I have collected this species four times and all of the plants were found in old, fallow fields, usually far removed from a railroad. The one in Perry County was found in dry soil in an old, fallow field about 2 miles east of Oriole where it was associated with thick stands of Cassia fasciculata. Pepoon and Umbach report finding two colonies along railroads in the dune area. I think this species has been introduced into Indiana, probably in grass seed or as a railroad waif.
Kearney and Peebles 1969, Martin and Hutchins 1980
Duration: Annual Nativity: Native Lifeform: Subshrub General: Ascending to erect herbaceous annual, simply stemmed or branching from the base, stems and leaves villous with spreading hairs, the stems 10-50 cm tall. Leaves: Unifoliate (single) alternate leaves, leaves linear, lanceolate, elliptic, oval, or obovate, the surfaces villous with spreading hairs, 2-6 cm long, abruptly acute, sessile or nearly so. Flowers: Yellow to slightly orange flowers with the same color banner and keel, the calyx bilabiate, longer than the flowers, covered with spreading hairs, singular flowers borne on peduncles, the lobes of the lower lip about 10 mm long, acuminate, the corolla blade 6-11 mm long. Fruits: Elliptic, inflated pods, 25-40 mm long, light green when young, turning black when mature. Ecology: Found in sandy soils along streams from 4,500-6,000 ft (1372-1829 m); flowers August-October. Notes: Distinguished from Crotalaria pumila by the leaves, C. sagittalis has singular leaves, C. pumila has trifoliate leaves. Two varieties of C. sagittalis occur in Arizona; var. blumeriana has shorter stems, shorter and broader leaflets, tiny or no stipules, and smaller pods, occurring in the Chiricahua Mountains, and var. fruticosa, which is somewhat shrubby with a woody base, and uniformly linear leaves (rare). Ethnobotany: The roots were used as a blood purifier and to treat venereal disease, and were considered a strong narcotic. Etymology: Crotolaria is of uncertain origins, while sagittalis likely comes from the Latin for arrow. Synonyms: Many, see Tropicos Editor: LCrumbacher, 2011
Cal obscurely bilabiate, the upper lip less deeply cleft than the lower and with broader lobes; standard suborbicular, short-clawed; wings not auriculate; keel-pet connivent on both margins, strongly convex on the lower side; stamens 10, monadelphous below the middle, the sheath cleft on the upper side; filaments alternately long with subglobose anthers, and short with linear anthers; distal part of the style usually with 1 or 2 lines of hairs; pods subglobose to cylindric or ellipsoid, inflated; seeds 2-many; annual or perennial herbs, or shrubs in the tropics, with simple (in all our spp.) or trifoliolate lvs and usually yellow fls in racemes. 600, mostly warm reg.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.