Monographs Details: Astragalus leptocarpus Torr. & A.Gray
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:

334.  Astragalus leptocarpus

Precocious annual, with a slender taproot, variable in stature but commonly low and delicate, the stems, leaf-rachises, and peduncles thinly (or when young somewhat densely) strigulose with straight, appressed or subappressed hairs up to 0.3—0.5 mm. long, the leaflets green and glabrous except for a few hairs along the margins and the midrib beneath; stems solitary and erect or 2-8 from the root- crown and then ascending, decumbent, or (especially in hard soils) prostrate and radiating, (1.5) 3-20 (30) cm. long, simple except in the most robust plants, often purplish at base; stipules submembranous, pale green or purplish, (1) 1.5-5 mm. long, the short lowest ones becoming pallid and fragile in age, the median and upper ones narrowly triangular or lance-acuminate, all about semiamplexicaul, glabrous dorsally, the margins ciliate and commonly beset with a few knob- or tack-shaped processes; leaves 1.5-6 (7) cm. long, the lowest shortly petioled, the rest subsessile, with (7) 11-17 (19) oblong-, obovate-, or oblanceolate-cuneate, retuse or emarginate, or in some lower leaves broadly cuneate- obcordate, flat, rather thick-textured leaflets 2-10 (12) mm. long; peduncles erect from erect-ascending and divaricate from procumbent stems, (2) 2.5-9 (10) cm. long, all but some early ones surpassing the leaf; racemes loosely but very shortly (1) 2-7 (12)-flowered, the flowers spreading or widely ascending, the axis not or scarcely elongating, 0-12 (20) mm. long in fruit; bracts membranous, pallid or purplish, ovate or lanceolate, 0.8-2 mm. long; pedicels ascending or a little arched outward in age, at anthesis 0.4-1.1 mm., in fruit somewhat thickened and 0.8-1.7 mm. long, persistent; bracteoles 0; calyx (3) 3.6-4.5 (5.3) mm. long, strigulose with white or rarely with some or all fuscous or black hairs up to 0.25-0.4 mm. long, the subsymmetric disc 0.5-0.8 mm. deep, the campanulate tube (1.8) 2—2.4 (2.8) mm. long, (1.4) 1.6—2.2 (2.7) mm. in diameter, the rather broadly subulate teeth 1.2—2.2 (2.8) mm. long, the whole becoming papery, marcescent unruptured; petals magenta- or amethystine-purple, drying violet, the banner with a large, white, striate eye, the wings often white-spotted distally near the inner margin; banner gently recurved through ± 40°, ovate-cuneate or broadly rhombic-elliptic, deeply notched, (5.2) 8.3-12 (13.2) mm. long, (4) 5.2-7.4 (8.4) mm. wide; wings (5) 7.2-9.8 (11.3) mm. long, the claws (1) 2-2.5 (2.9) mm., the oblanceolate or narrowly oblong-elliptic, obtuse but often erose-undulate, slightly incurved blades (5) 5.7-7.5 (8.8) mm. long, 1.4-3 (3.3) mm. wide; keel (4.5) 6-7.8 (9) mm. long, the claws (1.2) 2.1-2.8 (3.1) mm., the half-elliptic or obliquely triangular blades (3.4) 3.9-5 (6) mm. long, (1.7) 2—2.4 (2.7) mm. wide, abruptly incurved through 85-95° to the narrowly triangular, acute, porrect, often beaklike apex; anthers 0.35-0.45 (0.5) mm. long; pod horizontally spreading or ascending at a wide angle, sessile but cuneately tapering at base into a thick, sometimes stipelike neck up to 0.5 mm. long, narrowly linear or linear-oblanceolate in profile, straight or rarely slightly and evenly incurved, narrowly cuneate and shortly cuspidate at apex, (1.7) 2—3.7 cm. long, 2.2—3.1 (3.5) mm. in diameter, triquetrously compressed with at first nearly flat but ultimately convex lateral and narrower, narrowly sulcate dorsal faces, carinate ventrally by the rather thick, prominent suture, the very slightly fleshy, green or purplish, glabrous valves becoming papery, at first brownish but ultimately almost black, delicately cross-reticulate, inflexed as a complete septum about 1.5—1.8 mm. wide; dehiscence apical and downward through the ventral suture, the septum also splitting in age, and the valves somewhat coiled distally; ovules (17) 20—26; seeds subquadrate, pale brown sometimes speckled with purple, smooth but scarcely lustrous, 1.7-2.2 mm. long.—Collections: 70 (i); representative: Tracy 9104 (NY, SMU, TEX, WIS), 9111 (NY, TEX); Shinners 9807, 9920 (OKLA, SMU), 11,030 (SMU, TEX); Cory 55,397 (SMU, WS); Reverchon 241 (NY, SMU); F. H. Wagner 21 (NY, SMU).

