Thymus vulgaris (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

1, flowering branches; 2, flower

Thymus vulgaris L.

Protologue: Sp. pl.: 591 (1753).

Family: Labiatae

Chromosome number: 2n = 30

Synonyms

Thymus aestivus Reuter ex Willk. & Lange (1868),
T. ilerdensis F. Gonzalez ex Costa (1877),
T. webbianus Rouy (1884).

Vernacular names

Thyme, garden thyme, common thyme (En)

Thym vulgaire, thym des jardins (Fr)

Indonesia: timi

Note: the word "thyme” or combinations thereof does not refer exclusively to the botanical species T. vulgaris; the taxonomy of the genus Thymus L. is badly known and the word "thyme” in the literature can refer to a great number of different taxa.

Origin and geographic distribution

Thyme originated from the European part of the Mediterranean (from Portugal to Greece) where it is also cultivated. At present it is cultivated worldwide in non-tropical regions (e.g. in most European countries, the Mediterranean area, Russia, Canada, United States, China and Japan), but occasionally also at higher altitudes in the tropics (e.g. in Java (Indonesia) and the Philippines).

Uses

Since ancient times the leaves and flowering tops of thyme have been used fresh and dried as a condiment and culinary herb, and the entire plant (excluding the roots) for the distillation of essential oil. Thyme honey is well known for its fine flavour and sweetness. Thyme is used to flavour numerous kinds of food, such as butter, cheese, fish, meat, olives, onions, pickles, sauces, soups, stews, stuffings and vinegar. The essential oil is used to scent perfumes and soap but also to flavour food. In the United States the regulatory status "generally recognized as safe” has been accorded to thyme (GRAS 3063) and thyme oil (GRAS 3064). The maximum permitted level of thyme oil in food products is about 0.003%.

Thyme has a long history in traditional medicine and has been reportedly used in bronchitis, catarrh-colic, diabetes, fever, sore throat, spleen disorders, uterine disorders and warts, and is considered antispasmodic, carminative and tonic. Thyme tea (1 teaspoon fresh leaves steeped in 1 cup boiling water) is believed to cure headache and tumours of the digestive tract, whereas thyme juice with vinegar is said to cure tumours and cancers. In Indonesia the fluid extract and syrup from the shoot are used traditionally as a cough medicine. The smoke of burning thyme is supposed to repel insects. The essential oil is a strong germicide, used as disinfectant and an antiseptic gargle and mouthwash but also as fungicide and insecticide.

Thymus spp. are often grown as ornamentals.

Production and international trade

Annual world production of thyme is estimated at 1500 t, mainly produced around the Mediterranean. Statistics are rare. In 1988 the United States imported more than 900 t unprocessed thyme valued at US$ 2 million (mostly from Spain) and 18 t of processed thyme valued at US$ 20 000 (mostly from Denmark). Annual production of thyme essential oil is estimated at 30 t, with a value of US$ 1.5 million, but this estimate refers to essential oils of several Thymus species (T. capitatus (L.) Hoffm. & Link, T. mastichina L., T. pulegioides L., T. vulgaris and T. zygis L.). For T. vulgaris alone the annual essential-oil production is estimated at 4 t.

Properties

Per 100 g edible portion ground dried thyme contains: water 7-8 g, protein 7-9 g, fat 5-7 g, carbohydrates 44-45 g, fibre 19-24 g, ash 12-13 g (Ca 1.9 g, P 0.2 g, Fe 0.1 g, Mg 0.2 g, Na 55 mg, K 0.8 g, Zn 6 mg), vitamin A 3800 IU, thiamine 0.5 mg, riboflavin 0.4 mg, niacin 4.9 mg, phytosterols 0.2 g, saturated fatty acids total 2.7 g, mono-unsaturated 0.5 g and poly-unsaturated 1.2 g. The energy value is 1155 kJ/100 g.

