Monographs Details: Astragalus lentiginosus var. ambiguus Barneby
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Description:Latin Diagnosis - var. vitreo proxima, imprimis legumine subcoriaceo nec chartaceo diversa.
Variety Description - Coarse perennial, the stout, erect stems stramineous, the herbage thinly strigulose or nearly glabrous, the leaflets bicolored, yellow-green and glabrous above, stems 3—5 dm. long, spurred below, floriferous from near or below the middle; leaves 7—14 cm. long, with 13—21 oblong-obovate or oblanceolate, retuse- emarginate, flat leaflets (3) 7.5—15 mm. long; peduncles erect, 7—11 cm. long; racemes loosely (7) 15—20-flowered, the axis (4) 5.5—9 cm. long in fruit; calyx 6.7-8 mm. long, thinly white or black-strigulose, the tube 5-5.7 mm., the teeth 1.6—2.3 mm. long; petals purple, drying violet, the auricles of the wings often fleshy-thickened; banner (13) 15—16.7 mm. long; wings 11—14 mm. long, the claws 5.1-6 mm., the blades 6.5-8.8 mm. long; keel 11.3-12.2 mm. long, the claws 5.6—5.8 mm., the blades 6.1—7.3 mm. long; pod 1.5—2.2 cm. long, inflated but firm, ± 9—13 mm. in diameter, the body plumply ovoid or subglobose, the beak 2-5 mm. long, broadly deltoid to triangular-acuminate, the valves stiffly papery or almost leathery, glabrous or rarely puberulent, green becoming stramineous and lustrous, not mottled; ovules 22—34.
Distribution and Ecology - Open hillsides, 4000-4800 feet, on limestone or granite, local but forming colonies, known only from Mohave County, Arizona, south of the Colorado River.—Map No. 131.—April and May.
Discussion:The freckled milk-vetch described here as var. ambiguus has been known for many years, but no satisfactory disposition of the material has ever been made. Jones labeled his collection from Chloride as "var. yuccanus varying toward var. mokiacensis," and I was probably influenced by this annotation when I interpreted the plant as a form of var. mokiacensis with inflated fruit. The genuine A. mokiacensis, although quite like var. ambiguus in habit and in details of the flower, is an emmenoloboid species transferred in these pages to sect. Preussiani; consequently the Peach Springs astragalus (or fma. (3), a genuine member of the A. lentiginosus complex, has been left without name or niche in the genus. It is apparently most nearly related to var. vitreus and var. diphysus, resembling the former in habit but differing in the leathery pod and separable from the latter by the open racemes which reach a length of 5-9 cm. in fruit. Even in the small amount of material available, which may represent samples from only two populations, there is some perceptible but hardly significant variation in pubescence and flower-size. At Peach Springs the ovary and pod are glabrous, but in the plant from Chloride thinly strigulose.
Arizona United States of America North America