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 piperita L. Sp. Pl. 576. 1753.
Perennial by subterranean suckers; stems glabrous, mostly erect, branched, 1°-3° high. Leaves lanceolate, petioled, dark green, acute at the apex, rounded or narrowed at the base, rather firm, sharply serrate, glabrous on both sides, or pubescent on the veins beneath, the larger 1 1/2'-3' long, 1'-1 1/2' wide; whorls of flowers in terminal dense or interrupted spikes, which are thick and obtuse, and become 1'-3' long in fruit, the middle one at length overtopped by the lateral ones; bracts lanceolate, acuminate, not longer than the flowers, or the lower occasionally folia-ceous; calyx tubular-campanulate, glabrous below, its teeth subulate, ciliate, one-half as long as the tube or more; corolla glabrous; style occasionally 3-cleft.
Mentha citrata Ehrh. Beitr. 7: 150. 1792.
Perennial by leafy stolons, glabrous throughout; stem weak, branched, decumbent or ascending, 1°-2° long. Leaves petioled, thin, ovate or ovate-orbicular, obtuse or the upper acute at the apex, rounded or subcordate at the base, sharply serrate with low teeth, the larger about 2' long, 1'-1 1/2' wide; whorls of flowers in terminal dense thick obtuse spikes, and commonly also in the uppermost axils; spikes scarcely more than 1' long in fruit; calyx glabrous, its teeth subulate, one-half as long as the tube, or longer; corolla glabrous.
In wet soil, Connecticut to New York, Ohio, Michigan and Missouri. Naturalized from Europe. Also in Bermuda and Porto Rico. July-Sept.
Mentha spicata var. longifolia L. Sp. Pl. 576. 1753. Mentha longifolia Huds. Fl. Angl. 221. 1762. Mentha sylvestris L. Sp. Pl. Ed. 2, 804. 1763.
Perennial by suckers, canescent or puberulent nearly all over; stems mostly erect, branched, or simple, 1°-2 1/2° high. Leaves lanceolate, ovate-lanceolate, or oblong-lanceolate, sessile, or very short-petioled, acute at the apex, usually rounded at the base, sharply serrate, 1'-3' long, 1/2'-1 1/4' wide, sometimes glabrous above; whorls of flowers in terminal narrow dense or interrupted acute spikes, which become 2'-5' long in fruit; bracts lanceolate-subulate, the lower equalling or longer than the flowers; calyx tomentose or canescent, its teeth subulate, one-half as long as the campanu-late tube; corolla puberulent.