Herbs stoloniferous. Stems erect, 40-130 cm, glabrous or subglabrous, striate. Leaves sessile or subsessile, ovate-oblong to oblong-lanceolate, 3-7 × 1-2 cm, base broadly cuneate to rounded, margin irregularly serrate, apex acute. Verticillasters in cylindric terminal spikes 4-10 cm, spikes interrupted at base; bracteoles linear, 5-8 mm. Pedicel ca. 2 mm. Calyx campanulate, ca. 2 mm, glandular, obscurely 5-veined; teeth triangular-lanceolate, ca. 1 mm. Corolla purplish, ca. 4 mm, glabrous, tube ca. 2 mm; lobes subequal, apex emarginate. Ovary brown, glabrous. Fl. Jul-Sep.
Herbs rhizomatous. Stems erect, 30-60 cm, purplish, glabrous. Leaves sessile or subsessile, ovate to ovate-lanceolate, 2-3 × 1.2-2 cm, papery, base rounded to shallow cordate, margin serrate, apex acute. Verticillasters in terminal spikes 2.5-3 × ca. 1 cm, continuous or ± interrupted at base; bracts linear-lanceolate, slightly longer than calyx. Pedicel ca. 1 mm. Calyx campanulate, ca. 1.5 mm, subglabrous, glandular, obscurely 5-veined; teeth triangular-lanceolate, ca. 0.1 mm, ciliate. Corolla purplish, ca. 3.5 mm, glabrous, tube ca. 2 mm; lobes subequal, apex emarginate. Ovary brown, glabrous. Nutlets brown, triquetrous, ovoid, ca. 0.7 mm, sparsely glandular.
Among the various Mentha spp. (mints) and their hybrids, Spearmint makes one of the better-flavored mint teas. Spearmint flavoring is also used in chewing gum and other products; it has significant economic importance. Spearmint has been widely cultivated since ancient times, and was introduced to the British Isles by the Romans. Distinguishing the various mints and their hybrids is often rather difficult. Spearmint can be identified by its hairless stems and leaves, the lack of petioles on its leaves, the wrinkled appearance of its leaves, the pleasant mint fragrance of its leaves, and its terminal spikes of flowers. Other mints tend to be more hairy, their leaves usually have petioles and they are less wrinkled in appearance, their leaves may not have a pleasant mint fragrance, or their flowers may occur in axillary whorls above the leaves.