American Corn Mint, Corn Mint, Field Mint, Wild Mint: Mentha canadensis (Synonyms: Mentha arvensis, Mentha arvensis ssp. borealis, Mentha arvensis ssp. haplocalyx, Mentha arvensis var. arvensis, Mentha arvensis var. canadensis, Mentha arvensis var. glabrata, Mentha arvensis var. lanata, Mentha arvensis var. sativa, Mentha arvensis var. villosa, Mentha gentilis, Mentha glabrior, Mentha penardii) - Verticils of flowers are axillary, all subtended by large leaves and separated by conspicuous internodes. Leaves larger, 2-8 cm long with several pairs of lateral veins. Leaves of the inflorescence noticeably longer than the verticils and spreading.
Peppermint: Mentha xpiperita (Synonyms: Mentha aquatica x Mentha spicata, Mentha aquatica var. crispa, Mentha crispa, Mentha dumetorum, Mentha piperita) - Verticils of flowers crowded into terminal, often elongated, inconspicuously leafy bracteate inflorescences at the tip of the stem or tips of the lateral branches. Leaves noticeably petiolate, the petioles typically longer than 4 mm. Spikes stout, generally 1-2 cm thick in bloom.
Pennyroyal: Mentha pulegium - Verticils of flowers are axillary and separated by conspicuous internodes. Leaves small, up to 2 cm long with the blades with 2-3 pairs of lateral veins. Leaves of the inflorescence about equal to (to much smaller than) the verticils in size and deflexed.
Spearmint: Mentha spicata (Synonyms: Mentha cordifolia, Mentha longifolia, Mentha longifolia var. mollissima, Mentha longifolia var. undulata, Mentha spicata var. longifolia, Mentha spicata var. spicata, Mentha sylvestris, Mentha viridis) - Verticils of flowers crowded into terminal, often elongated, inconspicuously leafy bracteate inflorescences at the tip of the stem or tips of the lateral branches. Leaves sessile to subsessile, any petiole present not greater than 3 mm long. Spikes slender, generally 0.5-1 cm thick in bloom.
Applemint, Apple-scented Mint, Round-leaved Mint: Mentha suaveolens (Synonym: Mentha rotundifolia) -