Astragalus hypoxylus S. Wats.

Hamosa hypoxyla (S. Wats.) Rydb. Bull. Torrey Club 54:336. 1927.
Astragalus hypoxylus S. Wats. Proc. Am. Acad. 18: 192. 1883.
A perennial, with a prostrate branching woody base, and short herbaceous branches of the season, these less than 5 cm. long, minutely strigose; leaves 2-4 cm. long, spreading; stipules distinct, deltoid, strigose, 1-1.5 mm. long; leaflets 9-13, obovate or elliptic, 3-6 mm. long, rounded at the apex, strigose beneath, glabrous above; peduncles 5-7 cm. long; racemes short, spike-like, 1-2.5 cm. long; bracts lanceolate, 1-2 mm. long; calyx strigose, the tube about 2 mm. long, and nearly as broad, the teeth subulate, 2 mm. long; corolla about 6 mm. long; banner obovate, abruptly arcuate; wings nearly as long, the blade oblong; keel-petals much shorter, acute; pod ascending, sessile, about 1 cm. long, 3 mm. wide and as thick, strigose, slightly arcuate, acute on the upper suture, sulcate on the lower, 2-celled, cordate in crosssection.
Type locality': Maloney's Range. Huachuca Mountains, Arizona. Distribution: Known only from the type locality.

Perennial, Herbs, Stems woody below, or from woody crown or caudex, Taproot 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, 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 5-9, 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 glabrous, Petals separate, Corolla papilionaceous, Petals clawed, Petals white, Petals blue, lavander to purple, or violet, Petals bicolored or with red, purple or yellow streaks or spots, Banner peta l 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 indehiscent, Fruit oblong or ellipsoidal, Fruit coriaceous or becoming woody, Fruit exserted from calyx, Fruit beaked, Fruit glabrous or glabrate, Fruit hairy, Fruit 3-10 seeded, Fruit 11-many seeded, Seeds cordiform, mit-shaped, notched at one end, Seed surface smooth, Seeds olive, brown, or black.

Astragalus hypoxylus is a rare species of flowering plant in the legume family known by the common name Huachuca milkvetch, or Huachuca Mountain milkvetch. It is endemic to Arizona in the United States, where it is known only from the Patagonia and Huachuca Mountains. There are three populations.

This small perennial herb forms a patch on the ground no more than about 10 cm (3.9 in) wide and 3 to 4 cm (1.2 to 1.6 in) tall. It grows from a fibrous taproot. The alternately arranged leaves are each made up of several pairs of gray-green leaflets which are a few millimeters long. The inflorescence is a flower cluster about 1 cm (0.39 in) wide containing tiny white flowers with purple tips. The flowers bloom in April and May and are pollinated by bees of the genera Anthophora, Bombus, and Osmia. The fruit is a yellow and purple legume pod about 1 cm (0.39 in). This Astragalus looks so different from other species that it was once classified in a monotypic genus all its own.

This plant grows in woodlands dominated by Emory oak (Quercus emoryi), Mexican blue oak (Q. oblongifolia), alligator juniper (Juniperus deppeana), and Mexican pinyon (Pinus discolor). The substrate is a gravelly soil rich in limestone and metamorphic rock.

Astragalus hypoxylus adalah spesies tumbuhan yang tergolong ke dalam famili Fabaceae. Spesies ini juga merupakan bagian dari ordo Fabales. Spesies Astragalus hypoxylus sendiri merupakan bagian dari genus Astragalus. Nama ilmiah dari spesies ini pertama kali diterbitkan oleh S.Watson.

Astragalus hypoxylus là một loài thực vật có hoa trong họ Đậu. Loài này được S.Watson miêu tả khoa học đầu tiên.