Monographs Details: Astragalus nuttallianus var. macilentus (Small) Barneby ex B.L.Turner
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

333c. Astragalus Nuttallianus var. macilentus

Variable in stature, robust or quite slender, strigulose-pilosulous with appressed, narrowly ascending, or incurved hairs up to 0.2-0.8 mm. long, the herbage green or cinereous, the leaflets glabrous or thinly pubescent above; stems mostly erect or ascending, rarely diffuse, 0.8-3 (3.8) dm. long; leaves (1.5) 2—9.5 cm. long, with 7—23 linear-elliptic, oblong-oblanceolate, broadly elliptic, or obovate leaflets 3—15 mm. long, these all acute, all obtuse, rarely all truncate-emarginate, or variably dimorphic, those of the upper leaves then narrowest; peduncles 2.5—9 cm. long; racemes loosely (2) 3—27-flowered, the axis nearly always somewhat elongating, (0.5) 1-3 cm. long in fruit; calyx 3.4-5.6 mm. long, thinly pubescent like the herbage with either black or white hairs, the tube 2-3.1 mm. long, 1.7—2.3 mm. in diameter, the subulate or linear-subulate teeth 1.1—3 mm. long; petals pale purple, or whitish with banner margined and keel tipped with lilac; banner (6.4) 8.5-13 mm. long, (4) 5-8.6 mm. wide; wings (6.1) 6.7-10.7 mm. long; keel (5) 5.4—9.3 mm. long, the claws 1.8—3.5 mm., the half-obovate blades (3.5) 3.7—7 mm. long, 1.8—3.2 mm. wide, abruptly incurved through 85—100° to the bluntly deltoid apex; pod ascending (commonly at a wide angle), spreading, or sometimes declined, contracted at base into a necklike stipe 0.3-0.9 mm. long, the body linear or linear-oblanceolate in profile, (1) 1.3-2.5 cm. long, 1.8—2.7 mm. in diameter, a little incurved at base and straight thereafter or gently incurved throughout, the green or purplish valves glabrous; ovules 12-22.—Collections: 28 (o); representative: L. B. Smith 33,358 (SMU, TEX); Cory 39,038 (TEX); Reverchon 1637 (NY, MO); Rose-Innes & Warnock 812 (SMU, TEX); Turner & Marshall 2510 (CAS, GH, RSA, TEX, US); G. L. Fisher 40,085 (CAS); Sperry (from Llano) in 1950 (ARIZ, CAS, WS).

Dry rocky hillsides, gravelly flats, and in disturbed soil along roads and railways, sometimes on gravel bars of summer-dry streams, apparently local but abundant locally in favorable years, especially in calcareous soils but not confined to them, southcentral Texas, from the Balcones Escarpment west across the Edwards Plateau nearly to the Pecos River, also in scattered stations west to El Paso.—Map No. 149.—March to May.

Astragalus Nuttallianus var. macilentus (Small) Barneby ap. B. L. Turner, Legum. Tex. 199. 1959, based on Hamosa macilenta (mean or meagre, descriptive of the typus) Small, Fl. S. E. U. S. 618, 1332. 1903.—"Type, along the Rio Blanco, Texas, Wright in herb C. U."— Holotypus, collected in 1850, NY! isotypus, GH!—Astragalus macilentus (Small) Cory in Rhodora 38: 406. 1936.

The var. macilentus as defined above is perplexingly polymorphic, the populations differing greatly one from another in number and shape of leaflets and in number and size of flowers. The nomenclaturally typical phase is apparently a rare thing. It is characterized by its short leaves composed of 3-5 pairs of leaflets, elliptic and acute or subacute in all leaves, and by racemes of about 3-7 comparatively small flowers, with banner 8.5-10 mm. long. Curiously enough the modern collections from trans-Pecos Texas match Wright’s typus better than do most specimens collected subsequently in eastern Texas. The common phase of var. macilentus on Edwards Plateau is a more leafy plant with up to 7-9 pairs of leaflets, these truncate-emarginate in all or most leaves; the flowers are essentially as in the preceding. About the east end of the variety's range, in a restricted area extending from Hays and Travis Counties northwest to Mason, McCulIoch, and Lampasas Counties, one encounters a robust form with some 7-11 pairs of leaflets varying in width and outline and either obtuse or subacute, combined with racemes of about 10-27 distinctly larger flowers, with banner 9.5—13 mm. and prominent keel 7-9.3 mm. long. Interestingly enough the increased length of the petals is not usually accompanied by a longer or larger calyx, and so the flowers are somewhat differently proportioned. This unusually handsome phase of the small-flowered milk-vetch appears quite distinct in its extreme form and during preliminary studies I annotated specimens as an unpublished variety; subsequently I have seen many intermediate states in flower-size and -number, and think it is better disposed of as a minor variant. I should add that the anthers of the large- flowered variant are substantially longer (mostly 0.45—0.6, not 0.3—0.45 mm.) than in the prevailing states of var. macilentus. Plants of extremely slender build, with exceptionally small flowers and short pods (described in parentheses above), represent the variety on granitic or metamorphic soils at Enchanted Rock in Llano County (Tharp in 1938; Rowell &. Barkley 17T286, both TEX); for the present they are likewise treated as a minor variant, but they will repay further study. They might be compared to the small-flowered states of A. leptocarpus.

The var. macilentus is the only Texan variety of A. Nuttallianus with blunt keel-tip. It almost always has much larger flowers than var. Nuttallianus and shorter pubescence, especially on the calyx, than the rather similar and partly sympatric var. pleianthus. The phase with large flowers is suggestive of the smallest-flowered forms of A. Lindheimeri as far as the individual flower is concerned, but the latter species is easily distinguished at anthesis by its short, few-flowered racemes and puberulent style, and later, of course, by the much broader, stoutly stipitate pod. When of average size the flower of var. macilentus closely resembles that of A. Emoryanus, of which the keel-tip is also bluntly deltoid; and when the leaflets are also all truncate-emarginate, the two species are difficult to tell apart until the fruit has formed. The pod of var. macilentus is contracted at base into a short stipe or stipelike neck and persists until dehiscence, that of A. Emoryanus is exactly sessile and deciduous when ripe. Rydberg’s records of Hamosa macilenta (1927, p. 327) from Mexico are based on specimens of A. Emoryanus, a species which he described but largely misunderstood. Jones’s reduction (1923, Index) of H. macilenta to A. leptocarpus could not have happened if he had examined the holotypus at NY.