| 1. Internodes between upper inflorescences evident, generally > 1 cm; inflorescences subtended by ovate, elliptic, or lanceolate leaves |
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| 2. Leaves subtending inflorescence 1.53 cm, > inflorescence diam, spreading, generally serrate |
| M. arvensis |
| 2' Leaves subtending inflorescences generally < 1 cm, generally < inflorescence diam, reflexed, generally entire |
| M. pulegium |
| 1' Internodes between upper inflorescences generally inconspicuous, generally < 6 mm; inflorescence generally subtended by linear, lanceolate, or awl-like bracts |
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| 3. Cauline leaves petioled, petiole 38 mm; inflorescences generally > 10 mm diam, head-like, lower 23 separated by short internodes |
| M. ×piperita |
| 3' Cauline leaves subsessile or sessile, petiole < 1 mm; inflorescences generally < 5 mm diam, collectively spike-like |
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| 4. Cauline leaf base obtuse or rounded, tip acute or acuminate, lower surface generally glabrous or white-soft-hairy |
| M. spicata var. spicata |
| 4' Cauline leaf base slightly lobed, tip rounded, lower surface stellate-tomentose |
| M. suaveolens
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