Diffusely branched, mat-forming perennial, rooting at the nodes; stems woody at base; fl stems ±erect, to 1 dm, hairy all around; lvs linear to subrotund, in our wild forms commonly elliptic to oblong-ovate or oblong-obovate, 5-10 mm, short-petioled; fls aggregated into a continuous or interrupted terminal "spike" 1-4(-15) cm; cal 3-4 mm; cor purple, 4-6 mm; 2n=24+. Native of Europe, commonly cult. and escaped into upland woods and fields; N.S. to w. N.Y. and Ont., s. to W.Va. and N.C. June-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.