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Anderson, Wynn
Astragalus arizonicus
Astragalus arizonicus A. Gray
Arizona Milkvetch
Fabaceae (Pea family)
Synonym(s):
USDA Symbol: ASAR6
USDA Native Status: L48 (N)
"Diffuse, usually slender, perennial but of short duration, sometimes flowering the first season, with a taproot and at length shortly forking caudex or knotty root-crown, strigulose throughout with filiform or largely flattened, straight, appressed (and sometimes a few narrowly ascending) hairs up to 0.4-0.8 (0.9) mm. long, the stems and herbage silvery-canescent or cinereous, rarely greenish- cinereous, the leaflets equally pubescent on both sides or more densely so above than beneath; stems several or numerous, decumbent or prostrate with ascending tips, (0.5) 1.5-4.5 (5) dm. long, simple, branched at base only, or spurred at most axils preceding the first peduncle, flexuous or zigzag distally, together forming loosely woven mats." (bibref: 1814).
"In the early spring months A. arizonicus makes an attractive picture, as it spreads its round mats of silvery foliage, decked with an outer ring of pink- or lavender-purple flowers, over the calcareous gravels between bushes of cat’s-claw acacias, junipers, or sahuaros. Later in the season as the stems elongate and the fruits mature, the plants take on an untidy, withered look and are easily passed by unnoticed." (bibref: 1814).
Plant Characteristics
Duration: PerennialHabit: Herb
Leaf Arrangement: Alternate
Fruit Type: Legume
Size Notes: "Stems several or numerous, decumbent or prostrate with ascending tips, (0.5) 1.5-4.5 (5) dm. long." (bibref: 1814).
Leaf: "Stipules submembranous becoming papery and pallid, ovate- or deltoid-acuminate, or broadly triangular, about semiamplexicaul, pubescent dorsally; leaves 2-8 (10) cm. long, all petioled or the uppermost sometimes subsessile, with (5) 9-15 (17) linear, linear-oblong, -elliptic, narrowly lanceolate, or (when short) narrowly oval, obtuse, mucronulate, or acute, flat or folded leaflets (1.5) 3-17 (21) mm. long." (bibref: 1814).
Flower: "Peduncles erect or divaricate and incurved, (1.5) 2.5-10 (15) cm. long, the lower, more vigorous ones a little longer than the leaf, humistrate in fruit; racemes loosely or at first anthesis rather closely (7) 10- 30-flowered, the flowers ascending, the axis elongating, (1.5) 2.5-10 cm. long in fruit; bracts membranous, ovate, triangular, or lanceolate, 0.8-2 (3) mm. long; pedicels ascending, usually at a narrow angle and straight or nearly so, at anthesis 0.5-1.6 (2) mm., in fruit 1-2.2 mm. long; bracteoles 0-2; calyx (4.5) 5-7 mm. long, strigulose with white or mixed white and black hairs, the symmetric disc 1-1.4 mm. deep, the campanulate tube 3.3-4.1 mm. long, 2.1-3.1 mm. in diameter, the broadly or slenderly subulate teeth (1.2) 1.4-3 mm. long, the whole becoming scarious, ruptured, marcescent; petals dull pink-purple, the banner with a pale, striate eye in the fold, the wing-tips paler or white, or all yellowish tinged with lurid lilac; banner recurved through about 50 degrees, sometimes further in age, obovate-cuneate to suborbicular-flabellate, shallowly notched, (8.7) 9-12 mm. long, (6.1) 6.7-9.1 mm. wide; wings (6.8) 7.1-10 mm. long, the claws (2.4) 2.84 (4.3) mm., the narrowly oblong or oblong-oblanceolate, obtuse, nearly straight blades (4.7) 5-6.5 mm. long, 1.7-2.3 (2.5) mm. wide; keel (0.2-1 mm. longer than the wings, 0.3-2 (2.5) mm. shorter than the banner) 8.2-10.4 mm. long, the claws (2.6) 2.8-4 (4.4) mm., the lunately triangular blades (4.7) 5.2-6.5 mm. long, (1.9) 2.2-2.7 mm. wide, nearly erect in the lower half, thence abruptly incurved through 70-90 degrees and produced into a narrowly triangular, porrect, acute or subacute, beaklike apex; anthers (0.4) 0.45-0.65 (0.7) mm. long." (bibref: 1814).
Fruit: "Pod erect straight or gently incurved, 1.5-3 cm. long, (2.2) 2.5-4 mm. in diameter, cuneate at base, contracted distally into a short, triangular-acuminate, stoutly cuspidate, laterally compressed, unilocular beak, otherwise obtusely triquetrous, bluntly carinate ventrally by the thick suture, the lateral angles rounded, the lateral faces more or less convex at maturity, the dorsal face flattened or very shallowly and openly sulcate (the dorsal suture slender but prominent externally), the thin, densely strigulose valves becoming papery, stramineous, finely elevate-reticulate, inflexed as a complete or nearly complete septum 1.4-3 mm. wide; seeds quadrate, brown or greenish-brown, commonly purple-dotted, pitted and wrinkled but somewhat shining, 1.8-2.6 (3) mm. long." (bibref: 1814).
Bloom Information
Bloom Color: White , Pink , Yellow , Purple , VioletBloom Time: Mar , Apr , May , Jun
Bloom Notes: "Petals dull pink-purple, the banner with a pale, striate eye in the fold, the wing-tips paler or white, or all yellowish tinged with lurid lilac." (bibref: 1814).
Distribution
USA: AZ , NMNative Distribution: "On various soils but apparently most frequent and vigorous on calcareous formations, widespread and rather common in the foothills around and within the upper Gila River Basin, from the head of the Hassayampa to the Salt and San Pedro Rivers, westcentral to southeastern Arizona, and south to the head of the Magdalena River in northern Sonora." (bibref: 1814).
Native Habitat: "Open stony hillsides, alluvial fans, washes, and canyon beds, sometimes abundant on gravelly roadsides, in desert-grassland, thorn scrub, oak scrub, or juniper forest, 2800-4650 feet." (bibref: 1814).
Bibliography
Bibref 1814 - Atlas of North American Astragalus Volume 2 (1964) Barneby, Rupert C.Search More Titles in Bibliography
Additional resources
USDA: Find Astragalus arizonicus in USDA PlantsFNA: Find Astragalus arizonicus in the Flora of North America (if available)
Google: Search Google for Astragalus arizonicus
Metadata
Record Modified: 2021-07-14Research By: Joseph A. Marcus