Leaf blades pale green abaxially, bright green adaxially, glabrous or with scattered, stipitate-glandular trichomes abaxially, usually not puberulent. Flowers: calyx puberulent and densely stipitate-glandular; corolla gla-brous or slightly puberulent adaxially.

Flowering May-Jul. Open bogs, swamps, wet areas; 0-800 m; N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Conn., Del., Maine, Md., Mass., Mich., N.H., N.J., N.Y., N.C., Pa., R.I., Vt., Va., W.Va.; introduced in n Europe.

Variety angustifolia is well known as a weed in plantations of commercial shrubs such as blueberries and of timber trees. It is difficult and sometimes costly to control in the blueberry fields and it is on the Canadian weed list (I. V. Hall et al. 1973; A. A. Ismail and D. E. Yarborough 1981). Variety angustifolia has allelopathic effects on black spruce (Picea mariana) seedlings, and has a competitive advantage over them. It may have the same effects on balsam fir (Abies balsamea) or at least play a role in reducing the growth of that tree (A. U. Mallik 1987, 1993; Mallik and P. F. Newton 1988; E. B. Peterson 1965; I. D. Thompson and Mallik 1989; H. Zhu and Mallik 1994).