Tygh Valley Milkvetch

Perennial, Herbs, Stems woody below, or from woody crown or caudex, T aproot present, Nodules present, Stems or branches arching, spreading or decumbent, Stems prostrate, trailing, or mat forming, Stems less than 1 m tall, Stems solid, Stems or young twigs sparsely to densely hairy, Stems silvery, canescent, tomentose, cobwebby, or wooly, Leaves alternate, Leaves petiolate, Stipules conspicuous, Stipules membranous or chartaceous, Stipules persistent, Stipules free, Leaves compound, Leaves odd pinnate, Leaf or leaflet margins entire, Leaflets opposite, Leaflets 10-many, Leaves hairy on one or both surfaces, Inflorescences racemes, Inflorescences spikes or spike-like, Inflorescence axillary, Bracts very small, absent or caducous, Flowers zygomorphic, Calyx 5-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals clawed, Petals orange or yellow, Banner petal narrow or oblanceolate, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Keel petals auriculate, spurred, or gibbous, Keel tips obtuse or rounded, not b eaked, Stamens 9-10, Stamens diadelphous, 9 united, 1 free, Filaments glabrous, Style terete, Style persistent in fruit, Fruit a legume, Fruit freely dehiscent, Fruit oblong or ellipsoidal, Fruit enclosed in calyx, Fruit beaked, Fruit glabrous or glabrate, Fruit hairy, Fruit 3-10 seeded, Seeds cordiform, mit-shaped, notched at one end, Seed surface smooth, Seeds olive, brown, or black.

Astragalus tyghensis is a species of flowering plant in the legume family known by the common name Tygh Valley milkvetch. It is endemic to Oregon in the United States, where it is known only from the Tygh Valley of Wasco County.

This species is a perennial herb growing from a stout taproot and a branching caudex. The plant forms mats or clumps, with stems growing prostrate or upright and up to 55 centimeters long. Most of the plant is covered in long, silky hairs. The leaves are divided into a number of leaflets each up to 1.7 centimeters long. The inflorescence is a raceme of up to 40 flowers. Each flower has a calyx of very hairy sepals and a pale yellow corolla up to 1.2 centimeters long. The fruit is a legume pod up to 0.7 centimeters long. The flowers are pollinated by insects, particularly bees, and the plant reproduces by seed.

This species grows in sagebrush, prairie, and grassland habitat, and may occur along roadsides.

This species was a candidate for federal protection by the United States Fish and Wildlife Service. It is now considered a Species of Concern. The plant's habitat has been consumed for agricultural purposes. It also faces competition with noxious weeds, such as Centaurea diffusa.