Astragalus oocarpus A.Gray
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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(2): 597-1188.
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Family
Fabaceae
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Scientific Name
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Type
"Mountains east of San Diego, California, June (with flowers and ripe pods); Parry."—Holotypus, ("the original of Riocreux’s drawing"), collected in June, 1850, NY!
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Synonyms
Tragacantha oocarpa (A.Gray) Kuntze, Phaca oocarpa (A.Gray) Rydb.
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Description
Species Description - Tall, stout, amply leafy, with a woody taproot and superficial root-crown, appearing glabrous below the inflorescence, the stems truly so, the margins and midribs of the leaflets thinly strigulose with appressed or narrowly ascending hairs up to 0.3—0.5 mm long, the herbage deep green and of firm texture; stems stiffly erect and ascending, or finally straggling and supported on bushes, 6—13 dm. long, simple, fistular, striate below, branched or spurred at 2—6 nodes preceding the first peduncle, floriferous in the upper third or fourth; stipules herbaceous becoming papery, fragile, the lower ones commonly deciduous in age, 2—14 mm. long, triangular-acuminate from a broad, decurrent base, about semiamplexicaul, deflexed; leaves (4.5) 6-17 cm. long, shortly petioled or the upper ones sub- sessile, with stout, grooved rachis and (17) 19-35 broadly lanceolate to oblong- ovate or -obovate, retuse or truncate-obtuse (and then often apiculate), flat, penninerved, dorsally carinate leaflets 6-33 mm. long; peduncles stout, erect or incurved-ascending, 1.5-6 (7) cm. long, much shorter than the leaf; racemes loosely, or in early anthesis subcompactly (15) 20-60 (75)-flowered, the flowers ascending at a wide angle, the axis (3) 4-19 cm. long in fruit; bracts triangular- lanceolate, 1.2-3 mm. long; pedicels ascending, straight, at anthesis 1-1.4 mm., in fruit greatly thickened, 2-3.5 mm. long, persistent; bracteoles 0-2; calyx 4.5-6 mm. long, thinly strigulose with white hairs but the sinuses of the teeth often densely and canescently ciliate, the subsymmetric disc 1-1.5 mm. deep, the campanulate tube 3.5-4.6 mm. long, 2.9-3.8 mm. in diameter, the deltoid or subulate teeth 0.8-1.8 mm. long, the whole becoming papery, ruptured, fragile but marcescent; petals ochroleucous (reportedly sometimes purple-tinged), little graduated, somewhat fleshy and commonly drying brown; banner abruptly recurved through 70-90°, broadly rhombic-, ovate-, or obovate-flabellate, shallowly notched, 10.5—12.5 mm. long, 7.5-9 mm. wide; wings 10.1-11.6 mm. long, the claws 3.6-4 mm., the oblanceolate, obliquely obovate or half-obovate, obtuse, straight or gently incurved blades 7.7-8.2 mm. long, 2.8-3.8 mm. wide; keel 9-10.8 mm. long, the claws 3.7-4.4 mm., the lunately half-elliptic blades 5.6-7.2 mm. long, 2.8-3.3 mm. wide, abruptly incurved through 85-95° to the sharply triangular apex; anthers (0.55) 0.6-0.8 mm. long; pod erect, persistent on the receptacle, sessile but contracted at base into a thick, broadly obconic neck, obliquely ovoid- acuminate, contracted distally into a triangular-acuminate, laterally flattened, erect or slightly incurved beak 4-7 mm. long, greatly inflated but scarcely bladdery, 2.5 cm. long, (8.5) 10-16 mm. in diameter, terete or a trifle dorsiventrally compressed, shallowly sulcate ventrally, the thinly fleshy, green, glabrous or minutely strigulose valves becoming stiffly papery, stramineous, not inflexed, the funicular flange 1-1.7 mm. wide; dehiscence apical, through the slightly gaping beak; ovules 44-58; seeds brown, pitted or rugulose or both, dull, 3-3.2 mm. long.
Distribution and Ecology - Openings in chaparral and on gravelly flats and slopes in thin oak woodland, (1500) 2700-5000 feet, local but forming colonies, cismontane slope of the mountains of interior San Diego County, California (Palomar Mountain to Mesa Grande, Julian, and Descanso).—Map No. 113.—May to August.
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Discussion
The egg-pod milk-vetch, A. oocarpus, is a coarse, ungainly astragalus, with stout, striate, hollow-cored stems, ample leaves composed of many (about 21-35) leathery, visibly nerved leaflets, and racemes of numerous, small, dingily ochroleucous flowers followed by erect, inflated but stiff-walled fruits. It is assumed to have arisen by mutation from A. Douglasii var. Parishii of which it has retained most precisely the size, shape, and color of the petals together with a calyx similarly proportioned and bearing around the sinuses between the teeth a band of silvery hairs which contrasts with a glabrescent tube. It differs in essence from A. Douglasii by a thickening and coarsening of all its tissues, an effect particularly noticeable in the petals, which are of decidedly fleshy texture and turn brown in the press unless dried with more than usual care and dispatch. The pod, which is not significantly different from that of A. Douglasii in structure, has also assumed a texture abnormally thick for the section; at the same time the joint between it and the receptacle has been suppressed, so that it remains firmly attached to the greatly thickened pedicels until dehiscence and afterward. This acquisition of an emmenoloboid pod seems surely to denote a reversal of the ordinary evolutionary sequence in the genus. The species differs further from var. Parishii, which is of fairly frequent occurrence in the higher parts of interior San Diego County, in its erect stems becoming diffuse only late in the season, if ever, when they have reached a length of three or four feet. The related A. Douglasii var. perstrictus, which is confined to a small area in the southeast corner of the county, resembles A. oocarpus in stature and is only distinguishable, before the papery pod has formed, by the less numerous (13-19) leaflets thinly pubescent on both sides. Usually A. oocarpus flowers later in the year than other astragali of the region and continues to bear flowers and fruits into the height of summer. A third milk-vetch with rather small, ochroleucous flowers must be carefully distinguished. This is A. Deanei, endemic to southwestern San Diego County but at elevations well below those favored by A. oocarpus, which it resembles in its numerous (21-29) green and almost hairless leaflets. It may be recognized by the graduated petals with banner longer and keel shorter than in A. oocarpus, the longer calyx-teeth, and, like A. Douglasii, by its deciduous pod with ripe valves of papery texture.
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Objects
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Distribution
California United States of America North America|