Astragalus macrodon (Hook. & Arn.) A.Gray
-
Authors
Rupert C. Barneby
-
Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
-
Family
Fabaceae
-
Scientific Name
-
Type
"California, Douglas."—Holotypus, collected in 1833, K! isotypi, BM, G, P!
-
Synonyms
Phaca macrodon Hook. & Arn., Tragacantha macrodon (Hook. & Arn.) Kuntze, Astragalus holosericeus M.E.Jones
-
Description
Species Description - Diffuse, perennial, of moderate stature, with a slender but at length woody taproot and superficial root-crown or shortly forking caudex, densely to rather sparsely villosulous throughout or nearly so with fine, straight and ascending or spreading, or somewhat sinuous and incurved hairs up to 0.5-0.8 (1) mm. long, the herbage greenish-cinereous or canescent, the red-margined leaflets pubescent on both sides, but sometimes thinly so above; stems several or numerous, 1.5-5 (8) dm. long, decumbent and ascending to form low, tufted clumps, branched or spurred at most axils preceding the first peduncle, floriferous upward from near or below the middle; stipules herbaceous, green or reddish, the lowest becoming firmly papery and brownish, 1.5-8 (12) mm. long, amplexicaul-decurrent around ½-¾ of the stem, the lower ones triangular, the upper lance-acuminate, the blades mostly deflexed; leaves 5.5-15 cm. long, shortly petioled, with (11) 17-27 (29) oblong-oblanceolate to narrowly elliptic, or (in some lower leaves) obovate, acute and mucronulate, truncate and mucronulate, or shallowly retuse, flat or loosely folded leaflets (4) 7-22 (25) mm. long; peduncles divaricate or incurved-ascending, 3.5-10 (12) cm. long, shorter than the leaf; racemes loosely (8) 10-30 (35)-flowered, the flowers ultimately declined, the axis elongating, 3-15 (20) cm. long in fruit; bracts thinly herbaceous, narrowly triangular or lance-acuminate, 1.5-3.5 mm. long; pedicels slender, at anthesis ascending, straight, 1-3 mm. long, in fruit a trifle thickened, straight and divaricate or somewhat arched downward, 1.6-4 mm. long; bracteoles 2, minute; calyx 6.5-8.7 mm. long, densely villosulous with white or exceptionally a few black hairs, the oblique disc 1-1.5 mm. deep, the campanulate tube 3.6—4.5 mm. long, 2.7—3.5 mm. in diameter, the firm, lanceolate or subulate, reddish teeth 2.5—4.3 mm. long, the whole becoming papery, ruptured, marcescent; petals pale or greenish-yellow, distally tinged and the banner striate with brownish-red; banner abruptly recurved through nearly 90°, 8.3-11.4 mm. long, the short cuneate claw abruptly expanded into a broadly ovate or suborbicular, shallowly notched or rarely entire and mucronulate blade 5.8—7.8 mm. wide; wings 7.8—10.4 mm. long, the claws 3.3—4.3 mm., the oblanceolate, obtuse-truncate or subemarginate, gently incurved blades 5.1—6.9 mm. long, 2.1—3 mm. wide, the inner margin of the left one infolded; keel 7.5—9.1 mm. long, the claws 3.5—4.3 mm., the broadly half—elliptic or -circular blades 4.7-5.6 mm. long, 2.2-2.8 mm. wide, incurved through 90-95° to the sharply triangular, sometimes obscurely porrect apex; anthers (0.5) 0.55—0.75 (0.8) mm. long; pod loosely spreading or declined, or (when humistrate) apparently ascending, sessile on the conical receptacle, broadly ovoid-ellipsoid, bladdery-inflated, 2-4 cm. long, 1.4-2 (or when pressed seemingly up to 2.3) cm. in diameter, rounded or broadly obconic at base, contracted distally into an erect or gently incurved, shortly deltoid, laterally compressed beak, elsewhere a trifle obcompressed, shallowly sulcate along the ventral or both sutures, the thin, pale green but commonly red-cheeked, sparsely to quite densely villosulous or strigulose-villosulous valves becoming papery, stramineous, delicately cross-reticulate, not inflexed, the funicular flange 0 or up to 1 (1.4) mm. wide; dehiscence apical, after falling; ovules 29-52; seeds (seldom seen) brown, punctate, dull, ± 3 mm. long.
