Labiatae, the Mint Family
Herbs with opposite leaves, square stems, and usually aromatic odor; flowers irregular, with united petals, or almost regular; stamens 2 or 4, attached to the tube of the corolla; ovary deeply 4-lobed, with a single style.
| 1a. Stamens 2 — 2. | |
| 1b. Stamens 4 — 15. | |
| 2a. Corolla regular or nearly so; flowers white, in dense axillary clusters; plants usually of wet grounds (2-8 dm. high; summer and autumn) — 3. | |
| 2b. Corolla distinctly irregular and more or less 2-lipped — 7. | |
| 3a. Calyx-teeth short, triangular, acute or obtuse (Bugle Weed) — 4. | |
| 3b. Calyx-teeth narrow, acuminate or cuspidate (Water Hoarhound) — 5. | |
| 4a. Stems and stolons bearing tubers | Bugle Weed, Lycopus uniflorus. |
| 4b. Stems and stolons not bearing tubers | Bugle Weed, Lycopus virginicus. |
| 5a. Leaves serrate; calyx-teeth sharp-pointed — 6. | |
| 5b. Leaves coarsely incised; calyx-teeth awn-tipped | Water Hoarhound, Lycopus americanus. |
| 6a. Corolla twice as long as the calyx; leaves narrowed at the base | Water Hoarhound, Lycopus rubellus. |
| 6b. Corolla barely longer than the calyx; leaves sessile or nearly so | Water Hoarhound, Lycopus lucidus var. americanus. |
| 7a. Corolla blue, 3-4 mm. long; flowers in loose axillary clusters (1-4 dm. high; summer) (Pennyroyal) — 8. | |
| 7b. Corolla 8-40 mm. long — 9. | |
| 8a. Leaves serrate | Pennyroyal, Hedeoma pulegioides. |
| 8b. Leaves linear, entire | Pennyroyal, Hedeoma hispida. |
| 9a. Lower lobe of the corolla fringed, very much longer than the upper (5-15 dm. high; corolla pale-yellow; late summer) | Horse Balm, Collinsonia canadensis. |
| 9b. Lower lobe of the corolla nearly or quite as long as the upper and not fringed — 10. | |
| 10a. Calyx narrowly tubular; its teeth about equal in size (5-10 dm. high; flowers in dense terminal heads, in summer) — 11. | |
| 10b. Calyx campanulate, 2 of its teeth different in size from the other 3 (4-8 dm. high; flowers pink-purple, in terminal clusters in summer) — 14. | |
| 11a. Corolla scarlet | Oswego Tea, Monarda didyma. |
| 11b. Corolla bright crimson or rose-red | Wild Bergamot, Monarda fistulosa var. rubra. |
| 11c. Corolla white, pink, pale-purple, or yellowish — 12. | |
| 12a. Flower-clusters all terminal — 13. | |
| 12b. Flower-clusters both terminal and axillary | Horse Mint, Monarda punctata. |
| 13a. Leaves and stem with soft spreading pubescence | Wild Bergamot, Monarda fistulosa. |
| 13b. Leaves and stem grayish with fine appressed pubescence | Wild Bergamot, Monarda mollis. |
| 14a. Upper calyx-teeth about 3 times as long as the lower | Blephilia, Blephilia hirsuta. |
| 14b. Upper calyx-teeth but little longer than the lower | Blephilia, Blephilia ciliata. |
| 15a. Calyx with a distinct protuberance on the back of the upper side (Skullcap) — 16. | |
| 15b. Calyx without a distinct protuberance — 20. | |
| 16a. Corolla 5-8 mm. long; flowers in axillary racemes (3-8 dm. high; flowers blue, in summer) | Mad-dog Skullcap, Scutellaria lateriflora. |
| 16b. Corolla 6-10 mm. long; flowers axillary, solitary (1-3 dm. high; flowers violet, early summer) | Skullcap, Scutellaria parvula. |
| 16c. Corolla 12-30 mm. long; flowers axillary or in terminal racemes (4-8 dm. high; flowers blue, summer) — 17. | |
| 17a. Stem-leaves cordate | Skullcap, Scutellaria versicolor. |
| 17b. Stem-leaves not distinctly cordate — 18. | |
