Astragalus lancearius 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(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
"Near Beaverdam on the Rio Virgen, northwest corner of Arizona, Dr. Palmer, 1877."—Holotypus, Palmer 114 in 1877, GH! isotypi, K, NY!
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Synonyms
Homalobus lancearius (A.Gray) Rydb.
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Description
Species Description - Wiry, sparsely leafy or almost leafless, closely resembling A. Episcopus in habit of growth, strigulose with filiform or somewhat flattened hairs up to 0.35-0.5 mm. long, the stems greenish, the growing tips cinereous, the leaflets (when present) equally pubescent on both sides; stems few or solitary, 2-4.5 dm. long, erect or incurved-ascending, simple and subterranean for a space of 2.5-10 cm., stouter and purplish on emergence, divaricately branched up to the first peduncle, the branches either solitary or disposed in unequal pairs, or (upward) paired with a sterile spur or a peduncle, the more robust branches commonly again branched, the internodes flexuous or zigzag; stipules dimorphic, the papery lower ones up to 3-6 mm. long, adnate to the suppressed petiole, semi- or almost fully amplexicaul but free, the upper ones shorter, narrower, herbaceous, with deltoid-acuminate or triangular, erect or deflexed blades; leaves (2) 4-9.5 cm. long, most of them, sometimes all, the uppermost always, reduced to a naked rachis often a trifle expanded and hooked at apex, a few of them (usually the lowest) bearing 1-3 pairs of distant, opposite or scattered, firmly petiolulate, linear or linear-elliptic, obtuse or subacute, involute leaflets 2-14 mm. long; peduncles 4-17 cm. long, the lower ones stout, the upper slender or subfiliform, all surpassing the leaf; racemes loosely or remotely (6) 10-25-flowered, the axis elongating, (3) 5-26 cm. long in fruit; bracts thinly herbaceous becoming papery, ovate-triangular, 1-1.5 mm. long; pedicels at anthesis straight, ascending 1-2 mm. long, in fruit recurved or refracted, somewhat thickened, up to 3 mm. long; bracteoles minute or 0; calyx 3.8—4.8 mm. long, strigulose with white or mixed black and white hairs, the campanulate tube 3-3.5 mm. long, 2.2-2.6 in diameter, the deltoid or broadly triangular-subulate teeth 0.7-1.3 mm. long, the whole becoming papery, ruptured, marcescent; petals whitish or faintly pink- or lilac-tinged; banner recurved through ± 45°, rhombic- elliptic, notched, 9.5-11.5 mm. long, 5.5-6 mm. wide; wings 9.3-10.2 mm. long, the claws 3.6—4.5 mm., the narrowly oblanceolate, obtuse, scarcely incurved blades 5.9—6.4 mm. long, ±2 mm. wide; keel 7.7—8.4 mm. long, the claws 3.5 4.5 mm., the half-obovate blades 4.2-4.8 mm. long, 2.1-2.6 mm. wide, incurved through 90-95° to the obtuse apex; anthers 0.5-0.65 mm. long; pod deflexed, sessile or almost so, narrowly or sometimes broadly lanceolate to lance-oblong or linear-elliptic in profile, either nearly straight and subsymmetrically cuneate or cuneate-acuminate at both ends, or gently arched downward and the dorsal suture then straight to slightly concave and the ventral one strongly convex, the whole 2-3.4 cm. long, 5—7 (9) mm. in diameter, very strongly compressed, with nearly flat sides and salient sutures, the thin, pale green, glabrous or strigulose valves becoming stramineous, papery, lustrous, delicately reticulate, not inflexed; ovules 8-14; seeds (little known) brown, sometimes purple-dotted, pitted but ± lustrous, 3.5-3.8 mm. long.
Distribution and Ecology - Sandy clay flats and barren gravelly knolls and hillsides, on sandstone (and perhaps on limestone), 2000—5500 feet, rare and local, known only from the Virgin Valley in Washington County, Utah, and the Beaver Dam Mountains in adjoining Arizona, east to the canyon of the Paria in Kane County, Utah, and the north foothills of the Kaibab south of Kanab.—Map No. 24.—April to June.
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Discussion
The lancer milk-vetch, A. lancearius, is closely related to and presumably derived from the much commoner and better known A. Episcopus, and it could reasonably be reduced to varietal rank. The two species are virtually identical in habit of growth, and their pods are essentially alike in exterior form and structure. Nevertheless A. lancearius is easily distinguished by its shorter, differently proportioned calyx, and this alteration in the flower accompanied by an abrupt diminution in ovule-number from 8-13 to 4-7 pairs justifies its recognition as a species, at least pending discovery of intermediate forms. The pod of A. lancearius is of slightly thinner texture than that of A. Episcopus so that the reticulation of the ripe valves is elevated and conspicuous rather than largely or almost wholly immersed.
The species, poorly understood in the past, is still known from too few collections. Rydberg (1929, p. 257) thought it differed from A. Episcopus in its truly sessile rather than shortly stipitate pod, but this character no longer serves to divide the material into credible species. Jones (1923, p. 67) attributed to A. lancearius peduncles longer than the leaves and relatively long, subulate calyx-teeth in contrast to short peduncles and short, blunt teeth in A. Episcopus. The peduncles surpass the leaves in both species, and annotations (POM) show that Jones had transferred his concept of A. lancearius from the original plant of the Beaver Dam Mountains to one which he collected in quantity in the San Rafael Swell during the summer of 1915. The latter is our A. Episcopus, and it is clear that Jones had lost sight of the genuine and much rarer A. lancearius, of which he possessed very little material. Encountering the problem several years ago, (1947, p. 32) I naively misinterpreted the differences in the flowers of A. lancearius and A. Episcopus as examples of random variation and overlooked the important ovule-character. I was not only misled by Jones but also influenced by having collected typical A. lancearius near Kanab, Utah, which I believed to be the type-locality (although this is quite uncertain) of A. Episcopus. It seemed improbable in the extreme that two species so much alike could grow together. I now know, however, that genuine A. Episcopus does extend west as far as Pipe Springs in the valley of Kanab Creek, whereas A. lancearius has been traced east along the Zion Escarpment as far as the Paria Canyon in Utah and the Buckskin Mountains (Jones’s term for the north foothills of the Kaibab) in Arizona. The ranges of the two species apparently overlap slightly but there is yet no sign of intergradient populations.
The few collections of A. lancearius now available for study suggest that racial differentiation is still active in the species. In the Virgin Valley the pod is glabrous and symmetrically lanceolate, with both sutures equally convex. East of Zion the almost always strigulose pod varies in profile from straight and subsymmetric to definitely decurved and thus strongly asymmetric in profile, with straight or even slightly concave dorsal and strongly bowed ventral sutures. In the related A. Episcopus the pod is known to vary from glabrous to strigulose within the limits of a small and obviously monophyletic population.
The epithet lancearius was misspelled "lancelarius" in Rydberg’s Flora of the Rocky Mountains, and the incorrect version has attained a spurious vitality by use in herbaria.
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Distribution
Arizona United States of America North America| Utah United States of America North America|