Upon distillation, thyme usually yields (1-)2-2.5(-3)% essential oil. Thyme essential oil is a pale, yellowish-red liquid with a rich, sweet, aromatic, herbaceous odour, yielding a sweet, phenolic, somewhat medicinal perception upon drying out. The taste is sharp, biting, warm and spicy. The characteristic constituents of the oil are thymol and carvacrol; other more variable components are 1,8-cineole, citral, camphor, carvone, monoterpene alcohols and their acetates and sesquiterpene alcohols. The essential oil from T. vulgaris may contain up to 30% monoterpene hydrocarbons and more than 50% 1,8-cineole, camphor and monoterpene alcohols, whereas thymol and carvacrol are present at levels lower than 5%. The essential oil from T. zygis may contain more than 50% thymol and carvacrol, with up to 30% monoterpene hydrocarbons and less than 10% monoterpene alcohols and esters.

The seeds yield 37% of a drying oil consisting mainly of linolenic, linoleic and oleic acids. Triterpenoid saponins, flavones, ursolic acid, caffeic acid, tannins and resins also occur in the herb.

Thyme oil itself is quite poisonous. Thymol has caused dermatitis in dentistry and when used in toothpaste. Thyme oil in bath preparations has been reported to cause hyperaemia and severe inflammation.

A monograph on the physiological properties of thyme oil has been published by the Research Institute for Fragrance Materials (RIFM).

Composition

Thyme oil (from Denmark) (Source: Venskutonis et al., 1996.)

39.1% thymol
24.2% para-cymene
11.0% γ-terpinene
5.1% carvacrol
2.2% linalool
2.1% myrcene
1.7% trans-sabinene hydrate
1.6% α-pinene
1.6% α-thujene
1.5% α-terpinene
1.3% β-caryophyllene
1.2% borneol
1.0% camphene
0.8% 1-octenol-3
0.7% terpinen-4-ol
0.6% methyl thymol
0.6% 1,8-cineole
0.5% methyl carvacrol
0.5% β-pinene
0.4% limonene
0.4% cis-sabinene hydrate
0.2% camphor
0.2% caryophyllene oxide
0.2% 3-octanol
0.1% δ-3-carene
0.1% cis-dihydrocarvone
0.1% β-phellandrene
0.1% α-phellandrene
0.1% germacrene D
0.1% (Z)-nerolidol
0.1% α-bergamotene
0.1% α-thujone
0.1% neral
0.1% terpinolene
0.1% β-ionone
0.1% α-terpineol
trace tricyclene
trace citronellol
trace nerol
trace aromadendrene
trace β-bisabolene
trace bornyl acetate
trace δ-cadinene
trace γ-cadinene
trace T-cadinol
trace trans calamenene
trace p-cymen-8-ol
trace β-elemene
trace γ-eudesmol
trace eugenol
trace farnesol (unknown isomer)
trace geranial
trace geraniol
trace geranyl acetate
trace (Z)-3-hexenol
trace α-humulene
trace α-ionone
trace isoborneol
trace isomenthone
trace isopulegol
trace lynalyl acetate
trace menthone
trace methyl chavicol
trace α-muurolene
trace γ-muurolene
trace (E)-nerolidol
trace (E)-β-ocimene
trace (Z)-β-ocimene
trace sabinene
trace thymyl acetate
100.0% total

Thyme oil (from New Zealand) (Source: McGimpsey et al., 1994.)

37.0% para-cymene
22.5% thymol
10.0% γ-terpinene
6.2% carvacrol
4.1% linalool
3.0% borneol
2.6% β-caryophyllene
2.2% methyl carvacrol
1.9% methyl thymol
1.5% myrcene
1.2% caryophyllene oxide
1.2% 1,8-cineole
1.0% limonene
0.9% camphene
0.9% β-pinene
0.8% camphor
0.8% germacrene D
0.6% α-pinene
0.6% α-thujene
0.5% terpinen-4-ol
0.5% α-terpineol
99.9% total

Adulterations and substitutes

Thyme oil is sometimes adulterated by the addition of terpenes and lowering of phenol content. If synthetic carvacrol is used it can be detected by non-crystallizable phenols.

