Monographs Details: Astragalus obcordatus Elliott
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:

303.  Astragalus obcordatus

Low, slender, diffuse, with a taproot and shortly forking caudex, glabrous except for a few scattered, subappressed and ascending hairs up to 0.3-0.5 mm. long on the leaf-stalks, the midrib of the leaflets beneath, and the inflorescence, the herbage green; stems several or numerous, prostrate or decumbent, 0.4-4 (5) dm. long, simple or spurred at 1-3 nodes preceding the first peduncle; stipules thinly herbaceous or the lowest papery, pallid or brownish, 2-4 (6) mm. long, ovate-triangular or lanceolate, ± semiamplexicaul-decurrent; leaves 5—12 (15) cm. long, slender-petioled, with (9) 15-27 rather distant and often scattered, oblong-obovate and retuse, cuneate-obcordate, or obcordate, flat leaflets 2-7 (10) mm. long; peduncles incurved-ascending, (1.5) 3-10 (12.5) cm. long, shorter than the leaf; racemes shortly but loosely 5-15 (18)-flowered, the flowers spreading or declined in age, the axis 1-4.5 (6) cm. long in fruit; bracts submembranous, often purple-margined, ovate, ovate-acuminate, or lanceolate, 1.2 2.5 (3.5) mm. long; pedicels at anthesis slender, ascending, 1-1.5 (1.8) mm. long, in fruit ascending or strongly arched outward, a trifle thickened, 1.5-2.8 mm. long, persistent or tardily disjointing; bracteoles 2, small, or 0; calyx 4.7-6.1 mm. long, thinly strigulose with white hairs, the subsymmetric disc 0.6-1 mm. deep, the submembranous, campanulate tube 2.7-3.5 mm. long, 2.2-2.8 mm. in diameter, the broadly subulate or lanceolate, herbaceous teeth (1.8) 2.2-2.8 mm. long, the whole becoming papery, marcescent usually unruptured; petals pinkish or bluish-lilac, the color early fading; banner recurved through 45-50° (or further in withering), obovate-, ovate-, or rhombic-cuneate, openly and shallowly notched, rarely subtruncate, 8.5-10.8 (11) mm. long, 4.5-6 mm. wide; wings 8-9.7 mm. long, the claws 3-3.4 mm., the obliquely oblanceolate or narrowly obovate, erose-undulate or obscurely emarginate, gently incurved or nearly straight blades 5.8-7.4 mm. long, 1.8-2.5 mm. wide; keel 6.5-8 mm. long, the claws 3-3.6 mm., the half-obovate blades 4-5.2 mm. long, (2) 2.2-2.7 mm. wide, abruptly incurved through 85-95° to the rounded apex; anthers 0.4-0.55 mm. long; pod ascending or loosely spreading (commonly humistrate), sessile on the conical receptacle or an incipient gynophore up to 0.6 mm. long, lunately half-ellipsoid or widest a trifle above the middle and nearly half-obovoid, (1.3) 1.6-2.5 (2.7) cm. long, (4) 4.5-7 (7.5) mm. in diameter, obconic or cuneately tapering at base, contracted distally into an erect or incurved cusp 0.3-2 mm. long, a little turgid but somewhat laterally compressed, carinate ventrally by the gently concave suture, shallowly and narrowly sulcate dorsally, the thinly fleshy, green or purple-tinged, glabrous valves becoming stiffly papery, stramineous or ultimately brownish, coarsely reticulate, inflexed at base of the pod as a rudimentary septum 0.2-0.6 mm. wide; dehiscence apical, tardy; ovules (13) 14-18 (19); seeds brown or soot-black, smooth or minutely pitted, dull, 1.6-2.5 mm. long.—Collections: 27 (o); representative: Curtiss 597 (ND, NY, SMU); Barnhart 1330, 2637 (NY); Small 11,399 (NY); Small & al. 11,268 (NY); G. V. Nash 307 (ND, NY).

Sandy pine woods of the Atlantic and Gulf Coastal Plains, apparently local, northern, western, and central peninsular Florida, south to Tampa Bay and Polk County, and probably in extreme southern Georgia; apparently isolated in southeastern Mississippi (near Pascagoula).—Map No. 138.—February to April.

Astragalus obcordatus (inversely heart-shaped, of the leaflets) Ell., Bot. S. C. & Ga. 2: 227. 1823.—"sent to me from St. Mary’s by the late Dr. Baldwin ... in the Southern Districts of Georgia, near St. Mary’s."—Spm. authent., labeled "838 Vicia? In flower March 14, 1813, south side of St. Mary’s River.," PH (herb. Muhlenberg.)! The corresponding entry in Muhlenberg’s Observationes indicates the collector as William Baldwin and the species as "new to Elliott."—A. Elliottii (Stephen Elliott, 1771-1830) D. Dietr., Syn. Pl. 4: 1080. 1847, a superfluous substitute, Dietrich having misread the epithet as odoratus, already used in the genus.—Tragacantha obcordata (Ell.) O. Kze., Rev. Gen. 946. 1891. Tium obcordatum (Ell.). Rydb. ap. Small, Fl. S. E. U. S. 1332. 1903. Batidophaca obcordata (Ell.) Rydb. in N. Amer. Fl. 24: 321. 1929.

The Florida milk-vetch, A. obcordatus, was placed by Jones (1923, p. 129, Pl. 26) and by Rydberg (1929, p. 321) in a section or genus so far apart from A. distortus that its close relationships, which were discerned by Gray (1864, p. 208), became altogether obscured. The species is similar to A. distortus and A. Soxmaniorum in habit of growth, and is most reliably distinguished by the prominently elevated reticulation of the mature fruit; it differs from the equally small-flowered A. distortus var. Engelmanni by its relatively long calyx-teeth and less strongly graduated petals.

Only one specimen of A. obcordatus collected outside of Florida is known to exist, Small & Wherry 11,726 (NY) from near Pascagoula, Mississippi; there is no record of the species from extreme western Florida or southern Alabama. If Baldwin’s original station was really to the south of St. Mary’s River as stated (in herb.) by Muhlenberg, the type-locality is in the present Duval County, Florida, where A. obcordatus has been collected several times in recent years, and not, as claimed, in the state of Georgia. The Florida milk-vetch approaches the Georgia State line in the Tallahassee region of western Florida and is to be sought north of the boundary in Grady and Decatur Counties.