Astragalus plattensis

Low, diffuse or decumbent, with an oblique or vertical, often deeply buried (and seldom collected) woody taproot giving rise to slender, branched and often widely creeping, subterranean caudex-branches, these often furnished at the nodes with adventitious rootlets, the stems emerging from the soil singly or few together to form loosely entangled mats or more widely spaced and apparently independent growths, the whole plant (or at least the stems, petioles, peduncles, or some of these) thinly to densely pilose with widely to narrowly ascending or spreading, rarely subappressed, straight or subsinuous, lustrous hairs up to (0.9) 1-1.5 (1.9) mm. long, these often mixed with shorter, curly ones, the herbage green or grayish- green, the leaflets usually less densely pubescent to medially glabrescent or often quite glabrous above; stems of the year (excluding the similar but indurated caudex-branches) for a space of 1-20 cm. slender, simple, subterranean, becoming on emergence stouter and bearing 1-several spurs or divaricate branches at the early aerial nodes, simple distally, the main axis above ground (0.5) 1-2.5 (3.7) dm. long; stipules dimorphic and variable, 1.5-7 mm. long, those at the lowest leafless nodes the smallest, papery or scarious, either semiamplexicaul or fully so and connate into a bidentate or truncate sheath, the median and upper ones herbaceous, glabrous or glabrescent dorsally, the median commonly broadly ovate- or asymmetrically obcordate-acuminate and broader than the stem, the upper ones narrower, rarely all narrow and lanceolate, embracing half to the whole stem’s circumference, the margins either in contact but free, or connate for a short space, the blades ciliate and the margins also bearing a few minute, knob- or tack-shaped processes; leaves 2.5—11.5 cm. long, shortly petioled or the uppermost subsessile, with (11) 15—27 broadly to narrowly elliptic, oval, or oblong, obtuse or acute, or in some lower or rarely all leaves oblong-obovate and truncate- emarginate, flat or loosely folded leaflets (2) 4-13 (17) mm. long; peduncles ascending, or divaricately humistrate in fruit, (1) 2-7.5 cm. long, shorter than the leaf; racemes loosely but shortly, at first often subumbellately (3) 6—15-flowered, the flowers ascending or spreading, the axis little elongating, 0.7-2.5 (3.2) cm. long in fruit; bracts submembranous, pallid, greenish, or purplish, lanceolate or ovate-acuminate, (2) 3—7.5 mm. long; pedicels at anthesis ascending, straight, 1.4-2.8 mm. long, in fruit thickened, sometimes a little arched outward, 2.4—3.8 mm. long; bracteoles commonly 2, sometimes rudimentary or 0; calyx 7.8—12.2 (13.7) mm. long, pilose like the herbage or more shortly pilosulous with white or sometimes largely black hairs, the oblique disc 1.1—2 mm. deep, the rather deeply campanulate, basally oblique (or when broad a trifle gibbous), membranous, purplish tube 5.4—7.8 mm. long, 3.2—5 (5.3) mm. in diameter, the subulate or lance-subulate, herbaceous teeth (2) 2.6—4.7 (6.1) mm. long, the whole becoming papery-scarious, ruptured, marcescent; petals pink- or lilac- purple, the color fugacious in drying, the banner sometimes largely pallid, but keel and wings at least purple-tipped; banner broadly oblanceolate, oblong- or ovate-cuneate, usually deeply notched, (14.3) 16.5—20 (21.5) mm. long, 6.5—10.2 mm. wide; wings (13) 14.5—17 (18.4) mm. long, the claws (5.9) 6.3—8.2 (9) mm., the oblong-oblanceolate or -elliptic, nearly straight blades 8—10.8 mm. long, (2.3) 2.7-3.7 mm. wide, nearly always obliquely notched or undulate-truncate dorsally below the obtuse apex, rarely obtuse and entire; keel (11.5) 12—15.5 (16) mm. long, the claws (6) 6.4-8.7 mm., the lunately elliptic blades (6.1) 6.5-8.1 mm. long, (2.8) 3-3.9 mm. wide, rather gently incurved through 80-95 to the blunt apex; anthers 0.5-0.7 (0.75) mm. long; pod ascending or spreading (humistrate), sessile, long persisting on but finally disjointing from the receptacle (this sometimes produced as a thick, glabrous, stipelike neck up to 1.3 mm. long), the body obliquely ovoid-oblong, or subglobose, 1-1.7 cm. long, 1-1.3 cm. in diameter, truncate or shallowly cordate at base, abruptly contracted distally into a narrowly conic-subulate, rigid beak 1—3.5 mm. long, a trifle obcompressed, sulcate both dorsally and ventrally, the sutures both thick but embedded in the valves and not salient, the ventral suture nearly straight or at least much less strongly convex than the dorsal one, the thick, fleshy, green but often purplecheeked or -mottled valves strigulose or pilosulous with appressed or narrowly ascending hairs up to 0.45-0.8 mm. long, becoming brown, stiffly leathery, transversely rugulose and 0.9-1.3 mm. thick at maturity, inflexed as a complete septum 3.6-6 mm. wide; dehiscence tardy, through the beak and ultimately through both sutures and the septum, the halves finally falling apart; ovules (28) 32-48 (52); seeds pinkish-brown turning purplish- or soot-black, smooth but dull, 2.5-3.3 (3.6) mm. long.—Collections: 141 (v); representative: C. L. Porter 3547 (NY, RM, SMU, TEX); Rydberg 615 (NY); Cory 56,269 (OKLA, SMU, WS); Ripley & Barneby 7506 (CAS, RSA, UTC); Cory 54,050 (OKLA, SMU, WS); D. Denton (from Ivan, Texas) in 1931 (NY, SMU, TEX, WS); Tolstead 6902 (MO, SMU).

