This is an introduced species that has spread with remarkable rapidity. So far it is restricted to the southern part of the state, our most northern report being from Howard County. I have been well acquainted with the Clark County State Forest of 2,000 acres since 1909. This species was never sown on the cleared land of the forest or in the neighborhood. It appeared spontaneously in the abandoned fields and soon formed dense stands over acres. The forest is so located that the seed could not have been brought in by water. I have no data as to when I first noticed it there. Its sudden and widespread appearance in Indiana is an interesting problem in distribution. Most of my specimens date from 1911-1920. It is usually found in hard, clayey soil, either moist or dry, in open woodland pastures, and fallow fields and along roadsides and railroads. It has been a boon to the grazing industry in that part of the state since it does not appear until August and September and continues until late in autumn.
Indiana Coefficient of Conservatism: C =null, non-native
Annual, erect or diffuse, much branched, 1-4 dm; stems sparsely pubescent with retrorsely curved or appressed hairs; petioles 1-2 mm; lfls oblong-obovate, 1-2 cm, a third as wide; stipules lance-ovate, brown, scarious, many-nerved, persistent, 4-6 mm; fls pink or purple, 1-3 in the upper axils, sessile or on pedicels to 4 mm, the petaliferous ones 6-7 mm, mingled with the apetalous ones; cal-tube 1.5-2 mm, its lobes subequal, oblong, reticulate, about as long as the tube; fr obovate, acute, scarcely reticulate, 3-4 mm; 2n=22. Fields and upland woods, mostly in dry soil; N.J. and Pa. to Ind. and Kans., s. to the Gulf; native of e. Asia. July, Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.