| 18a. Stem-leaves sessile or nearly so; plant of swamps and river-banks | Skullcap, Scutellaria galericulata. |
| 18b. Stem-leaves with petioles 1 cm. or more long; plants of dry or moist woods — 19. | |
| 19a. Stem glandular-pubescent toward the summit; corolla 16 mm. long or less | Skullcap, Scutellaria pilosa. |
| 19b. Stem not glandular; corolla 20 mm. long | Skullcap, Scutellaria incana. |
| 20a. Calyx-teeth 5, all equal or nearly so at the time of flowering — 28. | |
| 20b. Calyx-teeth 5, one of them different in size and shape from the other four (2-6 dm. high; flowers light blue, summer) | Dragon Head, Dracocephalum parviflorum. |
| 20c. Calyx-teeth 5, two of them different in size and shape from the other three — 21. | |
| 20d. Calyx-teeth 10, subulate (woolly plant 4-10 dm. high, with whitish flowers in axillary clusters in summer) | Hoarhound, Marrubium vulgare. |
| 21a. Corolla deeply split on the upper side and the stamens protruding; upper lip of the calyx much shorter than the lower (5-10 dm. high; flowers pink-purple, in terminal spikes, summer) (Wood Sage) — 22. | |
| 21b. Corolla not deeply split on the upper side — 23. | |
| 22a. Calyx canescent | Wood Sage, Teucrium canadense. |
| 22b. Calyx villous | Wood Sage, Teucrium occidentale. |
| 23a. Flowers in dense terminal head-like spikes, none axillary (1-5 dm. high; flowers pink-purple or blue, in summer) | Self-heal, Prunella vulgaris. |
| 23b. Some or all of the flowers in axillary clusters — 24. | |
| 24a. Leaves linear, entire (1-4 dm. high; flowers purple, summer) — 25. | |
| 24b. Leaves oblong to ovate (summer) — 26. | |
| 25a. Pedicels shorter than the calyx | Summer Savory, Satureja hortensis. |
| 25b. Pedicels much longer than the calyx | Calamint, Satureja glabra. |
| 26a. Leaves 1 cm. long or less, entire (stems growing in mats, 1-3 dm. long; flowers purple, in summer) | Wild Thyme, Thymus serpyllum. |
| 26b. Leaves dentate (flowers purple, summer) — 27. | |
| 27a. Flowers subtended by bracts as long as the calyx (2-5 dm. high) | Basil, Satureja vulgaris. |
| 27b. Flowers with minute bracts or none (1-3 dm. high) | Basil-thyme, Satureja acinos. |
| 28a. Corolla 2-lipped or nearly regular, the upper lip flattened, not conspicuously arched over the stamens — 29. | |
| 28b. Corolla conspicuously 2-lipped, the stamens ascending under the concave upper lip — 42. | |
| 29a. Flowers in dense terminal spikes; corolla 2-lipped (8-15 dm. high; summer) — 30. | |
| 29b. Flowers peduncled, 1-4 in the axils of linear leaves — 25b. | |
| 29c. Flowers in many-flowered whorls, which are axillary or terminal, or aggregated into terminal spikes or racemes — 31. | |
| 30a. Corolla yellowish | Giant Hyssop, Agastache nepetoides. |
| 30b. Corolla purplish | Giant Hyssop, Agastache scrophulariaefolius. |
| 31a. Corolla distinctly irregular, the lower lip longer than the upper — 32. | |
| 31b. Corolla almost regular, the lobes nearly uniform in size — 35. | |
| 32a. Stem-leaves sessile or very nearly so (flowers blue) — 33. | |
| 32b. Stem-leaves long-petioled — 34. | |
| 33a. Leaves linear-oblong, acute at both ends (3-8 dm. high; summer) | Hyssop, Hyssopus officinalis. |
| 33b. Leaves oblong to ovate, rounded at the ends (2-4 dm. high; late spring) | Bugle, Ajuga reptans. |
| 34a. Leaves ovate to oblong, acute; flowers pink, white, or pale purple (6-15 dm. high; summer) | Catnip, Nepeta cataria. |
