Monographs Details: Astragalus distortus var. engelmannii (E.Sheld.) M.E.Jones
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.

301b. Astragalus distortus var. Engelmanni

Closely resembling var. distortus, usually quite slender; calyx 3-4.5 mm. long, the tube (2) 2.4-3.4 mm. long, 1.8-2.3 (2.5) mm. in diameter, the teeth 0.7-1.5 (1.8) mm. long; petals purple with pale or whitish wing-tips; banner 8.2-11.6 (12) mm. long, 4-6.9 mm. wide; wings 7-9.8 mm. long, the claws 2.5-3.2 mm., the blades 5-7.7 mm. long, 1.6—2.5 mm. wide; keel 5.5-7 (7.2) mm. long, the claws 2.5—3.4 mm., the blades 3.3-4.5 mm. long, 1.8—2.4 mm. wide; pod 1.3-2 cm. long, 3.5-5.5 (6) mm. in diameter, gently or quite strongly incurved, often widest a little above the middle and subclavate-oblanceolate in outline.—Collections: 67 (ii); representative: Tharp & Barkley 47,138 (SMU, TEX, WS); G. Fisher (from Houston) in 1930 (CAS, OKLA); Cory 55,520 (SMU, WS); Tharp (from Ballard, Texas) in 1933 (NY, TEX); E. J. Palmer 7077 (CAS), 11,455 (NY), 13,155 (WIS); Shinners 11,171, 14,346 (SMU).

Habitats of var. distortus, usually in open pine or oak woods, common and locally plentiful in eastern Texas, from the San Antonio River in Goliad County and Matagorda Bay north to Fort Worth and the northeast comer of the state, extending just into northwestern Louisiana and (presumably adjoining) Arkansas. —Map No. 138.—(February) March to May. Astragalus distortus var. Engelmanni (Sheld.) Jones, Rev. Astrag. 256, Pl. 65. 1923, based on A. Engelmanni (George Engelmann, 1809-1884, physician and preeminent XlX-century botanist) Sheld. in Minn. Bot. Stud. 1: 152. 1894.—"Collected on the Brazos, Texas, April 1839, February 1844. Also in open woods near Houston, Texas, March, 1842, by Ferdinand Lindheimer... "—Holotypus, Lindheimer 70, from Houston, in February, 1844, MO (2 sheets); probable isotypi, Lindheimer from Houston, numbered No. 414, SMU! and from Brazos, dated April, 1844, NY! paratypi, Lindheimer in April, 1839, and in March, 1842, MO! —Holcophacos Engelmanni (Sheld.) Rydb. ap. Small, Fl. S. E. U. S. 1332. 1903.

The Engelmann milk-vetch, the commonest perennial astragalus of the wooded sections of eastern Texas, is distinguished from var. distortus mainly by its slightly smaller flower and usually fewer-ovulate pod. The average pod is a little shorter and proportionately wider than that of var. distortus, and when ripe it is ordinarily sulcate only along the dorsal suture. Occasional specimens (e.g., L. McLean in 1933, OKLA, from near the variety’s south limit in Bexar County) combine the short flower of var. Engelmanni with the long, narrow, bisulcate fruit of var. distortus. The pod of var. Engelmanni is similar in form to that of A. obcordatus, native farther east along the Gulf Coastal Plain from Mississippi to Florida, but is less prominently reticulate when ripe; and the petals are more strongly graduated, with keel very much shorter than the banner. The differential characters of the closely related and sympatric A. Soxmaniorum are mentioned under the next species.

Although so common in eastern Texas, the Engelman milk-vetch extends rarely beyond the state borders. Only one collection (F. L. Harvey in 1883, WS) has been seen from Arkansas, and since this lacks precise locality data, the record is omitted from the map. Jones (l.c.) reported the variety from Oklahoma, but the Carleton specimens from the Indian Territory (Vinita, Oklahoma, No. 30, NY) are typical var. distortus. The earliest collections of var. Engelmanni, brought back from Texas by Drummond and Leavenworth, formed part of the original concept of A. distortus T. & G. A Nuttall collection, apparently representing var. Engelmanni but of uncertain provenance, is mentioned in Appendix I under A. debilis Nutt.