Monographs Details: Astragalus nuttallianus var. austrinus Barneby
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
Discussion:

333f. Astragalus Nuttallianus var. austrinus

Usually very slender, often diminutive and fleeting, the stems mostly (0.1) 0.3-2.5 (3.5) dm. long, the herbage gray- or silvery-strigulose or -hirsutulous, often densely so; leaves 1—6.5 cm. long, with about 7—11 small, narrowly elliptic leaflets, those of the lowest leaves sometimes broader but never truncate-emarginate; racemes mostly (1) 2—5 (7)-flowered; calyx mostly 3.7—5.4 mm. long, the teeth silvery-pilose with lustrous, spreading hairs mostly over 0.65 mm. long; petals whitish or pale purple; flowers as in the preceding two varieties but always small, the banner (4) 5.5-7 mm. long; pod as in var. pleianthus but either glabrous or strigulose with closely appressed hairs up to 0.5 mm. long.—Collections: 113 (xiii); representative: A & R. Nelson 1438 (NY, SMU); Metcalfe 1531 (CAS, NMC); Barneby 12,592 (CAS, RSA); Waterfall 7800 (OKLA, TEX); B. L. Turner 838 (SMU, SRSC); Cory 53,400 (SMU, WS); Earle & Tracy 190 (NY); Palmer 26 (NY, US); Hartman 595 (NY, US); Pringle 276 (NY, US), 853 (NY); Arsene 3622 (US).

Dry plains and hillsides, sometimes abundant along roadsides, in various types of dry, heavy or porous soils, especially common and vigorous on limestones, mostly above 2000 and up to 7000 feet (lower only in isolated stations eastward), widespread and common nearly throughout the Pecos Valley, western Texas and eastern New Mexico north to Quay and Guadelupe Counties, north through westcentral Texas into southwestern and Panhandle Oklahoma, west through southern New Mexico (and north along the Rio Grande rarely to Albuquerque) into southeastern Arizona, south into northeastern Sonora, Durango, and Nuevo Le6n; apparently isolated on dry limestone hills, about 6500 feet, in Puebla; also, perhaps adventive from farther west, in sandy ground at low elevations in southern Texas (Kenedy Comity).—Map No. 150.—March to May, sometimes again in summer or fall in areas of summer rainfall.

Astragalus Nuttallianus var. austrinus (Small) Barneby ap. Shreve & Wiggins, Veg. Fl. Son. Des. 709, 1964, based on Hamosa austrina (southern) Small, Fl. S. E. U. S. 618, 1332. 1903.—"Type. Rio Fronteras. Texas, Thurber, no. 417, in Herb. N. Y. B. G."—Holotypus, collected in June, 1851. NY! isotypi, giving the state as Sonora (not Texas, as inferred without basis by Small), GH, NY.—Astragalus austrinus (Small) Schulz, Five Hundred Wild Fl. San Antonio 104. 1922.

Astragalus Nuttallianus var. canescens T. & G. ex Wats., Bibl. Ind. 198. 1878, nom. confus. (vide infra).

Astragalus subuniflorus (about 1-flowered) Greene, Leafl. Bot Obs. 2: 42. 1910.—"Near Tehuacan, Puebla, Mexico, 7 Aug. 1897, Pringle no. 6678 as in my set of that collector’s plants."—Holotypus, ND! isotypi, MO, NY, POM. US!—Hamosa subuniflora (Greene) Rydb. in Bun. Torr. Club 54: 328. 1927.

Hamosa davisiana (of the Davis Mountains) Rydb. in Bull. Torr. Club 54: 328. 1927 ("Davisiana").—"The type was collected in the Davis Mountains, Texas, April 28, 1902, Earle & Tracy 329 ... "—Holotypus, NY! isotypi, GH, ND, US!—Astragalus davisianus Greene ex Rydb., 1. c., in syn.

The var. austrinus is the common small-flowered milk-vetch in Texas westward from the Edwards Plateau, in New Mexico southward from Albuquerque and Santa Rosa, and in southeastern Arizona, whence it extends southward, apparently somewhat interruptedly, into central and southern Mexico. Intergradation with var. trichocarpus eastward, and with var. micranthiformis in central Arizona and the upper Rio Grande valley, has already been mentioned. Westward from central Arizona, where it is found in typical form together with var. imperfectus, there is also a zone of intergradation with these two forms; and it apparently passes into var. cedrosensis also in northern Sonora. Over the great part of its range var. austrinus is similar in most respects to var. trichocarpus, although usually of more delicate mien and with only 3-5 pairs of narrowly elliptic leaflets in most mature leaves. It varies in habit of growth according to the season and the type of soil. In dry springs, in sandy soils, and in desert climates, the commonly ascending stems and peduncles tend to become subfiliform and the flowers exceptionally short and pale in coloring; plants rooting in hard-packed or well-watered soils at greater elevations are likely to be prostrate and stouter-stemmed. Ordinarily appressed, the gray or silvery vesture of the leaves and stems is sometimes looser, and a densely silvery-hirsutulous form, not uncommon in trans-Pecos Texas where it is associated with and passes into a more normal type of plant, has been described as Hamosa davisiana but deserves no more than passing mention. Some young plants of var. austrinus (as of other varieties of the species) assume a peculiar aspect when all the peduncles are subfiliform and bear only one or two terminal flowers; the typus of A. subuniflorus was of this nature. The apparent isolation of the latter in Puebla, so far smith of the known continuous range of var. austrinus, suggests the probability of a distinct form; but not only Pringle's but subsequent collections from the same general area can be matched closely by material from southern Arizona and New Mexico (cf. Peebles 11,334, POM). Possibly var. austrinus is introduced in Puebla, although three collections made over a period of years argue its naturalization there. I have interpreted two collections from the Gulf Coastal Plain in southern Texas as probably adventive also.

