Astragalus purpusii M.E.Jones
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Authors
Rupert C. Barneby
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Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
"Sierra de Parras, Coahuila, Mexico, July 1910, 9,000 ft. alt. C. A. Purpus."’—Holotypus, Purpus 4582, POM! isotypi, BM, G, GH, P, US!
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Description
Species Description - Low or dwarf, caulescent perennial, with a stout woody taproot and branched, lignescent caudex shallowly buried in soil or litter, rather thinly strigulose with appressed or narrowly ascending hairs up to 0.35-0.7 mm. long, the herbage greenish or subcinereous, the leaflets glabrous above; stems diffuse, tufted or matted, the growth of the year 5-20 cm. long, simple or branched toward the base; stipules subherbaceous becoming papery-scarious, 1-5 mm. long, connate through ½-2/3 their length into a loose sheath; leaves 1.5-5 cm. long, shortly petioled or subsessile, with 13—23 crowded, oblong-obovate to oblanceolate, truncate-retuse, ciliate leaflets 1.5—6 mm. long; peduncles very slender, 1.5—4.5 cm. long; racemes closely 7-21-flowered, the flowers spreading and at length declined, the axis somewhat elongating, 0.4-1.6 cm. long in fruit; bracts membranous, pallid, lanceolate, 1.5—2.3 mm. long; pedicels at anthesis ± 0.6—0.8 mm. long, in fruit arched outward, a little thickened, 0.7-1.2 mm. long, tardily disjointing; bracteoles 0; calyx 2.4-3.6 mm. long, black-or fuscous-strigulose, the subsymmetric disc 0.4—0.5 mm. deep, the campanulate or obconic-campanulate tube 1.5-2.2 mm. long, 1.3-1.6 mm. in diameter, the slenderly or broadly subulate teeth 0.7-1.5 mm. long, the ventral pair commonly shortest, the whole becoming papery, marcescent, ruptured or not; petals pale purple, the banner striate; banner recurved through ± 45°, ovate-, obovate—, or suborbicular-cuneate, openly notched, 4.5 7.4 mm. long, 3.1-5 mm. wide; wings 4.1-5.7 mm. long, the claws 1.5-2 mm., the oblanceolate, narrowly oblong, or narrowly obovate, erose-emarginate or obtuse, slightly (and equally) incurved blades (2.8) 3-4.5 mm. long, 0.9-2 mm. wide; keel 3.5—4.3 mm. long, the claws 1.5-2 mm., the obliquely obovate or half- obovate blades 2—2.5 mm. long, 1.3—1.5 mm. wide, incurved through ± 80° to the blunt apex; anthers 0.25—0.3 mm. long; pod pendulous or declined, subsessile, obliquely ellipsoid or commonly widest above the middle and thus clavately ellipsoid, 5—8 mm. long, 2.2—3.4 mm. in diameter, cuneate or cuneately tapering at base, cuneate or abruptly contracted at apex into a conic cusp ± 1 mm. long, obtusely trigonous and a trifle laterally or dorsiventrally compressed, obtusely carinate ventrally by the convexly arched suture, flattened or shallowly sulcate dorsally, the thin, green, minutely strigulose valves becoming papery, stramineous, delicately cross-reticulate, inflexed as a complete or nearly complete septum 1.5-2.3 mm. wide; dehiscence unknown; ovules (2) 4-5; seeds (not seen ripe) ± 2-2.5 mm. long.
Distribution and Ecology - Alpine meadows and open ground in the pine belt, or with junipers and arbutus, 9000-12,150 feet, apparently rare, known only from the mountains of southern Coahuila (Sierra de Parras; northwest of Fraile) and adjoining Nuevo Leon (Cerro Potosi, municipio de Galeana).—Map No. 10.—June to September.
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Discussion
The Purpus milk-vetch recalls some mat-forming Ervoidei in general habit of growth and is easily recognized in Mexico by its low stature and tiny leaflets combined with very small, densely racemose flowers and obtusely trigonous, few-seeded, fully bilocular pod. In the first instance Jones referred A. Purpusi to the "Didymocarpus-Brazoensis group" and described the pod as stipitate and two-seeded. In reality the pod is usually 4-5-ovulate and often two fertile seeds develop in each locule of the fruit; moreover it is not distinctly stipitate but merely narrowly downward into a slenderly cuneate neck. Later Jones (1923, p. 281, Pl. 71) transferred the species to sect. Micranthi, a heterogeneous group of which all other members except A. micranthus and A. esperanzae are characterized by free stipules or deciduous fruits or both. It was placed next to A. Seatoni (our A. micranthus) in Atelophragma by Rydberg (l.c.) and can hardly belong elsewhere in the genus but in our equivalent sect. Strigulosi. It is peculiar in the section because of the very wide, complete or nearly complete septum, but the flower is closely similar to that of A. pueblae and A. micranthus, and the fruit on a small scale to that of A. cobrensis. The pod is bluntly trigonous but varies in compression, the cross-section being sometimes broader than high and at others higher than broad. In size and outline the pod resembles that of A. scalaris, and the flowers are similar in many details. However, the pod of A. scalaris is unilocular and the habit of growth and free stipules completely different.
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Objects
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Distribution
Coahuila Mexico North America| Nuevo León Mexico North America|