Open post oak woodlands, mesquite thickets, sandy fallow fields and roadsides, mostly in light porous soils, 5-1000 feet, locally plentiful on the Gulf Coastal Plain in eastern Texas, from the mouth of the Rio Grande to the lower Neches River and the Balcones Escarpment, north, becoming less frequent, on calcareous prairies to Dallas and Eastland Counties; one old record from "Arkansas" requires confirmation.—Map No. 151.—March to May.

Astragalus leptocarpus (with slender pod) T. & G., Fl. N. Amer. 1: 334. 1838.—"Near the Sabine River, Dr. Leavenworth! Texas, Drummond!""—Cotypi, labeled: "Arkansas, Leavenworth," and ‘Texas, Drummond Coll. I," NY! isotypi (Drummond), BM, G, GH, OXF, P!— Tragacantha leptocarpa (T. & G.) O. Kze., Rev. Gen. 946. 1891. Hamosa leptocarpa (T. & G.) Rydb. ap. Small, Fl. SE. U. S. 617, 1332. 1903.

Astragalus Nuttallianus var. leptocarpoides (resembling A. leptocarpus) Jones, Contrib. West. Bot. 8: 22. 1898.—"Galveston Is., Texas, on dry prairies, May 1, 1843, Lindheimer, Mo. Bot. Gard. Nos. 17070, 17071."—Holotypus (2 sheets), MO! istoypus, GH!—Hamosa leptocarpoides (Jones) Rydb. in Bull. Torr. Club 54: 326. 1927. Astragalus leptocarpoides (Jones) Cory in Rhodora 38: 406. 1936.

The bodkin milk-vetch, A. leptocarpus, is a pretty little species with small, brightly colored flowers, sometimes faintly, yet agreeably fragrant It is closely related to A. Nuttallianus and might logically be treated as forming part of that polymorphic complex; for apart from the ordinarily longer pod enclosing from one to four extra pairs of ovules and seeds, it possesses no single attribute which cannot be matched somewhere in A. Nuttallianus. In practice it is easily distinguished from sympatric varieties of A. Nuttallianus: from var. trichocarpus by its glabrous ovary; from var. pleianthus by its retuse leaflets; from var. macilentus by the acute keel-tip; and from var. Nuttallianus, which it most nearly resembles in its green, glabrescent foliage and in shape of the leaflets, by the nearly always longer and more amply proportioned flower. However a rare form occurs, sometimes associated with normal plants, in which the flowers are quite small, with calyx scarcely over 3 mm. and banner 5.2-6 mm. long (and other petals proportionately shortened), as noted in parentheses in the description. Individual specimens of this sort might be confused with var. Nuttallianus but still differ in their shorter calyx-teeth, in ovule-number, and ultimately in the long, commonly straight pod. Like occasional "gigas" individuals with abnormally large flowers, they are interpreted as sporadic and taxonomically unimportant variants. In other respects A. leptocarpus varies little. The pod is traditionally described as straight, but is quite often slightly and evenly arched through the whole length (but not more abruptly so at base than distally), and the stems vary from erect to prostrate, as do those of most annual astragali. The typus of var. leptocarpoides is only unusual in so far as a curved pod and prostrate stems are combined in the same plant with relatively small flowers. It has the 20-22 ovules of A. leptocarpus. The species was collected first by Berlandier (No. 1431, G), between Bexar and Austin, in 1832.