Astragalus tweedyi, or Tweedy's milkvetch, is a perennial herb in the pea family. It is native to Washington and Oregon in the Pacific Northwest of the United States.
Taxonomy Astragalus tweedyi was described and published in 1890 by William Marriott Canby, who named it in honor of Frank Tweedy, one of the first to collect it, in the hills along the Columbia River in Yakima County, Washington Territory in 1883. At the time, he was working as a topographer on the Northern Transcontinental Survey. Canby was head of Economic Botany for the project.
It had been collected by Thomas J. Howell who called it Astragalus collinus. Canby agreed it was closely allied to collinus, but easily distinguished based on leaves and pods, justifying creation of a new species.Canby, W.M. 1890. Astragalus Tweedyi n. sp. in Some Western Plants. Bot. Gaz. 15: 150. Univ Chicago Press JournalsAstragalus in Hitchcock, C.L., and Cronquist, A. 1973. Flora of the Pacific Northwest. U. Washington Press. Tweedy's specimen, the isolectotype, is deposited in Gray Herbarium at Harvard.Astragalus Tweedyi type (in part), Gray Herbarium
Description Astragalus tweedyi is a much-branched sparsely hairy perennial herb to high. Leaves are long, and pinnately-compound with 15-21 narrow leaflets. The flowers are typical pea flowers, with five petals: banner, two wings and a keel. They are creamy in color and ascending on the rachis. The pods are erect at maturity, to long, and circular in cross-section.Abrams, L., and Ferris, R.S. 1940. Illustrated Flora of the Pacific States, Washington, Oregon, and California.
Astragalus tweedyi is similar to A. collinus, but can be distinguished based on flowers and pods, which are ascending to erect in tweedyi and pendulous in collinus.
Distribution and habitat Astragalus tweedyi is endemic to south central Washington and north central Oregon.Astragalus tweedyi in USDA Plants Database It grows on dry, somewhat rocky, hillsides and meadows, from , mostly in a sagebrush-bunchgrass association."Astragalus tweedyi" in NatureServe Explorer
Conservation status Astragalus tweedyi was a candidate species for listing under the United States Endangered Species Act of 1973. It was removed in 1985 because it is more abundant and widespread, and less threatened than previously believed.Federal Register: 50 Fed. Reg. 39073 (Sept. 27, 1985).
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