1 Flowers in axillary verticils subtended by ordinary foliage leaves, and separated by internodes of ordinary length.

..2 Calyx glabrous throughout, or pubescent toward the tips only; calyx 2-3.5 mm long; plants usually sterile; fresh plant usually with spearmint odor or flavor

..2 Calyx pubescent throughout its length; calyx 1.5-2.5 mm long; plants usually fertile; fresh plant usually with a rather unpleasant odor or flavor.

....3 Leaves subtending the inflorescence mostly broadly rounded at the base; leaves of the inflorescence relatively narrow; [alien]

....3 Leaves subtending the inflorescence mostly cuneate at the base; leaves of the inflorescence relatively broad; [native, though often in weedy situations]

1 Flowers in terminal spikes or heads, the subtending leaves absent or distinctly smaller than the foliage leaves.

......4 Inflorescence a terminal globose to ovoid head of 1-3 verticils.

........5 Pedicels, calyx, and leaves pubescent; plants usually fertile

........5 Pedicels and clayx glabrous, leaves glabrous or nearly so; plants usually sterile

......4 Inflorescence a spike of several to many verticils.

..........6 Bracteal leaves much longer than the flowers, resembling the foliage leaves, but smaller or narrower

..........6 Bracteal leaves linear to lanceolate, little surpassing the flowers.

............ 7 Calyx tube glabrous; leaves glabrous, or with scattered hairs on the lower surface.

............ ..8 Petioles of the main leaves 4-15 mm long; spikes stout; plants sterile; fresh plant with peppermint odor or flavor

............ 7 Calyx tube pubescent; leaves moderately to densely hairy on the lower surface.

............ ....9 Leaves lanceolate to oblong-lanceolate, > 3× as long as wide.

............ ......10 Hairs of the leaf undersurface unbranched; leaves widest near the middle, slightly rugose; fertile anthers 0.28-0.38 mm long; fresh plant with musty flavor or odor

............ ....9 Leaves oblong to ovate, 1-3× as long as wide.

............ ........11 Leaves generally 1-2× as long as wide, ovate-orbicular, broadly rounded to subcordate at the base, obtuse at the apex; leaf serrations rounded and often turned downward (thus appearing crenate); leaf surface strongly rugose, with scattered dendritic hairs below; fresh plant with sickly or sweet flavor or odor

............ ........11 Leaves generally 1-3× as long as wide, ovate to oblong, broadly cuneate to rounded at the base, acute at the apex; leaf serrations sharp; leaf surface moderately rugose; fresh plant with spearmint odor.

............ ..........12 Leaves generally oblong, with nearly parallel sides and a broadly rounded base; flowers consistently with 4 fertile anthers

............ ..........12 Leaves generally ovate, infrequently oblong; flowers typically with all or mostly sterile anthers