Kingdom: Plantae

Phylum: Magnoliophyta – flowering plants

Class: Magnoliopsida – Dicotyledons

Family: Asteraceae

Common Name: Palouse thistle

Species Code: CIBR

Origin: An endemic Palouse species native to the meadow-steppe in southeast Washington, northeast Oregon, and adjacent Idaho.

Rare: Ranked S2 (imperiled) in Idaho by the Conservation Data Center but common enough in Washington and Oregon not to be ranked there.

Form: forb, perennial from rhizomes, 30-100 cm tall, branched above or sometimes below the soil surface; short-lived.

Duration: perennial

Longevity: short

Habitat Type: prairie

Wetland Indicator Status: not listed

Leaves: 15-30 cm long, petiolate (upper sessile), green above, white lanulose underneath, coarsely toothed to pinnatifid, the lobes ovate or deltoid; margins with spines 1-3 mm long.

Mature height: 12-40 inches

Flowers: several, borne on the ends of the branches; involucre 2-3.5 mm high, bracts imbricate, with dorsal ridges, the outer bracts spined, the inner ones pointed at the tip; flowers all discoid and perfect, white to cream; receptacle densely bristly.

Flowers color: white

Bloom: June-Aug

Fruit: Achenes 3-5 mm. long, ellipsoid, compressed, smooth, light brown; pappus 20-22 mm long, white.

Characteristics:
Reproduces both sexually by seed and vegetatively by rhizomes.
C. palousense in Piper & Beattie 1914.
Flowers all discoid and perfect.
2n = 22, 26 (Flora of North America Editorial Committee 1993+).
Fruit is an achene.
Seeds have an attached pappus but are fairly large and heavy, so long distance travel by wind is unlikely.
Larva of the Mylitta crescent (Phyciodes mylitta) feed on some species of Cirsium (Pocewicz 2005).
A biocontrol insect (Rhinocyllus conicus) originally introduced to control thistles in the genus Carduus has been found infesting the native Cirsium brevifolium (Gray 1998). For further information on cross-over of biocontrol insects to native thistles see:
Louda & O’Brien 2002.
Louda & Rand 2003.
Louda 1998.
Louda et al 1997.
Strong 1997.

Comments: endemic to the Palouse grasslands in northeast Oregon, southeast Washington, and adjacent Idaho. Considered for federal listing in 1981.

Sun requirement: full

Soil moisture: mesic

Sowing time: fall

Transplant time: spring

Stratification: cold moist stratification appears helpful

Seed yield: low

Seed harvest: difficult

Seed first harvest: second season

Seed cleaning: easy

Planting duration: short

Seed insect problem: yes

Seed shatter: medium

Seed size: medium

Seed harvest date: August

Seed comments: Plants are prickly and difficult to handle. Seed is consumed by several insects.

Herbaria: Specimen data and digital resources from The Consortium of Pacific Northwest Herbaria

Key words: native rare upland thistle

Propagation:
Stratification appears beneficial but sufficient data is not available. It should also be possible to propagate by rhizome cuttings.
Seed insects often cause significant reductions in viable seed production.
Reproduces both sexually by seed and vegetatively by rhizomes.

References:
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 7+ vols. New York and Oxford. Oxford University Press. Online at http://www.fna.org/FNA/

Gray, Karen. 1998. Plant Protection Gone Awry. Sage Notes 20(3):10.

Louda, S.M., D. Kendall, J. Connor, D. Simberloff. 1997. Ecological Effects of an Insect introduced for the Biological Control of Weeds. Science 227: 1088-1090.

Louda, Svata M. 1998. Population Growth of Rhinocyllus conicus (Coleoptera: Curculionidae) on Two Species of Native Thistles in Prairie. Environmental Entomology 27:834-841.

Louda, Svata M. and Tatyana A. Rand. 2003 Native Thistles: Expendable or Integral to Ecosystem Resistance to Invasion? p. 5-15 in: The Importance of Species: Perspectives on Expendability and Triage. Edited by Peter Kareiva and Simon A. Levin. Princeton University Press. Princeton, New Jersey.

Louda, Svata M. and Charles W. O'Brien. 2002. Unexpected Ecological Effects of Distributing the Exotic Weevil, Larinus planus (F.), for the Biological Control of Canada Thistle. Conservation Biology 16:717-727.

Piper, C.V., and R.K. Beattie. 1914. The Flora of Southeastern Washington and Adjacent Idaho. Lancaster, PA: Press of the New Era Printing Company. 296 pp.

Pocewicz, Amy. 2005. Host Plants of Palouse Butterfly Species. 2 page handout to accompany the April 2005 presentation to the Palouse Prairie Foundation.

Strong, Donald R. 1997. Fear No Weevil?. Science 277:1058-1059.

Links:
Plant Profile from the USDA PLANTS Database
Species description from Flora of North America
Species information from the University of Washington Herbarium