This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Mentha spicata var. rotundifolia L. Sp. Pl. 576. 1753.
Mentha rotundifolia Huds. Fl. Angl. 221. 1762.
Perennial by leafy stolons, canescent or tomentose-puberulent, somewhat viscid; stems ascending or erect, simple or branched, usually slender, 1 1/2°-2 1/2° high. Leaves elliptic, or ovate-oblong, short-petioled, or sessile and somewhat clasping by the subcordate or rounded base, obtuse at the apex, crenate-serrate with low teeth, 1'-2' long, 9"-15" wide, more or less rugose-reticulated beneath; whorls of flowers in terminal dense or interrupted spikes which elongate to 2'-4' in fruit; bracts lanceolate, acuminate, commonly shorter than the flowers; calyx-teeth setaceous, usually about one-half as long as the tube; corolla puberulent.
Mentha alopecuroides Hull. Brit. Fl. 221. 1799.
Perennial by suckers, white-woolly; stem stout, leafy, erect or ascending, simple or branched, 1 1/2°-3° high. Leaves broadly oval, sessile, or partly clasping by a subcordate or rarely rounded base, obtuse at the apex, sharply and rather coarsely serrate, pinnately-veined, the lower 2-3' long, 1 1/2-2' wide; spikes rather thick, dense, stout, obtuse, 2-3' long in fruit; bracts lanceolate, shorter than the flowers; calyx-teeth setaceous, one-half as long as the campanulate tube, or more; corolla pubescent.
Along roadsides, Connecticut to New Jersey, Pennsylvania, Wisconsin and Missouri. Naturalized . from Europe. July-Oct.
Mentha aquatica L. Sp. Pl. 576. 1753.
Perennial by suckers, hirsute or pubescent, rarely glabrate; stem stout, erect, leafy, usually branched, 1 1/2°-2 1/20 high, its hairs reflexed. Leaves broadly ovate, petioled, acute, subacute or the lower obtuse at the apex, rounded, subcordate or rarely narrowed at the base, sharply serrate, the larger 1 1/2'-3' long and nearly as wide; whorls of flowers in terminal dense short thick rounded spikes, and usually also in the upper axils; spikes seldom more than 1' long in fruit; bracts lanceolate, shorter than the flowers; calyx hirsute, its teeth lanceolate-subulate or triangular-lanceolate, one-third to one-half as long as the nearly cylindric tube; corolla sparingly pubescent.
In wet places, Nova Scotia to Pennsylvania and Georgia. Naturalized from Europe. Aug.-Oct.
Mentha crispa L. Sp. Pl. 576. 1753. Mentha aquatica var. crispa Benth. Lab. Gen. & Sp. 177. 1833.
Sparingly pilose-pubescent at least at the nodes, petioles and veins of the lower surfaces of the leaves; stem rather weak, usually much branched, 1 1/2°-3° long. Leaves distinctly petioled, or the uppermost sessile, ovate in outline, mostly acute at the apex, rounded, truncate or subcordate at the base, their margins crisped, wavy and incised, or the uppermost merely sharply serrate; whorls of. flowers in dense thick rounded terminal spikes, which become 1'-1 1/2' long in fruit; calyx sparingly pubescent or glabrous, its teeth subulate, more than one-half as long as the campanulate tube; corolla glabrous.
In swamps and roadside ditches, Connecticut to New Jersey and Pennsylvania. Balm-mint. Aug.-Oct.