Description

Small, erect or ascending, aromatic, evergreen perennial subshrub, 10-30(-50) cm tall, often copiously branched. Stem and branches stiff and woody, obscurely quadrangular, faintly furrowed in the upper part, with very short internodes; branchlets very densely coated with minute grey hairs.
Leaves opposite, sometimes seemingly whorled by the presence of axillary leaves; petiole up to 0.5 mm long; blade linear to elliptical, 3-8 mm × 0.5-2.5 mm, margin entire but recurved and not ciliate, coriaceous, both surfaces densely minutely hairy and dotted with numerous orange-brown oil glands.
Inflorescence composed of axillary many-flowered whorls, the whole forming a terminal spike up to 5 cm × 1 cm; bracts similar to the leaves but somewhat wider and sometimes with almost flat margins, grey-green.
Pedicel 1-3 mm long; calyx tubular, 3-4 mm long, short-haired, 2-lipped, upper lip with 3 very short triangular teeth, lower lip with 2 longer teeth; corolla tubular, 2-lipped, 4-6 mm long, upper lip 2-lobed, lower lip 3-lobed, lilac to pale purple; stamens 4, didynamous, exserted; pistil with 4-lobed ovary and single style which is 2-lobed at top.
Fruit consisting of 4 one-seeded, brown, globose nutlets about 1 mm long.

Growth and development

Thyme can be grown as an annual or as a perennial. Flowering starts about 2-3 months after sowing and pollination is mainly by honeybees, but some self-pollination also occurs. In natural populations of T. vulgaris often more than 50% of the plants have functionally male-sterile flowers in addition to plants with bisexual flowers. Seed set is usually abundant. Commercial plantations are renewed after 2-3(-5) years because the crop tends to become woody, straggling and low-yielding.

Other botanical information

Thymus is confined to the Old World and is taxonomically badly known. The estimated number of species ranges from 35-350 and this great divergence is due to the existence of numerous local Thymus taxa which some consider to be separate species, but others see as forms of complex large species. When growing under favourable conditions, most Thymus taxa have aromatic leaves and flowers and are used locally as a condiment, ornamental plant and for honey production. Only a few are grown commercially.

The major useful species (besides T. vulgaris) are mentioned below, but their identity needs better investigation:

T. caespititius Brot., Azores thyme, native to north-western Spain, Portugal, Canary Islands and the Azores. Its fresh leaves are used to flavour foods.

T. capitatus, Spanish oregano, native to the Mediterranean from Portugal to Israel and collected from the wild for its essential oil (Spanish oregano oil, annual production about 7 t, mainly used to scent toiletries and to flavour foods).

T. ×citriodorus (Pers.) Schreb., lemon thyme, the leaves smell of lemon. It is a hybrid between T. pulegioides L. and T. vulgaris, often appearing spontaneously in Europe in areas where T. vulgaris is cultivated. It is the principal thyme of commerce after garden thyme, also as an ornamental. Much confusion exists about the term "lemon thyme”, because several other species also have lemon-scented forms.

T. herba-barona Lois., caraway thyme, a native of Corsica and Sardinia, and a popular condiment for meat.

T. mastichina, mastic thyme or Spanish marjoram, native to Portugal and Spain and collected from the wild for its essential oil (Spanish marjoram oil, annual production about 36 t, used to flavour meat sauces and soups).

T. praecox Opiz, creeping thyme, native to central Europe and a popular ornamental. In a wide species concept it is considered as belonging to T. serpyllum L. The taxon is very complex and many subdivisions exist.

T. pulegioides, large wild thyme of Europe, source of about 2 t commercial essential oil annually. It is widespread in Europe and is very variable.

T. quinquecostatus L., Japanese thyme, native to north-eastern China and Far-Eastern Russia and grown in Japan and Korea where it is used to flavour soup and meat.

T. serpyllum L., wild thyme of Europe, a complex species growing wild all over Europe and used as a culinary herb and for essential-oil production.

