Astragalus humistratus 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
"Pebbly bed of a stream and on hills under pine-trees, near the copper mines, New Mexico; Aug. (1003)."—Holotypus (Wright 1003), collected in 1851, GH! isotypi, BM, K, NY, PH, US!
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Description
Species Description - Prostrate, diffuse, or weakly assurgent, sometimes matted, the several or many stems radiating from the root-crown or caudex, slender and wiry or rather coarse, (0.4) 1.7-6 (8) dm. long, freely branched below the middle, more shortly branched or spurred at most nodes up to first peduncle, variably pubescent in kind and degree, the herbage silvery, cinereous, or green, the leaflets either glabrous or pubescent above; stipules submembranous becoming scarious, pallid or brownish in age, 1.6-10 (12) mm. long, pubescent dorsally, all fully amplexicaul and connate, the smaller lowest ones into a subtruncate or bidentate sheath, the upper progressively longer ones with narrowly triangular or lance-acuminate free blades as long as or longer than the sheathing base; leaves 1-6 (7.5) cm. long, all subsessile or the lowest shortly petioled, with (5) 9—17 (19) elliptic, oblong-elliptic, or oblanceolate, acute, or obtuse and mucronulate, or (in some lower leaves) obovate and obtuse, flat, loosely folded, or involute, crowded or well-spaced leaflets (2) 3-17 (19) mm. long; peduncles divaricate or incurved-ascending, 1-9 cm. long, mostly as long as or longer, rarely shorter than the leaf; racemes at early anthesis rather closely 3-30-flowered, becoming looser, the axis more or less elongating, 0.5-9 (13) cm. long in fruit; bracts submembranous becoming scarious, narrowly ovate to lance-acuminate, 1.5-7 mm. long; pedicels ascending or a trifle arched outward, at anthesis 0.4-1.4 mm., in fruit 0.5-2.2 mm. long; bracteoles 0-2, commonly present but often minute; calyx 3.2-7.6 (8.8) mm. long, pubescent like the herbage with white or sometimes a few black or fuscous hairs, the disc subsymmetric, the subulate or subulate-sectaceous teeth slightly shorter to much longer than the campanulate tube; petals varying from greenish- or pinkish-white to ochroleucous and to lurid or magenta-purple, regularly graduated, or the wings sometimes a trifle longer than the banner; banner abruptly recurved through 50-85°, variable in outline, 5.9-11.8 mm. long, carinate dorsally by the midnerve which often runs out as a minute appendage in the apical sinuses; wings 5.8-10.7 mm. long, the blades oblanceolate, elliptic, or obliquely obovate, obtuse or obscurely emarginate, both incurved but the left one more abruptly so and its inner margin folded over or toward the keel; keel 5.1-10 mm. long, the obliquely triangular blades abruptly incurved through 90-100° to the sharply deltoid to lance-acuminate and beaklike, often slightly porrect apex; anthers 0.4-0.75 mm. long; pod ascending, spreading, rarely a little declined, commonly humistrate, varying from plumply half-ovoid to narrowly oblong-ellipsoid, variably compressed, either rounded or sulcate dorsally, 6-20 mm. long, contracted distally into a deltoid or triangular-acuminate, laterally compressed beak, the thinly fleshy, strigulose or subvillosulous valves becoming leathery or papery, stramineous or brownish, reticulate or nearly smooth, not inflexed; ovules 6-26; seeds dark brown to nearly black, smooth or pitted, sublustrous, 1.7-2.8 mm. long.
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Discussion
The various forms of the polymorphic ground-cover milk-vetch, A. humistratus, fall readily into two main categories or subspecific branches. Disregarding for the moment the very distinct var. crispulus, it is possible to trace a well-defined dichotomy within the species composed of a southeastern branch, which is characterized by relatively long and narrow, pluriovulate pods, and a northwestern one, which is characterized by shorter pods, plumper in profile and relatively few-ovulate. Apart over most of their ranges of dispersal, the forks of the dichotomy are sympatric in some areas of eastcentral and western New Mexico. Within each branch there are parallel variations in the dispersal and density of the vesture, and in each are found a more glabrous and a more pubescent variety which occupy clearly different, although partly overlapping ranges. Varieties based on characters of vesture alone are seldom satisfactory in Astragalus, but in A. humistratus, even though two forms may be found in close proximity, they are not known as yet to intergrade. In the past most authors, always excepting Rydberg, have united all the silvery forms of A. humistratus under the name of var. sonorae, whatever the pod’s shape or length; but they illogically maintained glabrescent vars. Hosackiae and humistratus because of precisely equivalent differences in the fruit. Two more rather striking modifications have occurred in the species: one (our var. tenerrimus) involving reduction in size of all organs; the other, an alteration in the quality of vesture from a stiff and closely appressed type of hair to a weak and sinuous one, which gives Var. crispulus its immediately striking individuality. The species as a whole is set off from all relatives by well-defined boundaries and is easily recognized by the combination of the hair-attachment, connate stipules of thin texture, shallow calyx-tube, and unilocular pod formed on a small scale like that of the commoner species of Argophylli, that is, more or less obcompressed in the body and laterally flattened in the beak.