Infrequent to rare in the southern counties on bare, open places on ridges wooded with black and white oak. Found also in a few post oak flats in the extreme southwestern counties. [Deam describes S. biflora var. hispidissima as having more or less densely hispid stem and leaf margins. in addition,] plants of the variety are larger, erect or nearly so, and with longer leaflets. My Crawford County specimen is from a dry woods near Wyandotte Cave, and the Daviess and Knox County specimens are from sand hills. I have not ascertained the range of the variety.
Stems wiry, branched from the base, depressed to ascending or erect, 1-5 dm, with or without spreading setae; lfls narrow, 1-4 cm, 3-6 times as long as wide, acute and subulate-tipped to merely mucronate; spikes short; bracteal lvs usually 1-foliolate, the blade and stipular base often setose-ciliate as well as puberulent; fls 2-6 in the spike, orange-yellow (white), the standard 7-9 mm; fr 4-5 mm, thinly hairy, obliquely ovate, reticulate-veiny; 2n=20. Dry or rocky woods and barrens; s. N.Y. to O., s. Ill., and Kans., s. to Fla. and La. June-Aug. (S. riparia)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.