Infrequent in dry, clayey soil on white oak and black and white oak slopes and ridges and less frequent in post oak "flats" in southwestern Indiana. In the northwestern part of the state it is found in dry, sandy soil on black and white oak ridges and rarely on aspen flats about lakes and in the prairie area. Its habitat suggests a slightly acid soil or one low in fertility.
Stems 1-few, erect or ascending, simple or virgately branched above, strigose, 3-10(-15) dm; lvs usually erect or strongly ascending; lfls linear to narrowly oblong, 3-5(-7) mm wide, (3-)4-6 times as long, short-strigose on both sides, or rarely glabrous above; fls purple, 6-8 mm, the apetalous ones chiefly along the middle of the stem in small, subsessile clusters, the others in short, few- fld racemes from the upper axils, on peduncles shorter than the lvs, forming a crowded, leafy infl; cal-lobes of the petaliferous fls 1.7-3 mm, the 2 uppermost connate to the middle or beyond; fr thinly and inconspicuously strigose; 2n=20. Dry upland woods; Mass. and Vt. to Wis., s. to n. Fla., Kans., and Tex. Aug., Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.