Lippia graveolens (PROSEA)
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Introduction |
Lippia graveolens Kunth
- Protologue: Nov. gen. sp. 2: 267 (1818).
- Family: Verbenaceae
- Chromosome number: 2n = unknown
Synonyms
- Lippia berlandieri J. Schauer (1847).
Vernacular names
- Mexican oregano, Mexican marjoram, Mexican wild sage (En).
- Marjolaine du Mexique, origan marjolaine (Fr)
- Philippines: oregano, karabo (Cebuano)
Origin and geographic distribution
Mexican oregano is native in the area extending from the southern United States to Nicaragua. It is cultivated in Central America.
Uses
Mexican oregano is an important spice in Mexico and Central America, where the fresh or dried leaves, as well as the flowers, are used as a culinary seasoning. It is particularly suited to flavour fish, sausages, tomato sauces and other dishes requiring a strong oregano flavour. In the United States, it is often employed in Mexican-style food (e.g. chili con carne) and in Italian-style food (e.g. pizza). A herbal tea can be made from the dried leaves. In the United States the regulatory status "generally recognized as safe” has been accorded to Mexican oregano (GRAS 2827).
The essential oil, obtained from the plant by steam distillation, has largely replaced the herb in the food industry. The oil is used to flavour relishes. Mexican oregano extract is applied as a flavour component in many food products and drinks. The maximum permitted level in food products such as condiments and milk products is about 0.3%.
In Mexico, leaf decoctions of Mexican oregano are credited with anti-diabetes properties, and are used against dysentery, as an intestinal antiseptic, a febrifuge and to regulate menstruation. If taken during pregnancy, they may cause abortion. A syrup from the leaves is used against coughs and colds.
Production and international trade
Mexican oregano is mainly produced and exported by Mexico. The annual oregano production in Mexico in the early 1990s was estimated at 3000 t, of which about 2000 t was exported to the United States, 600-800 t consumed locally, and the remainder exported to other smaller markets. The United States import price of Mexican oregano is usually only half to two-thirds of that of oregano (Origanum vulgare L.) from Greece.
Properties
The fresh plant contains per 100 g: water 69.2 g, protein 5.0 g, fat 1.5 g, carbohydrates 17.6 g, fibre 4.1 g, ash 2.6 g (Ca 649 mg, P 56 mg, Fe 5.32 mg), carotene 8.38 mg, thiamine 0.39 mg, riboflavin 0.04 mg, niacin 1.64 mg and ascorbic acid 62.0 mg.
The leaves of Mexican oregano have an intense oregano aroma and the flavour is stronger, sharper and more pungent than that of Origanum species. The essential-oil content is about 3-4%. The principal compounds of the essential oil are thymol (40-60%) and carvacrol (3-25%). Published analyses of the essential oil vary widely, both quantitatively and qualitatively. Thymol and carvacrol have strong fungicidal, anthelminthic and irritant properties. The aerial parts and roots of Mexican oregano also contain lapachenole, which is carcinogenic and may contribute to its antifertility activity.
Composition
Mexican oregano oil (from United States) (Source: Lawrence, 1996)
- 50.0% thymol
- 12.0% carvacrol
- 8.5% para-cymene
- 4.0% 1,8-cineole
- 3.5% γ-terpinene
- 3.0% terpinen-4-ol
- 1.8% terpinen-4-yl acetate
- 1.7% myrcene
- 1.2% δ-3-carene
- 1.1% α-terpinene
- 1.0% borneol
- 1.0% linalool
- 1.0% trans-p-menth-2-en-1-ol
- 1.0% α-pinene
- 0.9% α-terpineol
- 0.8% β-bisabolene
- 0.6% limonene
- 0.6% β-phellandrene
- 0.5% β-caryophyllene
- 0.5% ledene
- 0.5% methyl chavicol
- 0.5% methyl thymol
- 0.4% terpinolene
- 0.4% γ-gurjunene
- 0.3% α-phellandrene
- 0.3% γ-muurolene
- 0.3% trans-sabinene hydrate
- 0.3% thymyl acetate
- 0.2% cis-α-bisabolene
- 0.2% camphene
- 0.2% piperitone
- 0.2% α-thujene
- 0.2% 1-octenol-3
- 0.1% calamenene
- 0.1% α-copaene
- 0.1% cis-p-menth-2-en-1-ol
- 0.1% β-pinene
- 0.1% cis-sabinene hydrate
- 0.1% trans-α-bergamotene
- 0.1% δ-cadinene
- 0.1% γ-cadinene
- 0.1% p-cymen-8-ol
- 0.1% sabinene
- trace carveol
- trace 2-ethylfuran
- trace ethyl isobutyrate
- trace ethyl 2-methylbutyrate
- trace 2-methylbutanal
- trace 2-methylpropanal
- trace δ-terpineol
- trace umbellulone
- 99.2% total
Adulterations and substitutes
Mexican oregano shipments have been found adulterated with herbs such as sumac (Rhus coriaria L.), and all United States imports now have to be tested for its presence.
Various other Lippia species are harvested from the wild and are used as oregano in Mexico and Central America, and they are probably also incorporated into export materials. They include L. affinis J. Schauer, L. cardiostegia Benth., L. formosa T.S. Bandeg., L. fragrans Turcz., L. micromera J. Schauer, L. origanoides Kunth, L. palmeri S. Watson and L. umbellata Cav. Species from other genera are sometimes also called Mexican oregano and used similarly, e.g. Monarda fistulosa L. var. menthaefolia (Graham) Fernald, M. austromontana Epling and Poliomintha longiflora A. Gray.
Description
- Aromatic, slender shrub or small tree, up to 9 m tall. Branchlets slender, straggling, brittle, densely resinous-punctate, hairy, with flaky bark.
