Coarse, erect annual to 2 m; stems hexagonal; lvs mostly or all whorled or opposite, lanceolate to lance-ovate, acuminate, sharply serrate; racemes ascending on long peduncles, few-fld; fls purple or blue, varying to white, 3 cm; 2n=18, 20. Native of the Himalayan region, becoming established as an escape from cult. in the ne. part of our range. Summer. (I. roylei)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.