Distribution and Ecology - Open hillsides, sometimes on the site of chaparral bums, and on bare ridges and along gullied draws in grassy hillsides, on shale or sandstone, 750—3250 feet, rare and local but forming colonies, inner South Coast Ranges in California, particularly along the foothills of the middle and upper Salinas Valley, Monterey, San Benito, and northern San Luis Obispo Counties, southeast to the Temblor Range in western Kern County, Caliente Mountain in southeastern San Luis Obispo County, and the north slope of Sierra Madre in northern Santa Barbara County; reported by Jones, probably erroneously, from Fresno.—Map No. 114.—April to June.
-
Discussion
The long-toothed milk-vetch, A. macrodon, is a critical species, resembling (as Jepson, 1936, p. 354, has already pointed out) A. Douglasii in nearly every particular except for the greater density and divergent orientation of the hairs on the leaves and pods. And I must note that the southern A. Douglasii var. Parishii is represented in the San Jacinto Mountains in Riverside County by an almost comparably villosulous minor variant. In addition to the loose pubescence A. macrodon has calyx-teeth averaging but by no means absolutely longer than that of A. Douglasii, a suffusion of brownish-red pigment along the margins of the leaflets and the petal-veins, and fewer ovules (29-52 as opposed to 51-71). These are feeble characters and the species should perhaps be reduced to varietal status, although this course would be highly inconvenient nomenclaturally because of a possible narrow priority of the epithet macrodon. Jepson admitted that little was known of the habits of A. macrodon, but I am now somewhat better informed, field experience having shed light on the ability of the species to maintain itself as a distinct entity within the range of its vigorous and common relative.
In the summer of 1954, as I drove southwest from Bitter Water in southern San Benito County toward King City, my eye was caught by a narrow, vertical stripe of pale vegetation, which stood out in sharp contrast against the dark brush of a steep north-facing hillside. On closer view the stripe resolved itself into a stand of the rare endemic mallow Malacothamnus aboriginum; in the interspaces between the shrubs Astragalus macrodon was abundant. I surmised that the strip of mallow marked the site of a former bum; the adobe topsoil had been washed out, exposing a yellowish shale, and the mallow and astragalus were precisely confined to this formation on which little else had found a foothold. I learned since from Ernest C. Twisselmann, whose knowledge of the flora of the arid inner Coast Ranges in unexcelled, that the long-toothed milk-vetch is found under similar conditions in western Kern County. Mr. Twisselmann writes (June, 1956, in correspondence): "A. macrodon does not occur at all here in the rolling hills of the northern Temblor Range. In the Temblor Mountains, west and north of McKittrick, the colonies are very local in weathered white or light tan shale. Usually each colony consists of relatively few individuals. It is found also in shallow, very light sandy soil around sandstone outcrops. With us it is one of the plants found only at higher elevations, at least 2500 feet in most cases, associated with Douglas oak and California juniper. At the summit of Black Canyon, a scattered colony mixed with an equally sparse colony of A. lentiginosus var. idriensis grows on a pure, rather hard shale ridge top. Only a few feet away, in better soil, A. Douglasii is found. A. Douglasii, of course, grows throughout the region in almost any kind of soil. It is common in adobe and other heavy soils in this immediate area, where A. macrodon is unknown..."
I feel safe in assuming that A. macrodon is adapted to an ecological niche from which A. Douglasii is excluded, and that the tolerances and preferences of the two species are likely controlled genetically. Perhaps the best differential character of A. macrodon is a physiological one.
The range of A. macrodon as shown on the accompanying map is a very natural one, not likely to be greatly extended. Jones (1923, p. 112) reported the species from the floor of the Great Valley at Fresno and described it as dispersed "around the San Joaquin Valley. No specimens confirming this range have been found. I suspect that flowering specimens of A. lentiginosus var. nigricalycis may have been mistaken in the past for what was long a poorly understood and rarely collected astragalus.
-
Objects
-
Distribution
California United States of America North America|