Very slender, ephemeral, sparsely leafy annual, with a filiform taproot, thinly strigulose with appressed hairs up to 0.25-0.4 mm. long, the herbage green, the leaflets glabrous above, the inflorescence fuscous- or black-strigulose; stems solitary and erect or more commonly 2-3, the lateral ones ascending from the axils of the cotyledons (these oblanceolate, obtuse, 9—11 mm. long) or from the first node, simple or (in some vigorous plants) branched near the base, (2) 3-10 (23) cm! long, floriferous from 2—4 (6) distal nodes; stipules submembranous, pale green or purplish becoming papery and pallid or brownish in age, broadly ovate or ovate-acuminate, 1-2.5 (3) mm. long, about semiamplexicaul, glabrous dorsally, all but the lowest sparsely black- or fuscous-ciliate; leaves 1.5-5 cm. long, with slender petioles and 5—9 cuneate-obovate to narrowly cuneate, deeply retuse, flat, rather distant leaflets 2—10 mm. long; peduncles at first ascending, declined or divaricate in age, 2—7 cm. long, surpassing the leaf; racemes subcapitately 2-7-flowered, the flowers becoming horizontal and at last declined, the axis scarcely elongating, 2—10 (13) mm. long in fruit; bracts submembranous, ovate, 0.7-1.2 mm. long; pedicels at anthesis ascending or a little arched outward, 0.4-1 mm. long, in fruit straight and widely ascending or arched outward, a little thickened, 0.8—2.2 mm. long; bracteoles 0; calyx 2.8—4 mm. long, densely strigulose with black or dark brown hairs, the subsymmetric disc 0.5-0.8 mm. deep, the tube 2.1—2.6 mm. long, 1.6—2.3 mm. in diameter, the broadly subulate or triangular, obtuse teeth 0.6—1.4 mm. long, the whole becoming papery, marcescent unruptured; petals bicolored, whitish but the distal third of the banner and the keel-tip maculate with dark lilac, drying violet; banner recurved through only 20°, 8.9-12 mm. long, the short, cuneate claw expanded into a broadly oblong-elliptic or ovate-oblong, openly and shallowly emarginate blade 4.8-6 mm, wide; wings 6.7-9 mm. long, the claws 1.6-2.3 mm., the linear-oblong, oblong, or oblong- elliptic, obtuse or obliquely truncate blades 5.5-7.5 mm. long, 1.5-2.4 mm. wide; keel as long or commonly a little (0.2-1.5 mm.) longer than the wings, 7.4-9.1 mm. long, the claws 2.1-2.7 mm., the obliquely triangular blades 5.7-7.2 mm. long, 2.8-3.5 mm. wide, abruptly incurved through (85) 90° to the broad, rounded apex; anthers 0.4-0.5 mm. long; pod horizontal or declined, sessile but elevated on and disjointing from a slender gynophore 1.4—2.5 mm. long, also pseudostipitate, the narrowly crescentic body 1.7-2.5 cm. long, (1.6) 2-3.1 mm. in diameter at or near the middle, long-attenuate at both ends, at base into a straight, slender, sterile, stipelike portion, distally into a long-subulate, strongly incurved or hooked beak, at the middle obscurely triquetrous, obtusely carinate ventrally by the suture, rounded dorsally, the thinly fleshy, green or faintly brown- mottled valves becoming stiffly papery and brownish, finely strigulose with white and often a few black hairs, inflexed as a complete or nearly complete septum; ovules 6-12; seeds brown, sparsely pitted, dull, 2.7-3.3 mm. long.—Collections: 7 (ii); representative: J. T. Howell 6431 (CAS, MO, POM), 6442 (CAS, GH, K, US); Mrs. Hunt (from near St. Helena) in 1922 (CAS); Barneby 11,238 (CAS, NY, POM, RSA); Jepson 13,756 (UC-JEPS).
Open grassy hillsides, especially on exposed shoulders in thin volcanic clay soil moist in spring, 300-550 feet, rare and local, known only from the inner North Coast Range about St. Helena and Santa Rosa, in Napa and Sonoma Counties, California.—Map No. 148.—April to May.
Astragalus Clarianus (Clara A., Mrs. D. O. Hunt, the collector, a correspondent of Jepson) Jeps., Man. Calif. 578, fig. 570. 1925 ("clarianus").—"Napa Range: near St. Helena (Clara A. Hunt, type)."—Holotypus, "received April 8, 1909," UC-JEPS!—A. Rattani var. Clarianus (Jeps.) Jeps., Fl. Calif. 2: 379. 1936 ("Clarianus"). Hamosa Clariana (Jeps.) Rydb. in N. Amer. Fl. 24:427 (quoad nom.). 1929.
The Napa milk-vetch, A. Clarianus, in most features nearly resembles and is probably derived by mutation from A. Rattani var. Jepsonianus or an immediate common precursor; of the two it is clearly the more highly modified organism. The petals of both species are (in var. Jepsonianus inconsistently) bicolored, remarkable for the vivid anthocyanic band or border painted across the distal third of the banner and the keel-tip, in contrast to the whitish or palest pink wings and claws. In both the extremely narrow, elongate pod is attenuate at either end, at apex into a long-subulate, cusplike beak, and at base into a sterile, stipelike neck. But the Napa milk-vetch differs greatly in the relative proportions of the petals and is instantly recognized by the prominent broad keel which equals or ordinarily shortly surpasses the narrow wings. The flower resembles, to a surprising degree, that of the wholly unrelated A. alpinus. Furthermore the pod, although technically sessile as in A. Rattani, is elevated out of the bed of the calyx on a slender, stipelike gynophore and, with its attenuate sterile base, is doubly pseudostipitate, a combination unique in the genus so far as my knowledge goes.
The Napa milk-vetch is among the rarest of California’s many endemic astragali, known probably from only three localities, although one of them extends interruptedly over an area of two or three square miles. It is recorded only from near St. Helena; from Conn Valley, Napa County, now the site of the reservoir Lake Hennessey; and from points about seven or eight miles northeast of Santa Rosa on the old Spring Valley road to St. Helena where it was still locally plentiful until a few years ago. The whole known range of var. Clarianus does not exceed fifteen miles in diameter. The more extensive dispersal attributed to the species by Rydberg (1929, p. 427) and Abrams (1944, p. 603, fig. 2895) was based on confusion with A. Rattani var. Jepsonianus.