Mentha pulegium L., Lamiaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

Chinese: chun e bo he

English: European pennyroyal, pennyroyal, peppermint

French: menthe pouliot, pouliot

Spanish: menta, poleo

Habit:  herb

Description:  "Aromatic, tomentose perennial herbs; stems procumbent to ascending, 1-4 dm long.  Leaves narrowly ovate to narrowly elliptic, 8-30 mm long, 0.4-12 mm wide, pubescent at least on lower surface, margins subentire or with up to 6 teeth on each side, base attenuate, sessile or subsessile.  Flowers in well-spaced verticillasters in the leaf axils; calyx (2-) 2.5-3 mm long, the teeth ciliate, lower ones subulate, upper ones slightly shorter and wider; corolla lilac, (4-) 4.5-6 mm long; stamens exserted beyond to included in corolla tube.  Nutlets pale brown, ca. 0.7-0.8 mm long"  (Wagner et al., 1999; p. 807).

Habitat/ecology:  "Grassland, riparian habitats, freshwater wetlands, alluvial plains.  A highly variable species with regard to growth habit and leaf shape.  Several varieties have been described in the native range where it hybridizes with several congeners.  The plant forms dense stands that crowd out native vegetation and reduce species richness.  Damaged plants easily resprout"  (Weber, 2003; p. 266).

In Hawai‘i, "cultivated and escaping from gardens, usually in damp areas"  (Wagner et al., 1999; p. 807).  "In Chile this species grows in the following environmental conditions:  Low altitude, interior valleys; coastal mountains, 500-2000 m; coastal areas, 0-500 m.  Humid areas, with almost constant rainfall, short dry periods are possible (generally not longer than 1 month); somewhat dry areas where the drought may last 3-5 months, precipitations of 400-800 mm. are concentrated in winter.  Fully exposed to the sun, level areas or slopes facing north"  (Chileflora).

Propagation:  Seed.  "It is a prolific seed producer, and seeds are dispersed by water and animals.  Seedlings can emerge and establish under water, enabling the plant to invade flooded areas.  It accumulates a soil seed bank"  (Weber, 2003; p. 266).

Native range:  "Native to Europe, widely naturalized" (Wagner et al., 1999; p. 807).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Chile (offshore islands) Juan Fernández Islands	Isla Más a Tierra (Robinson Crusoe Island)	introduced invasive	Atkinson, Rachel/Sawyer, John (2011)
Chile (offshore islands) Juan Fernández Islands	Isla Más a Tierra (Robinson Crusoe Island)	introduced invasive	Danton, Philippe/Perrier, Christophe/Martinez Reyes, Guido (2006) (p. 555)
Chile (offshore islands) Juan Fernández Islands	Isla Más Afuera (Alejandro Selkirk Island)	introduced	Skottsberg, Carl (1953) (p. 223)
Chile (offshore islands) Juan Fernández Islands	Isla Más Afuera (Alejandro Selkirk Island)	introduced invasive	Atkinson, Rachel/Sawyer, John (2011)
Chile (offshore islands) Juan Fernández Islands	Isla Más Afuera (Alejandro Selkirk Island)	introduced invasive	Danton, Philippe/Perrier, Christophe/Martinez Reyes, Guido (2006) (p. 555)
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island		Bishop Museum (U.S.A. Hawaii. Honolulu.) (1948) (voucher ID: BISH 53279) Taxon name on voucher: Mentha pulegium L.
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive cultivated	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 807) Voucher cited: Forbes 2633.M (BISH) Cultivated and escaping from gardens.
New Caledonia New Caledonia Archipelago	Île Grande Terre	introduced cultivated	MacKee, H. S. (1994) (p. 69) Voucher cited: MacKee 34795

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	Australia (continental)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Chile (continental) Chile	Chile (Republic of)	introduced	Skottsberg, Carl (1953) (p. 223)
Chile (continental) Chile	Chile (Republic of)	introduced invasive	Belov, Michail (2011)
China China	China (People's Republic of)	introduced cultivated	Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2011) Beijing Shi, Nanjing Shi, and other cities.
Japan Japan	Japan (country)	introduced	Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 188)
New Zealand New Zealand	New Zealand (country)	introduced invasive cultivated	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 780) "Common to abundant in wet pastures, by rivers and lakesides, also in drier places, including bare lava and backs of sandy beaches".

Control: 

Physical:  "Single plants and small patches are hand pulled or dug out.  Roots and stolons must be removed to prevent regrowth.  Follow-up programs are necessary to treat regrowth and seedlings".

Chemical:  "Seedlings can be controlled with 2,4-D, established plants with glyphosate, metsulfuron-methyl, or triclopyr plus picloram"  (Weber, 2003; p. 266).

Additional information:
Photos and other information from Chileflora.

Additional online information about Mentha pulegium is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Mentha pulegium as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Mentha pulegium may be available from the Germplasm Resources Information Network (GRIN).

References:

Atkinson, Rachel/Sawyer, John. 2011. Naturalized species in the Juan Fernández Archipelago, Chile. Unpublished spreadsheet.

Belov, Michail. 2011. Chileflora (online resource).

Bishop Museum (U.S.A. Hawaii. Honolulu.). 1948. Voucher specimen #BISH53279(Greenwell, A.B.H. 19240).

Danton, Philippe/Perrier, Christophe/Martinez Reyes, Guido. 2006. Nouveau catalogue de la flore vaculaire de l'archipel Juan Fernández (Chile) [Nuevo catálogo de la flora vacular del Archipélago Juan Fernández (Chile)]. Acta Bot. Gallica 153(4):399-587.

MacKee, H. S. 1994. Catalogue des plantes introduites et cultivées en Nouvelle-Calédonie. Muséum National d'Histoire Naturelle, Paris, 164 p.

Mito, Toshikazu/Uesugi, Tetsuro. 2004. Invasive alien species in Japan: the status quo and the new regulation for prevention of their adverse effects. Global Environmental Research 8(2)/2004: 171-191.

Skottsberg, Carl. 1953. The natural history of Juan Fernandez and Easter Island. Vol. II, Botany. Almqvist &l; Wiksells, Uppsala. 960 pp.

Staples, George W./Herbst, Derral/Imada, Clyde T. 2000. Survey of invasive or potentially invasive cultivated plants in Hawai‘i. Bishop Museum Occasional Papers No. 65. 35 pp.

U. S. Government. 2011. Integrated Taxonomic Information System (ITIS) (on-line resource).

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. 1999. Manual of the flowering plants of Hawaii. Revised edition. Bernice P. Bishop Museum special publication. University of Hawai‘i Press/Bishop Museum Press, Honolulu. 1919 pp. (two volumes).

Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. 1988. Flora of New Zealand, Volume IV: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch. 1365 pp.

Weber, Ewald. 2003. Invasive plants of the World. CABI Publishing, CAB International, Wallingford, UK. 548 pp.

Zhengyi, Wu/Raven, Peter H./Deyuan, Hong. 2011. Flora of China (online resource).