Astragalus lentiginosus var. araneosus

Title

Astragalus lentiginosus var. araneosus

Authors

Rupert C. Barneby

Scientific Name

Astragalus lentiginosus var. araneosus (E.Sheld.) Barneby

Description

289s.  Astragalus lentiginosus var. araneosus

Perennial, low but relatively coarse, strigulose with straight, usually appressed hairs up to 0.4—0.7 mm. long, commonly thinly so, the herbage green, the leaflets glabrous above or on both sides, ciliate, more rarely thinly pubescent on both sides and greenish-cinereous; stems several or numerous, diffuse and incurved-ascending, 2.5 (3.5) dm. long, often red-tinged, simple, floriferous upward from near or below the middle; leaves (2.5) 4-11 cm. long, with 15-23 elliptic-oblanceolate, broadly oblong-oblanceolate, or obovate, obtuse or emarginate, flat or loosely folded leaflets (3) 5-17 (20) mm. long; peduncles stout, 2.5-6 (7.5) cm. long; racemes 10-20-flowered, the axis 1.5-4 (5.5) cm. long in fruit; calyx (6.2) 7.5-10.5 mm., the tube (4.6) 5.2-6.7 mm. long, (2.4) 2.8-3.4 mm. in diameter, the teeth 1.4-3.8 mm. long; petals bright pink-purple, the banner with a pale, striate eye; banner (12.5) 15-18.2 mm. long, 7-10.4 mm, wide; wings (10.3) 12.7-16 mm., the claws (4.5) 6.6—8 mm., the blades (6.5) 7—9 mm. long; keel (9) 10.5-15 mm. long, the claws (4.6) 6.5-8.1 mm., the blades (4.6) 6-7 mm. l°ⁿgj (2.3) 2.7—3.1 mm. wide; pod very obliquely ovate-acuminate in profile, 1.5-3 (4) cm. long, (7) 9-15 mm. in diameter, almost always very strongly incurved, the moderately or greatly inflated body tapering or abruptly contracted into an incurved, unilocular beak 6—15 mm. long, the green, often red-mottled, glabrous or rarely puberulent valves becoming stiffly papery or almost leathery, the complete septum about 3-5.5 mm., the funicular flange 0.8-2 mm. wide; ovules 24-34 (38).—Collections: 39 (viii); representative: Maguire & Blood 4411 (F, POM, UC); Eastwood & Howell 622 (CAS, NY, POM), 9340 (CAS, RSA, WS); Ripley & Barneby 3575 (CAS, RSA); C. L. Hitchcock 2957 (F, WS, WTU); Jones (from Detroit, Utah) in 1891 (POM, UC).

Gravelly banks, washes, gullied foothills, and valley floors, with sagebrush or juniper, commonly but not exclusively in alkaline soils, apparently most abundant on calcareous bedrock but not confined thereto, 4700-7200 feet, forming colonies and sometimes locally abundant, widespread over western Utah from Salt Lake and Wasatch Counties south to Iron County, and ascending the Sevier Valley into Piute County, west across the Salt Lake and Sevier Deserts into the valleys of northeastern and central Nevada, there apparently intergrading with vars. Fremontii, Kennedyi, and toyabensis.—Map No. 131.—May to July.

Astragalus lentiginosus var. araneosus (Sheld.) Barneby in Leafl. West. Bot. 4: 112, Pl. III, figs. 11-14. 1945, based on A. araneosus (cobwebby, in allusion to the filaments within the pod) Sheld. in Minn. Bot. Stud. 1: 170. 1894.—"Collected near Frisco, Utah, June, 1880, by M. E. Jones; also at Muddy station, John Day valley, Oregon, May, 1885, by Thomas Howell."—Lectotypus (Barneby, l.c.), Jones 1807, MINN! isotypi, F, GH, NY, ORE, POM, RM, US! (the paratypus = var. platyphyllidius).—A. palans var. araneosus (Sheld.) Jones in Proc. Calif. Acad. Sci. II, 5: 675. 1895. Cystium araneosum (Sheld.) Rydb. in Bull. Torr. Club 40 : 50. 1913.

The var. araneosus is the commonest freckled milk-vetch dispersed over the bed of former Lake Bonneville, whence it extends westward into the mountain valleys of eastern and central Nevada and southward some distance up the canyon of the Sevier River. Over the greater part of its area it is the only representative of the species with purple flowers of good size and pods of leathery or stiffly papery texture, features shared, however, by the rare var. latus (which differs in its subglobose pod with very short, bilocular beak) and by the allopatric but very closely related var. diphysus. The latter is rather artificially separated from var. araneosus by pronounced tendencies in variation rather than by any one differential character: the plants are more often glabrous or nearly so, while the pod is less oblique in profile with a shorter and less strongly incurved beak. At the time of my revision of A. lentiginosus (1945) var. diphysus had not been found north or west of the Colorado River in northern Arizona. It has since been traced to the Henry Mountains in southern Utah, and it is possible that the two varieties will prove to be geographically as well as morphologically confluent.

The var. araneosus is no less variable than other widespread forms of its species. The pod varies greatly in the degree of inflation and in the least-swollen state nearly approaches that of var. palans (see discussion below). Ordinarily the flowers are quite large and handsome, with calyx about 7.5-10.5 mm., banner 15-18 mm., and keel well over 10 and up to 15 mm. long; but at the southwest edge of its range in central Nevada are encountered (mostly on granitic or volcanic rock-formations) populations with rather small flowers (the calyx about 6.2-7 mm., banner 12.5-15 mm., and keel about 9-10 mm. long) combined now with short and now with moderately elongating raceme-axis, and pods intermediate in texture between stiffly papery and papery-membranous. Plants of this nature are in various degrees intergradient between var. araneosus as ideally conceived and the vicariant vars. Fremontii, Kennedyi (both long-racemose, the former even smaller-flowered), and toyabensis (short-racemose but with thin-papery pod). Cf. Ripley & Barneby 3652, 4427, 6234, from Nye and Eureka Counties (RSA).