- Leaves opposite; petiole 2-20 mm long, appressed pubescent; blade oblong to ovate or elliptical, 1-7 cm × 0.5-3.5 cm, base rounded, margin regularly crenate with closely set blunt teeth, apex rounded or acute, upper and lower surface velvety hairy and resinous-glandular.
- Inflorescence a compact, nearly globose or cylindrical spike, 4-12 mm long, usually in groups of 4-6 in leaf axils; peduncle as long as the petiole; flowers fragrant, white to yellow, small, sessile in the axil of a bractlet; bractlets plainly 4-ranked, conduplicate-carinate, narrow lanceolate, 3-8 mm long, imbricate, connate at base, hirsute-tomentose, resinous-glandular.
- Calyx small, persistent, 3-6 mm long; corolla salverform, tube 3-6 mm long, limb spreading and 4-parted; stamens 4, didynamous, inserted at about the middle of the corolla tube; pistil with 2-celled ovary, short style and thickened stigma.
- Fruit small, dry, included in the calyx, dividing into 2 nutlets at maturity.
Growth and development
Mexican oregano usually flowers from July to September in Mexico. In areas where wild Mexican oregano is harvested regularly, plants are often not taller than 1 m.
Other botanical information
Several other Lippia species in addition to those mentioned under "Adulterations and substitutes” have uses for food and medicine. L. alba (Miller) N.E. Brown (anise verbena, licorice verbena) is a slow-growing shrub, native to temperate and tropical Central and South America. Its fresh leaves have an anise aroma reminiscent of lemongrass (Cymbopogon citratus (DC.) Stapf) and the herb is valued as a flavouring of soup, meats, fish and for making tea. It is grown as an essential-oil crop in Argentina and is widely cultivated elsewhere as a medicinal, aromatic and ornamental plant. L. dulcis Trévir. (synonym: Phyla scaberrima (Juss. ex Pers.) Moldenke), (Mexican lippia, sweet lippia), a perennial herb native to Central America, is used in Central America as a medicine against bronchial ailments. The essential oil contains the very sweet sesquiterpenoid hernandulcin, but the potential use for sweetening purposes is limited, because the main constituent of the oil is the toxic compound camphor. Camphor may also be responsible for the reputed abortifacient activity of Mexican lippia. L. micromera (Spanish thyme), a shrub native to South America, is used in the Caribbean as a culinary herb and medicinal plant. As is the case for Mexican oregano, there is no information on the cultivation or use of these Lippia species in South-East Asia.
Ecology
Mexican oregano is adapted to arid conditions and prefers full sun. It is susceptible to frost, especially under wet conditions. In its native habitat, Mexican oregano grows on rocky-clay roadsides, hills, bushy slopes and cliffs. For cultivation, well-drained, moderately fertile soils are optimal. In pots, a free-draining, medium-fertility, loam-based mixture is recommended.
Agronomy
Mexican oregano is propagated by seed, by basal or nodal softwood cuttings or by semi-hardwood cuttings. It is predominantly collected from the wild. In cultivation, high soil fertility or ample fertilizer application and abundant water supply result in increased leaf size but reduced flavour. In the southern United States it is grown as an annual. In Mexico, harvesting starts mid-September, when foliage is at its maximum, and it continues until the first frosts occur, usually in November at higher altitudes. Harvested shoots and leaves are used fresh or dried and stored in airtight containers. It is recommended to dry the branches upside down and away from direct light. In Mexico, picked leaves are generally spread on the ground and dried in the sun for 4-5 days. Grinding may lead to loss of chemical components and ground material has less aroma and freshness.
Genetic resources and breeding
There seems to be some danger of genetic erosion, because natural Mexican oregano populations in Mexico are overharvested. It is not known if germplasm collections and breeding programmes exist.
Prospects
At present, Mexican oregano is not cultivated in South-East Asia. However, interest in oregano is increasing in Japan and other Asian countries, including Malaysia, the Philippines and Thailand. This is largely due to the popularity of fast-food chains, which offer Italian and Mexican-style dishes flavoured with oregano. With respect to export production, the prospects for Mexican oregano are less promising than those for Origanum species, because the latter have a wider market and fetch higher prices on the world market. For both types of oregano, only clean material of acceptable colour is exportable, and new producers must be aware of the strict quality specifications.
Literature
- Greenhalgh, P., 1980. Production, trade and markets for culinary herbs. Tropical Science 22(2): 159-188.
- Lawrence, B.M., 1996. Progress in essential oils. Perfumer & Flavorist 21(3): 55-68.
- Morton, J.F., 1981. Atlas of medicinal plants of Middle America (Bahamas to Yucatan). C.C. Thomas Publisher, Springfield, Illinois, United States. pp. 745-749.
- Olivier, G.W., 1997. The world market of oregano. In: Padulosi, S. (Editor): Oregano. Promoting the conservation and use of underutilized and neglected crops 14. Proceedings of the IPGRI International Workshop on Oregano, 8-12 May 1996, CIHEAM, Valenzano (Bari), Italy. Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany and International Plant Genetic Resources Institute, Rome, Italy. pp. 142-146.
- Small, E., 1997. Culinary herbs. National Research Council of Canada. NRC Research Press, Ottawa, Canada. pp. 329-333.
- Tucker, A.O. & Maciarello, M.J., 1994. Oregano: botany, chemistry, and cultivation. In: Charalambous, G. (Editor): Spices, herbs and edible fungi. Elsevier, Amsterdam, the Netherlands. pp. 439-456.
Sources of illustrations
Small, E., 1997. Culinary herbs. National Research Council of Canada. NRC Research Press, Ottawa, Canada. Figs 200 & 201, pp. 330 & 331. Redrawn and adapted by P. Verheij-Hayes.
Authors
H.C. Ong & M. Brink
