Astragalus amphioxys A.Gray var. amphioxys
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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
"Southern Utah and New Mexico and Northern Arizona, Thurber, Parry, Palmer, etc...."—Lectotypus (Rydb., 1925, p. 148): Dona Ana, New Mexico, Thurber 295, GH!
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Synonyms
Astragalus shortianus var. minor A.Gray, Xylophacos amphioxys (A.Gray) Rydb., Astragalus amphioxys var. typicus Barneby, Astragalus crescenticarpus E.Sheld., Astragalus selenaeus Greene, Xylophacos aragalloides Rydb., , Xylophacos melanocalyx Rydb., Astragalus amphioxys var. melanocalyx (Rydb.) Tidestr., Astragalus marcusjonesii Munz
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Description
Variety Description - Calyx-tube (5.8) 7—10.5 mm. long, 3.2—4.2 (4.7) mm. in diameter, the teeth 3.7 (4.5) mm. long; banner (16.2) 19-24.5 mm. long, 8.2-12.2 mm. wide; wings (15.1) 18-22.4 mm. long, the claws (7.1) 8-11.5 mm., the blades (8.3) 9.5-11.5 mm. long, 2.4—4.2 mm. wide; keel (13.2) 14.3-18.8 (19.6) mm. long, the claws 6.5-11.8 mm., the blades 6.8-9.8 mm. long, 2.9-3.8 mm. wide; pod as described for the whole species; ovules (42) 44-56 (68), averaging ± 50.
Distribution and Ecology - Sandy valleys, plains, gravelly hillsides, sometimes on dunes, rarely on gumbo- clay flats, without apparent rock preference (except locally), 1600-6100 feet, widespread and locally plentiful from southern Nevada and southern Utah east across Arizona north of the Mogollon Escarpment into central New Mexico, south along the Rio Grande into extreme western Texas and adjoining Chihuahua. —Map No. 92.—Late March to June, and eastward again after summer or fall rains.
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Discussion
The var. amphioxys corresponds with var. typicus Barneby (1947, l.c.), modified by exclusion of some small-flowered plants now referred to var. modestus. The taxonomic history, synonymy, and morphological variation were discussed at length in the preliminary revision (1947, p. 438-440), and I comment here briefly on the polymorphic fruit and present a census of the more striking minor variants.
The pod of var. amphioxys varies from 1.5 to 5 cm. in length, although extremes outside a range of 2—4 cm. are uncommon. The absolute length appears to be the critical factor governing the degree of curvature, while this in turn largely determines the degree of dorsiventral compression at and near the middle. A long pod tends to become strongly incurved or coiled into a ring, is narrowly transverse-oblong in median section, and is laterally compressed at both ends. A pod of moderate size is ordinarily crescentic in profile, obcordate in median section, and shortly compressed at either end. The shortest type of pod tends to be little incurved, and the lateral compression of the basal segment may become obscure or obsolete. However, nearly straight pods of medium and great length are encountered occasionally. Generally speaking, the pod becomes thicker-textured, and hence more strongly rugulose on the lateral angles, toward the northwest edge of the species-range, especially north of the Grand Canyon. On the other hand, a brightly mottled pod, of sporadic occurrence throughout the range, is observed most frequently to the southeast.
The following minor variants deserve mention:
M. v. 1. Densely white-pubescent throughout; leaflets small, elliptic, subacute; pod relatively thin-walled, ± 5-7 mm. in diameter; range of the species, rare n. of the Colorado River (A. amphioxys, sens. str.).
M. v. 2. Robust; calyx commonly black-pubescent; leaflets averaging larger, variable in outline; pod more fleshy, becoming strongly rugulose on the angles, ±7-10 mm. in diameter; n.-w. Arizona and adjoining Utah and Nevada (Xylophacos melanocalyx; A. amphioxys X Layneae in part, as to material cited).
M. v. 3. Thinly strigulose, the herbage green; stems sometimes strongly developed; within the range of the last, an occasional shade form.
M. v. 4. Densely and finely silky-strigose throughout; leaflets narrowly elliptic, acute; calyx-teeth sometimes elongate; s.-w. Utah and s. Nevada, a dune ecotype (Xylophacos aragalloides).
M. v. 5. Strongly perennial, with woody root and caudex; foliage, calyx, and pod all very densely and shortly white-strigose; near Las Vegas, Nevada, a locally abundant ecotype of alkaline clay flats.
M. v. 6. Low, slender, often appearing annual; pod short, ± 1.5-2 cm. long, little incurved, cuneate rather than acuminate at base; n. Arizona, a vernal or starveling form sometimes associated with M. v. 1 (Xylophacos brachylobus sensu Rydb. as to the supposed typus, Palmer 102, in 1877, but excluding the basionym A. Shortianus var. brachylobus Gray = A. tephrodes var. brachylobus (Gray) Barneby, q. v. for fuller synonymy).
The range of A. amphioxys closely approaches the California state line, and the species is to be sought in the eastern Mohave Desert. However a specimen labeled "Mohave River District, s.-e. California" (Palmer 105 in 1876, NY ex herb. Canby.) needs confirmation.
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Objects
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Distribution
Nevada United States of America North America| Utah United States of America North America| Arizona United States of America North America| New Mexico United States of America North America| Texas United States of America North America| Chihuahua Mexico North America|