National Collection of Imperiled Plants

CPC National Collection Plant Profile

Photographer:

Ed Guerrant

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CPC National Collection Plant Profile

Trifolium thompsonii

Family:	Fabaceae
Common Name:	Thompson's clover
Author:	Morton
Growth Habit:	Forb/herb
CPC Number:	4332

Distribution
Protection
Conservation
References

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Photographer: Ed Guerrant
ed.guerrant[at]berrybot.org

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Image Owner: Washington Natural Heritage Program

Trifolium thompsonii is Not Sponsored

Primary custodian for this plant in the CPC National Collection of Endangered Plants is:

University Of Washington Botanic Gardens

Edward Guerrant, Ph.D. contributed to this Plant Profile.

Trifolium thompsonii

Trifolium thompsonii probably doesn't look like any other clover you've ever seen. It grows up to two feet tall and its large, spherical, reddish-lavender flower heads rise above the swaying grass like a sea of cheerleader pom-poms. Unlike most clovers, the leaves of this plant are comprised of 3 to 8 narrow, pointed leaflets (most clovers have three leaflets, hence the name "trifolium" or "three leaves"). It grows only within a fairly limited geographical distribution (only 20 miles north to south), but Trifolium thompsonii can be found in a wide variety of habitats. It grows in open ponderosa pine woods, grass and herb dominated areas, and sagebrush steppe. Steep slopes, along ridgelines, in alluvial fans and along canyon bottoms anywhere from 140 feet to 3760 feet (40m to 1130 m) in elevation are likely places to find this species.

Distribution & Occurrence

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State Range

Washington

Habitat

Trifolium thompsonii grows in a wide variety to habitats. The majority of populations grow on the fringe of the ponderosa pine (Pinus ponderosa) zone in open ponderosa pine woods or grass and herb dominated areas. It grows along ridgelines, on steep slopes, in alluvial fans, and in canyon bottoms anywhere from 140 feet to 2760 feet (40 m to 1130 m).

Distribution

WA: Columbia Basin, Eastern Cascades. Chelan County and Douglas County, WA.

Number Left

Approximately 15 sites have been observed since 1986. Numbers range from as low as 30-40 to as high as several thousand per site. 11 of the known sites are on Forest Service Land (WNHP 2000).

Protection

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Global Rank:	G2	9/30/1997	Guide to Global Ranks
Federal Status:	SC		Guide to Federal Status
Recovery Plan:	No

State/Area Protection

	State/Area	Rank	Status	Date
	Washington	S2	T	10/1/2001

Conservation, Ecology & Research

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Ecological Relationships

Trifolium thompsonii has an unusual growth cycle. Vegetative buds develop in the autumn, when temperatures drop to freezing on a regular basis at night. The buds over-winter and then emerge in the end of March after all the snow melts. Once temperatures rise above freezing (usually in early April), the buds begin to sprout. Flowering begins in mid-May and continues for nearly two months. The first batch of seeds matures by the end of June (WNHP 1999).

Trifolium thompsonii is found primarily in microsites that are intermediate between well exposed, dry, south-facing slopes and more shaded, mesic, and highly vegetated sites (WNHP 1999). Occasional fires may have played an important role in maintaining suitable habitat for Thompson's clover. It is not known why this species has such a varied habitat but such a limited distribution.

Like many other members of the pea family, Trifolium thompsonii is able to form a symbiotic relationship with nitrogen-fixing bacteria. Thus, this plant has an advantage over competing vegetation in soils that are low in available nitrogen (WNHP 1999).

The primary pollinators appear to be a butterfly (Plebejus saepiolus) and several species of bumblebee (Bombus sp.). Long distance pollen transfer may be fairly common between nearby populations. Seed predation can often be very high. In one study, over 14% of observed seeds had some kind of insect boring (Canfield 1977).

Threats

Threats include (in WNHP 1999):
� The invasion of exotic species such as knapweed (Centaurea diffusa) and cheatgrass (Bromus tectorum).
� Agricultural conversion.
� Livestock grazing.
� Illegal ORV use in population areas.

Current Research Summary

� Comprehensive study of the ecological life history of Trifolium thompsonii. Geology, soil characteristics, phenology and morphology, floral biology, seed biology, predation, effects of fire, interactions with cheat grass (Bromus tectorum), population dynamics and effects of cover on the taxon were all investigated (Canfield 1977).
� Germination trials at The Berry Botanic Garden were inconclusive. Seeds were subjected to either 8 weeks of cold stratification or no cold stratification followed by either constant 68�F (20�C) or alternating 50� /68�F (10�/20�C) temperatures. Without cold stratification, both temperature treatments showed 40% germination. With cold stratification, the constant 68�F treatments showed 40% germination while the alternating 50�/68�F treatment showed 80% germination (BBG File).

Current Management Summary

� A proposal was made in 1975 to designate an area to help preserve this taxon. This resulted in the establishment of the Thompson Clover Natural Research Area in 1977 by the U.S. Forest Service.

Research Management Needs

� Search suitable habitats in Douglas and Chelan County for populations (WNHP 1999).
� Study potential factors influencing the limited distribution of Trifolium thompsonii.

Ex Situ Needs

� Collect and store seeds from across the known range. Collect from a variety of habitats and elevations.
� Determine optimum germination conditions. Test conditions corresponding to natural elevation and habitat gradients for this species.
� Determine propagation and reintroduction protocols.

References

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Electronic Sources

WNHP. (2000). Washington Natural Heritage Program Database. Olympia, Washington.

Journal Articles

1933. (Original Publication). Journal of the Washington Academy of Sciences. 23: 270.

Scherer, G.; Zamora, B.; Everett, R. 1996. Habitat characteristics and morphological differences of Trifolium thompsonii populations. Northwest Science. 70, 3: 242-251.

Reports

WNHP. 1999. Field Guide to Selected Rare Vascular Plants of Washington. Produced as part of a cooperative project between the Washington Department of Natural Resources, Washington Natural Heritage Program, and the U.S.D.I. Bureau of Land Management, Spokane District.

Theses

Canfield, J.E. 1977. The ecological life history of Trifolium thompsonii Morton, with reference to its restricted distribution. [Unpublished Masters Thesis]: University of Washington. 145p.

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This profile was updated on 3/4/2010