Monographs Details: Astragalus distortus Torr. & A.Gray var. distortus
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:

301a. Astragalus distortus var. distortus

Habit of the species; calyx-tube 2.8-3.8 mm. long, 2.1-3.2 mm. in diameter, the teeth 1.2—1.9 (2.5) mm. long; banner (10.5) 11-15.5 mm. long, (4.2) 5.2 8.4 mm. wide; wings (9) 10-13.7 mm. long, the claws (2.5) 3-4.1 mm., the blades (6.6) 7.6-9.8 mm. long, 2-3.5 mm. wide; keel (7) 7.4-9.3 mm. long, the claws (3) 3.3—4.2 mm., the blades 4.3—5.7 mm. long, (2.1) 2.3—3 mm. wide; pod 1.3—2.5 cm. long, 4—7 mm. in diameter.—Collections: 83 (ii); representative: Hopkins & A. & R. Nelson 1023 (SMU, TEX, WIS); Goodman & Waterfall 4703 (OKLA, TEX); Barneby 12,586 (CAS, NY, RSA), 12,587 (CAS, RSA); Demaree 21,978 (CAS, NY); Small & Wherry 11,759 (NY); Horr 3604 (CAS, OKLA, TEX, WS).

Prairies, pastures, gullied stream banks, and sandy or sandy clay flats in open pine and oak woods, widespread and locally plentiful in Oklahoma, Missouri, and extreme southeastern Kansas, north (becoming rarer) to Iowa and central Illinois, and known from outlying stations (possibly introduced) in southern Louisiana and eastern Mississippi; greatly isolated, on shale barrens and in shaley pastures, in the foothills of the Allegheny Mountains in western Maryland, northern Virginia, and northeastern West Virginia.—Map No. 138—Late March to July.

Astragalus distortus (twisted, of the pod) T. & G., Fl. N. Amer. 1: 333. 1838.— "Arkansas, Nuttall! Dr. Leavenworth! Texas, Drummond! Dr. Leavenworth!"—Lectotypus, labeled in Nuttall’s hand "Astragalus obcordatus Ell. Arkansa.," NY! The Texan paratypi represent var. Engelmanni; isotypi, labeled by Nuttall "Phaca *humifusa. Ark.," PH, "Astragalus *arkansanus." G, and "Astragalus ... quite new ... Nuttall. Ark.," PH!—Tragacantha distorta (T. & G.) O. Kze., Rev. Gen. 944. 1891. Holcophacos distortus (T. & G.) Rydb. ap. Small, Fl. S. E. U. S. 1332. 1903.

Astragalus distortus fma. albiflorus (white-flowered) R. L. McGregor in Trans. Kans. Acad. Sci. 60: 161. 1957.—"... 8 miles west of Weir, Cherokee County, Kansas, April 30, 1955, R. L. McGregor 9935."—Holotypus (KANU), not examined.

The Ozark milk-vetch, var. distortus, is variable in color of the petals which change, from one population to the next, from a lively pink-purple to a lilac so pale as to seem white in bright sunshine; true albinism occurs more rarely, when the plant loses the last trace of anthocyanic pigment and the stems and herbage assume a characteristic pallor. The fma. albiflorus described from Bourbon, Crawford, and Cherokee Counties in Kansas is probably the pallid rather than the full albino phase.

The populations of A. distortus isolated from the main range of the species in northeastern West Virginia and adjoining states probably represent a distinct race, although this seems too little modified morphologically to deserve taxonomic notice. The flowers are on the small size of normal for var. distortus, thus approaching var. Engelmanni. The narrow, bisulcate pod, however, seems not to differ from that of the Ozark plant except that the ovules are fewer, 18-26 as opposed to 28-36.