| 34b. Leaves nearly circular or kidney-shape; flowers blue (creeping; flowers in spring and summer) | Ground Ivy, Nepeta hederacea. |
| 35a. Flowers in terminal spikes, or the lower axillary (3-8 dm. high; flowers pink-purple or white, summer) (Mint) — 36. | |
| 35b. Flowers all in axillary whorls (flowers pink-purple or white, summer) (Mint) — 38. | |
| 35c. Flowers in terminal capitate corymbed clusters (4-8 dm. high; flowers white or dotted with purple, summer) (Mountain Mint) — 41. | |
| 36a. Leaves sessile or with very short petiole | Spearmint, Mentha spicata. |
| 36b. Leaves with manifest petioles — 37. | |
| 37a. Principal leaves less than half as broad as long | Peppermint, Mentha piperita. |
| 37b. Principal leaves more than half as broad as long | Bergamot Mint, Mentha citrata. |
| 38a. Stem glabrous; leaves ovate to obovate (4-8 dm. high) | Downy Mint, Mentha gentilis. |
| 38b. Stem pubescent, at least on the angles (1-6 dm. high) — 39. | |
| 39a. Principal leaves distinctly petioled and somewhat rounded at base | Wild Mint, Mentha arvensis. |
| 39b. Leaves tapering to the base — 40. | |
| 40a. Leaves and stem pubescent | Wild Mint, Mentha arvensis var. canadensis. |
| 40b. Leaves glabrous; stem pubescent on the angles only | Wild Mint, Mentha arvensis var. glabrata. |
| 41a. Leaves linear; calyx-teeth awl-shape | Mountain Mint, Pycnanthemum flexuosum. |
| 41b. Leaves narrowly lanceolate; calyx-teeth triangular-ovate | Mountain Mint, Pycnanthemum virginianum. |
| 42a. Stems decumbent to diffuse; leaves cordate to nearly circular (stems 2-5 dm. long or high; flowers in spring and summer) (Dead Nettle) — 43. | |
| 42b. Stem erect; leaves palmately cleft; calyx-teeth spiny (6-15 dm. tall; flowers pink, in summer) | Motherwort, Leonurus cardiaca. |
| 42c. Stems erect or ascending; leaves ovate-lanceolate to linear (summer) — 45. | |
| 43a. Upper leaves closely sessile (flowers red-purple) | Dead Nettle, Lamium amplexicaule. |
| 43b. Leaves all petioled — 44. | |
| 44a. Flowers red or purple | Dead Nettle, Lamium maculatum. |
| 44b. Flowers white | Dead Nettle, Lamium album. |
| 45a. Flowers 2-2.5 cm. long, in loose terminal spikes (5-10 dm. tall; flowers rose-color) | False Dragon Head, Physostegia virginiana. |
| 45b. Flowers 1-2 cm. long, in axillary and terminal spiked whorls — 46. | |
| 46a. Calyx-teeth spiny pointed (flowers pink or pale-purple) (Hemp Nettle) — 47. | |
| 46b. Calyx-teeth acute to awl-shape, but not spiny (3-10 dm. high; flowers pale-purple) (Hedge Nettle) — 48. | |
| 47a. Leaves ovate (3-8 dm. high) | Hemp Nettle, Galeopsis tetrahit. |
| 47b. Leaves linear to lanceolate (1-4 dm. high) | Hemp Nettle, Galeopsis ladanum. |
| 48a. Leaves glabrous — 49. | |
| 48b. Leaves distinctly pubescent — 50. | |
| 49a. Leaves ovate-lanceolate, serrate | Hedge Nettle, Stachys tenuifolia. |
| 49b. Leaves linear-oblong, entire or nearly so | Hedge Nettle, Stachys hyssopifolia. |
| 50a. Stem pubescent on the angles alone; leaves petioled | Hedge Nettle, Stachys tenuifolia var. aspera. |
| 50b. Stem pubescent on both sides and angles; leaves nearly sessile — 51. | |
| 51a. Leaves oblong or oblong-lanceolate, more than 1 cm. wide | Hedge Nettle, Stachys palustris. |
| 51b. Leaves linear-lanceolate, 1 cm. wide or less | Hedge Nettle, Stachys arenicola. |