Streptanthus howellii grows in serpentine chaparal and open conifer-hardwood forests from low elevation, rocky flats to montane ridges and summits, sometimes on road cuts. It is usually in open, exposed, serpentine clay, but will persist in open, brushy woodlands and brushfields for years (FNA 2010, OSU 2025, CNDDB 2025).

Reproduction

Flowers from June to July (FNA 2010).
Terrestrial Habitats
Forest/WoodlandForest EdgeWoodland - MixedShrubland/chaparralBarrens
Other Nations (1)
United StatesN2
ProvinceRankNative
CaliforniaS2Yes
OregonS2Yes
Threat Assessments
ThreatScopeSeverityTiming
3 - Energy production & miningRestricted - smallModerate or 11-30% pop. declineHigh - moderate
3.2 - Mining & quarryingRestricted - smallModerate or 11-30% pop. declineHigh - moderate
4 - Transportation & service corridorsSmall (1-10%)Serious or 31-70% pop. declineHigh - moderate
4.1 - Roads & railroadsSmall (1-10%)Serious or 31-70% pop. declineHigh - moderate
7 - Natural system modificationsLarge - restrictedSerious - moderateHigh - moderate
7.1 - Fire & fire suppressionLarge - restrictedSerious - moderateHigh - moderate

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Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)No
Roadless Areas (4)
California (3)
AreaForestAcres
KellySix Rivers National Forest5,195
North Fork SmithSix Rivers National Forest37,898
PacksaddleSix Rivers National Forest3,862
Oregon (1)
AreaForestAcres
South KalmiopsisSiskiyou National Forests104,477
References (12)
  1. California Natural Diversity Database (CNDDB). 2025. RareFind Version 5.3.0. California Department of Fish and Game, Sacramento.
  2. Flora of North America Editorial Committee (FNA). 2010. Flora of North America north of Mexico. Vol. 7. Magnoliophyta: Salicaceae to Brassicaceae. Oxford University Press, New York. xxii + 797 pp.
  3. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  4. iNaturalist. 2025. Online. Available: https://www.inaturalist.org (accessed 2025).
  5. 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.
  6. Meinke, R.J. 1982. Threatened and Endangered Vascular Plants of Oregon: An Illustrated Guide. U.S. Fish and Wildlife Service, Region 1, Portland, Oregon. 326 pp.
  7. NatureServe. 2025. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  8. Oregon State University (OSU). 2025. Oregon Flora website. Oregon State University Herbarium at Oregon State University. Online. Available: https://oregonflora.org/ (accessed 2025).
  9. Peck, M.E. 1961. A manual of the higher plants of Oregon. 2nd edition. Binsford & Mort, Portland, Oregon. 936 pp.
  10. Rollins, R.C. 1993a. The Cruciferae of continental North America: Systematics of the mustard family from the Arctic to Panama. Stanford Univ. Press, Stanford, California. 976 pp.
  11. Safford, H. D., J. H. Viers, and S. P. Harrison. 2005. Serpentine endemism in the California flora: A database of serpentine affinity. Madroño 52(4): 222-257.
  12. Southwest Environmental Information Network (SEINet). 2025. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2025).