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Genus Mentha Family Lamiaceae

Description: Perennial herb; branches 4-angular; hairs simple or rarely branched; glands sessile.

Leaves opposite, simple, margins toothed or entire; petiolate or sessile.

Inflorescence consisting of clusters of flowers in upper leaf axils or flowers arranged in terminal spike-like clusters. Sepals ± regularly fused, forming 5 equal or ± equal lobes. Corolla slightly 2-lipped or 4-lobed, then lower lip with 3 ± equal lobes and upper lobe truncate, emarginate or 2-lobed. Stamens 4, fertile, inserted below the throat of the corolla tube; filaments erect; anthers with 2 fertile loculi, not diverging.

Mericarps not keeled.

Distribution and occurrence: World: c. 25 species, temperate Northern Hemisphere & southern Africa, Australia. Australia: 10 species (4 species endemic, 6 species naturalized), all States.

Text by B. J. Conn
Taxon concept:

 Key to the species 
1Clusters of flowers in upper leaf axils, with branch visible between the clusters; calyx 13-veined (except M. pulegium 10-veined)2
Flower clusters terminal, forming a spike-like inflorescence, clusters subtended by narrow bracts, not subtended by leaves, with branch frequently not visible between the clusters; calyx 10-veined6
2Calyx lobes villous on inner surface; clusters few-flowered. (Mentha satureioides group)3
Calyx lobes with short more or less spreading hairs on inner surface, not villous; clusters few- to many-flowered
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3Branches almost glabrous; calyx glabrous on outer surface; flowers in 3-flowered clusters per leaf axil; leaves narrow-elliptic to linear-elliptic, 0.5–3.5 cm long, 0.2–0.7 cm wide; margins entireMentha satureioides
Branches and calyx hairy; flowers in 3–8-flowered clusters per leaf axil; leaves ovate, often angular-ovate, rarely narrow-ovate or elliptic, 0.6–2 cm long, 0.4–1.2 cm wide; margins entire or sometimes with distant shallow teeth
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Mentha diemenica
4Flowers 2–6, rarely more per leaf axilMentha laxiflora
Flowers crowded in dense clusters, at least 10 flowers per leaf axil
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5Leaves narrow-ovate, 1.2–6 cm long, 8–20 mm wide, margins with 2–7 teeth, apex acute; calyx 13-veined; corolla white or pinkMentha australis
Leaves obovate, elliptic to more or less circular, 0.6–3 cm long, 4–20 mm wide, margins entire or with small blunt teeth, apex obtuse or rounded; calyx 10-veined; corolla usually pale-mauve to lilac
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Mentha pulegium
6Branches and lower surface of leaves densely hairy, with branched and long simple hairsMentha x rotundifolia
Branches and leaves glabrous or sparsely hairy, especially on the veins
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7Basal leaves sessile; plants producing fruit; calyx lobes about half the length of calyxMentha spicata
Basal leaves petiolate; plants not producing fruit; calyx lobes a third the length of calyx
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Mentha x piperita

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