Monographs Details: Astragalus mohavensis var. hemigyrus (Clokey) 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:

318a. Astragalus mohavensis var. hemigyrus

Flowers slightly smaller than in var. mohavensis, the calyx 4-5.7 mm., its tube 2.5-3.2 mm. long, 1.7-2.4 mm. in diameter, the teeth 1.5-2.5 mm. long; banner 7-9 mm. long, 4.4-5.6 (6.2) mm. wide; wings 6.3-7.8 mm. long, the claws 2-2.9 mm., the blades 4.6-5.4 mm. long, 1.5-2.1 mm. wide; keel either slightly longer or shorter than the wings, the claws 2.4-3.3 mm., the blades 4-5.3 mm. long, 2.2-2.8 mm. wide; pod as described in the key; seeds 2-2.5 mm. long. —Collections: 6 (ii); representative: Jones (topotypus) in 1906 (DS); Clokey 7996 (NA, NY, WS); Clokey & Clokey 8593 (NA, NY, WS); Ripley & Barneby 3772 (CAS, GH, NY, RSA).

Rock ledges and arid gravelly hillsides in the Larrea belt, on limestone, 4100-5200 feet, rare and local, known only from near Indian Springs in the east foothills of the Charleston Mountains, Clark County, Nevada, and from Darwin Mesa, Inyo County, California.—Map No. 144.—April to June.

Astragalus mohavensis var. hemigyrus (Clokey) Barneby in El Aliso 2: 207. 1950, based on A. hemigyrus (half-coiled, of the hooked pod) Clokey in Madrono 6: 220, Pl. 27, figs. p-z. 1942.—"...south of Indian Springs ... April 18, 1939, Clokey 8409 (type)."—Holotypus, collected by C. B. & I. W. Clokey, UC (Herb. Clokey.)! isotypi, K, MINN, NA, OB, PH, RM, SMU, TEX, UC, US, WIS, WS!

The var. hemigyrus is listed first in order because the trigonously compressed fruit is less highly modified than that of var. mohavensis, even though the rarity of the form and what is known of its dispersal suggest to the contrary a recent origin through mutation back to a more primitive type. The two known populations are in close agreement in every characteristic up to and including the flower, but differ somewhat in the form of the fruit. In the type-locality the pod is strongly and evenly incurved, or sometimes more abruptly hooked, the body describing at least half a circle; it is gradually attenuate at base, and the dorsal sulcus is closed or nearly so. In the plants from Darwin Mesa the pod is only crescentically incurved, cuneate at base, and more shallowly and openly sulcate. This variation is no greater, however, than that described below for var. mohavensis, and it seems logical to associate under the present name the two populations which have in common small flowers and dorsally grooved fruits. The two known stations lie within or at the edge of the established range of var. mohavensis and about one hundred miles apart. It is conceivable that they represent independent but nearly parallel modifications arising from the more widely dispersed Mohave milk- vetch. The pod on the plants from Darwin Mesa is not greatly different from the narrowest examples furnished by var. mohavensis, where the dorsal suture, normally prominent and keellike at maturity, becomes perceptibly depressed. It is possible and even probable that further collecting in southern Nevada will show var. hemigyrus to be commoner than is known today.

The var. hemigyrus was first collected at the type-locality by Marcus Jones in 1906, but was mistaken by him for the related A. albens. The description of the latter in Jones’s Revision (1923, p. 261) applies chiefly, that of the pod entirely, to var. hemigyrus, although the fruit illustrated on Plate 66 is that of var. albens.