Unlike the eastern Texan varieties of A. Nuttallianus described up to this point, in which the pod is consistently either glabrous or pubescent, both states occur with about equal frequency In var. austrinus. A feature easily observed and very often significant in the genus, the presence or absence of hairs on the fruit has captured the attention of botanists and has been overemphasized as a differential character. Although it is most uncommon to find glabrous and strigulose pods in one colony of plants in the field (they are more often mixed in herbaria), small colonies of both sorts are frequently found scattered here and there within a plot of a few acres. The members of these nearly sympatric colonies often resemble one another precisely in other characters which are variable in the variety as a whole. Bearing in mind that var. imperfectus and var. micranthiformis vary in the same manner, yet in their discrete ranges peripheral to that of the complex are even more clearly monophyletic, I must regard the pubescence-varients of var. austrinus likewise as insignficant formae.

The var. austrinus, first encountered during the pioneer explorations of August Fendler and Charles Wright in the middle of the last century, has become to western botanists the best-known form of A. Nuttallianus. Gray at first tried to sort out the minor variants, but gave up the attempt as early as his revision (1864, p. 199) wherein all are included in a comprehensive and polymorphic species. As material of var. austrinus accumulated in herbaria under the name of A. Nuttallianus, the circumscription and identity of the original species were forgotten, and by a shift of emphasis the present variety became for Jones (1898, p. 22; 1923, p. 269) the typical and our var. Nuttallianus a subordinate variety (vars. enneajugus and quadrilateralis). This error was corrected by Rydberg (1927, p. 325), who had more direct access to pertinent type-material. Rydberg, however, not only interpreted the glabrous and pubescent fruiting phases of var. austrinus as separate species of Hamosa, but included in the pubescent H. austrina elements of our var. trichocarpus and in the glabrous H. Emoryana an important, in fact lectotypical element of a distinct species, A. Emoryanus of this account. The latter, which is sometimes associated with the glabrous-fruiting mutant of var. austrinus, is quickly separated by its retuse leaflets, blunt keel-tip, and early deciduous pod.

For nomenclatural purposes I have ignored A. Nuttallianus var. canescens T. & G. ex Wats., although it was clearly based in part on the present variety and could possibly be revived for it. Its history is rather curious. As a valid proposition it dates back no further than to Watson’s Bibliographical Index, where it is simply listed with references to T & G. in Pac. R. R. Rep. 2: 163 and to Parry in Amer. Nat. 9: 270: Watson mentioned as synonymous some unnamed varieties of A. Nuttallianus described by Gray in Plantae Wrightianae (1: 52 & 2: 43). The Parry reference is irrevelant as it involves no description and is concerned with a collection of var. imperfectus from southern Utah. Turning to the Railroad Report, we find again simply listed by Torrey & Gray an ‘‘A. Nuttallianus DC. var. trichocarpus & canescens, Gray, Pl. Wright... "; it is clear that we have to go further back for a validating description. In the first volume of Plantae Wrightianae, Gray listed a collection of Wright’s from New Mexico (in 1851) with a Latin phrase describing a dwarf, canescent plant with rather short pods similar to those of var. trichocarpus but glabrous; and he remarked that Fendler’s No. 156 was nearly the same. Unquestionably this constituted the first description of var. austrinus, although Gray made no formal proposition. In the second volume dealing with Wright’s plants (1853) no less than three forms of A. Nuttallianus were distinguished, again without names but with descriptive phrases, from among three sets of numbered specimens (Wright 1001, 1359, 1360) involving collections from at least seven localities in western Texas, New Mexico, and northern Chihuahua. Whether these collections were kept separate by Wright and afterward renumbered and distributed without data or with inexact data by Gray (a common practice at the time) they are now hopelessly muddled. The material extant under these Wright numbers in the Gray and Torrey herbaria includes elements of A. austrinus with glabrous and with pubescent fruit, and a good sprinkling of A. Emoryanus which has only recently been appreciated as a distinct species. The first form mentioned by Gray in Plantae Wrightianae Vol. 2 is based on a mixture of A. Emoryanus (its holotypus) and pubescent var. austrinus. The second is supposedly the same as the var. first mentioned in Pl. Wright. Vol. 1, but the description now calls for a cinereous-hispidulous (not glabrous) pod; it is evidently wholly var. austrinus, as is the third, a very tiny form with diffuse stems and short pods from Lago Santa Maria in Chihuahua, characteristic of plants growing in the stiff soil of a desert playa. Since var. canescens T. & G. was never really proposed by Torrey and Gray, and at best is based on descriptions of two species not distinguished correctly even at the level of unnamed forma, it seems wise to discard it as a confused name.