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| 1 |
Calyx tubular or campanulate-tubular, slightly curved, 2-lipped; teeth of upper lip lanceolate-triangular, shorter than subulate teeth of lower lip; tube hairy at throat inside, closed in fruit, hirtellous outside, conspicuously veined; corolla saccate at throat in front |
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12 Mentha pulegium |
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Calyx broadly campanulate or funnelform-campanulate, straight, regular; teeth ± equal; tube glabrous at throat, spreading in fruit, obscurely veined, not hirtellous; corolla throat slightly dilated, not saccate. |
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(2) |
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| 2 (1) |
Verticillasters widely spaced, inserted in leaf axils, sometimes along entire stem; leaves longer than verticillasters; corolla throat hairy. |
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(3) |
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Verticillasters in leafless, terminal, capitate or spicate inflorescences, upper ones contiguous; floral leaves linear or nearly similar to stem leaves; corolla throat hairy or glabrous inside. |
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(4) |
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| 3 (2) |
Stems much branched, puberulent at apex and along angles at base; leaves 3-5(-7) cm, sparsely coarsely dentate-serrate; calyx teeth puberulent; stamens and style usually slightly exserted |
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1 Mentha canadensis |
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Stems unbranched or branched at apex, densely pubescent; leaves (2.5-)4-9 cm, irregularly shallow serrate; calyx teeth pilose; stamens and style usually much exserted |
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2 Mentha sachalinensis |
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| 4 (2) |
Verticillasters 1-3, in short, capitate, rarely elongated inflorescences; basal verticillasters sometimes remote from upper, axillary, with large floral leaves; calyx tubular; corolla hairy inside; nutlets glabrous |
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3 Mentha dahurica |
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Verticillasters in spicate continuous or interrupted inflorescences; floral leaves linear or similar to stem leaves, generally minute; calyx campanulate; corolla throat glabrous inside; nutlets apex hairy. |
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(5) |
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| 5 (4) |
Leaves crisped, ovate to ovate-lanceolate, incised-serrate; calyx teeth slightly close together |
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10 Mentha crispata |
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Leaves not crisped; calyx teeth not close together in fruit. |
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(6) |
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| 6 (5) |
Leaves glabrous or subglabrous, dark green or shiny green. |
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(7) |
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Leaves hairy at least abaxially. |
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(9) |
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| 7 (6) |
Adaxial stem leaves sessile or subsessile; inflorescences slender, 4-10 cm, interrupted; plants shiny green |
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9 Mentha spicata |
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Adaxial stem leaves petiolate; inflorescences robust, interrupted at base; plants dark green. |
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(8) |
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| 8 (7) |
Stem leaves lanceolate to ovate-lanceolate, apex acute; calyx teeth ciliate |
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7 Mentha X piperita |
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Stem leaves ovate to elliptic, apex obtuse; calyx teeth not ciliate |
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8 Mentha citrata |
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| 9 (6) |
All leaves sessile, corrugate, margin crenate or crenate-serrate |
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11 Mentha suaveolens |
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Lower leaves sometimes petiolate, leaves not corrugate when all sessile, not crenate or crenate-serrate. |
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(10) |
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| 10 (9) |
Plants densely gray tomentose, much branched |
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6 Mentha vagans |
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Plants not entirely densely gray tomentose, not much branched. |
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(11) |
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| 11 (10) |
Leaves mostly sessile, coarsely serrate-dentate, dark green or green and hairy, sometimes abaxially densely appressed tomentose-pubescent; inflorescence robust; pedicel tomentose-villous; calyx as long as corolla tube, spreading hairy, teeth as long as tube; corolla ca. 4 mm |
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4 Mentha longifolia |
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Leaves short petiolate or subsessile, remotely shallow unequal dentate, glaucous, finely minutely tomentose or crisped tomentose; inflorescences rather slender, sometimes interrupted; pedicel appressed pubescent; calyx shorter than corolla tube, appressed pubescent, teeth 3/4 as long as tube; corolla 4-5 mm |
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5 Mentha asiatica |
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