Plains and low rolling hills, commonly on clay-loam or sandy clay prairies, also in abandoned pasture, fallow fields, and gravelly gullies and openings in oak woodland, (100) 500-4550 feet, now most common along fenced rights-of-way, widespread and common southward, becoming rarer northward, Edwards Plateau, southcentral Texas (one old record from the Gulf Coastal Plain near Matagorda Bay) north to eastern Colorado, northeastern Wyoming, and the Souris River in northcentral North Dakota, east to the James River in South Dakota, eastern Nebraska, and the lower Republican River in eastern Kansas; reported (Fernald, 1950, p. 912) from Minnesota, Illinois, and Alabama, the records from the last two states based on A. tennessensis.—Map No. 102.—Late March (southward) to mid-July.

Astragalus plattensis (of the Platte River) Nutt. ex T. & G., Fl. N. Amer. 1: 332. 1838 ("Plattensis?’).—"Plains of the Platte, Nuttall! Dr. James!""""—Holotypus, labeled by Nuttall "Astragalus *plattensis. Platte Plains," BM! isotypi, GH, NY, PH!—Tragacantha plattensis (Nutt.) O. Kze., Rev. Gen. 947. 1891. Phaca plattensis (Nutt.) MacM., Metasp. Minn. Vail. 325. 1892, in syn. Geoprumnon plattense (Nutt.) Rydb. ap. Small, Fl. S.E. U. S. 1332. 1903.

Astragalus pachycarpus (with thick-textured pod) T. & G., Fl. N. Amer. 1: 332. 1838.— "Prairies of Arkansas, Dr. Leavenworth!"—Holotypus, consisting of 3 ripe, fallen pods, labeled by Torrey "the original specimens," NY! isotypus, K!—A. crassicarpus var. pachycarpus (T. & G.) Jones, Contrib. West. Bot. 8: 16. 1898. Geoprumnon pachycarpum (T. & G.) Rydb. ap. Small, Fl. S.E. U. S. 1332. 1903.

The range of the Platte River milk-vetch lies within that of its commoner relative A. crassicarpus, and the two species have often been confused. However, with exceptions so rare as to be negligible in practice, the ovary and pod of the common ground-plum are glabrous, whereas those of A. plattensis are consistently pubescent. Everywhere, except in southcentral Texas, the growing plants of A. plattensis are easily distinguished by their habit alone, for the stems emerge singly or few together from subterranean caudex-branches more slender than the aerial parts. The stems of typical A. crassicarpus arise together in clumps from the knotty root- crown at or barely below the level of the soil and are not noticeably more slender at base than distally. In parts of southcentral Texas A. plattensis and A. crassicarpus var. Berlandieri are sympatric, and they are so much alike in habit of growth that flowering specimens are best determined by search for hairs on the ovary. The fully formed fruit of the Platte River milk-vetch, even when detached from the parent plant, is by itself diagnostic of the species. Fleshy and thick-walled as in the other ground-plums, it is distinguished by being grooved along both sutures, commonly more deeply so ventrally than dorsally, so that it resembles that of some inflated Oxytropis externally, however different in inward structure.

The stipules of A. plattensis are astonishingly variable in form and attachment. Plants with stipules at the buried nodes connate into a small, bell-shaped sheath and upper ones amplexicaul and united at base are forcibly reminiscent of some large-flowered Scytocarpi, being altogether similar in organization and gross aspect up to the eventually (even though tardily) deciduous and fully bilocular, thick-walled pod. On the other hand, the free-stipuled plants, apparently by far the commoner sort, closely resemble A. crassicarpus var. Berlandieri except in the usually more copious and longer pubescence of the leaves and the grooved pubescent fruit.

The wide distribution east of the Mississippi attributed to A. plattensis by Rydberg and Fernald has not been confirmed by specimens. It is based largely on misunderstood records of A. tennesseensis, formerly treated as a variety of the Platte River milk-vetch. The species is excluded from the flora of Illinois by Jones & Fuller (Vasc. Pl. I11. 273. 1956).

The holotypus of A. pachycarpus, of which the controversial history has been told elsewhere (Barneby, 1956, p. 500), consists of three ripe pods, remarkable only because they are now hairless, probably glabrate through weathering on the ground. The leafy fragments associated with these fruits are not surely relevant; and if they were so, they would be inconclusive The fruits are wholly characteristic of the Platte River milk-vetch and cannot be referred to any known species with normally glabrous pod. Dr. Leavenworth’s Arkansas was a vague term, including parts of the present Oklahoma, where A. plattensis is still one of the commoner astragali. Rydberg’s Geoprumnon pachycarpum (1926, p. 164) is our A. crassicarpus var. Berlandieri with a small element of var. cavus.