Bitterroot Milkvetch

Hesperonix scaphoides (M. E. Jones) Rydberg
Astragalus arrectus scaphoides M. E. Jones. Proc. Calif. Acad. II. 5: 664. 1895. Astragalus scaphioides [err. I Rydb. Mem. N. Y. Bot. Gard. 1: 241. 1900. Astragalus scaphoides M. E. Jones. Contr. W. Bot. 10: 69. 1902. Phacopsis scaphoides Rydb. Bull. Torrey Club 40: 52. 1913.
A perennial, with a thick woody root and cespitose caudex; stems many, 3-,5 dm. high, erect, angled and slightly sulcate, sparingly strigose; leaves ascending, 8-10 cm. long, the rachis sulcate, strigose; stipules deltoid, acuminate, strigose, 3-5 mm. long; leaflets elliptic to obovate, 1-1.5 cm. long, 4—7 mm. wide, rounded at the apex, glabrous above, strigose beneath; peduncles 5-10 cm. long, sulcate; racemes 4-8 cm. long; bracts subulate, 3 mm. long, blackhairy; calyx black-hairy, the tube 6-7 mm. long, the teeth subulate, 2 mm. long; corolla unknown; pod leathery, stipitate; stipe 1-1.5 cm. long, slightly curved upwards, the body erect, glabrous, slightly reticulate, oblong, about 2 cm. long, 7 mm. thick and 5 mm. wide, truncate or subcordate at the base, acute at the apex, slightly sulcate on both sutures, somewhat broadly ^-shaped in cross-section.
Type locality: West of Clark's Canon, Beaverhead County, Montana. Distribution: Montana and Idaho.

Perennial, Herbs, Stems woody below, or from woody crown or caudex, Taproot present, Nodules present, Stems erect or ascending, Stems less than 1 m tall, Stems solid, Stems or young twigs sparsely to densely hairy, 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, Inflorescence axillary, Bracts very small, absent or caducous, Flowers zygomorphic, Calyx 5-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals clawed, Petals white, Petals ochroleucous, cream colored, 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 beaked, Stamens 9-10, Stamens diadelphous, 9 united, 1 free, Filaments glabrous, Style terete, Style persistent in fruit, Fruit a legume, Fruit stipitate, Fruit freely dehiscent, Fruit oblong or ellipsoidal, Fruit rugose wrinkled or reticulate, Fruit or valves persistent on stem, Fruit coriaceous or becoming woody, Fruit exserted from calyx, Fruit beaked, Fruit glabrous or glabrate, Fruit 11-many seeded, Seeds cordiform, mit-shaped, notched at one end, Seed surface smooth, Seeds olive, brown, or black.

Astragalus scaphoides, the bitterroot milkvetch, is a flowering plant in the family Fabaceae, the third-largest plant family in the world. It is found only in a small area of southwest Montana and adjacent parts of Idaho. It grows on shallow, south-facing slopes, in semi-arid sage scrub.

Astragalus scaphoides is a perennial herbaceous plant, with pinnate leaves. The pale yellow flowers open in May and are visited by several species of bumblebees and solitary bees, including species from the genera Osmia and Anthophora.

Plants can be found near Lemhi Pass on the Montana-Idaho border, and near Bannack State Park in Montana.

Plants tend to flower in alternate years, similar to mast years in grasses and trees.