T. zygis, Spanish thyme, native to Portugal and Spain. Its leaves are used as a condiment and to produce Spanish thyme oil (annual production about 25 t, representing 85% of the total thyme-oil production).

T. vulgaris is very variable in shape of leaves, bracts and inflorescence and many subdivisions exist in the botanical literature. For the cultivated forms a classification into cultivar groups and cultivars would be most appropriate, but is only possible after a thorough revision of the species and its relatives. The species is extremely variable: there are cultivars with narrow, broad and variegated leaves, and cultivar group distinction may also be possible based on differences in the composition of the essential oils.

Ecology

The natural habitat of thyme is the Mediterranean area, with hot, dry summers and cool, wet winters. Thyme grows at temperatures between 4-28°C, but optimally at 16°C. It is hardy to at least -15°C. It is drought tolerant but some supplementary water during dry periods is beneficial. In cultivation thyme prefers warm, sunny conditions with moderately fertile but well-drained soils such as sands or sandy loams, preferably slightly alkaline. In heavy, wet soils, thyme is short-lived and less aromatic. In South-East Asia it should be grown at higher elevations. Thyme is cultivated in the Philippines in the cool area of Cavite, about 600 m above sea-level.

Propagation and planting

Thyme seed can be stored for more than 6 years in airtight containers at 20°C with only slight loss of viability. Thyme is most easily propagated by seed, either directly in the field or in a nursery with later transplanting. The tiny seeds are covered with a thin layer of soil to avoid desiccation. Germination takes 2-3 weeks at 21°C. Plant spacing in the field is 10-15 cm between plants in the row and 20-25 cm between rows. If grown first in the nursery, young plants are ready for transplanting when they are 5-8 cm tall. Thyme can also be propagated vegetatively by cuttings, layering or root division.

Husbandry

Mulching of thyme is practised to control weeds, particularly in new plantings, and to help the crop to overwinter. Stem tips should be pruned regularly to encourage bushy growth. Thyme has been called the "poor man's herb”, because it can be grown in various soils without adding fertilizers. A moderate application of well-balanced fertilizer or composted manure is beneficial. If the crop receives additional irrigation, the soil should be allowed to dry between applications.

Diseases and pests

Thyme seldom suffers seriously from diseases and pests. A major problem can be caused by dodder (Cuscuta sp.) which sometimes overgrows thyme completely.

Harvesting

Thyme is harvested just before or during flowering, once during the first year of growth and 2-4 times in the succeeding years. Plants are cut 8-12 cm above the ground manually or mechanically. Cutting too low may cause plant death.

Yield

In the first year annual yields of thyme are about 5 t/ha fresh or 1 t/ha dried herb, in the following years about 12-14 t/ha fresh or 2-3 t/ha dried. The frequency of harvest affects the yield; when harvested every 4 months an annual yield of 4.6 t/ha was obtained as compared with 2.6 t/ha when harvesting was every 2 months.

Handling after harvest

When intended for the fresh market, the harvested shoots of thyme are simply cooled and bunched or packed in polythene bags. The shoots can also be dried, either by spreading them thinly in trays with muslin or fine wire-mesh bottoms in a well-ventilated, shaded area to preserve the greyish-green colour, or by drying artificially at temperatures between 29-43°C. After drying, leaves and flowering tops are stripped from the stems and stored in polythene bags. For essential-oil distillation, fresh but dry material from which any woody and wilted parts have been removed should be used immediately after harvesting.

Genetic resources

Small germplasm collections of thyme are available at most gene banks in Europe, e.g. in France (Conservatoire des Plantes Médicinales, Aromatiques et Industrielles, Milly-la-Forêt) and in Portugal (Portuguese Plant Germplasm Bank, Braga).

Breeding

Breeding prospects for thyme are promising because of the natural high rate of male sterility and the ease of vegetatively propagating desired types. One of the breeding objectives is to obtain cultivars with a desirable essential-oil composition. The Mediterranean T. vulgaris consists of 6 chemotypes with different major monoterpenes. The nature of these monoterpenes is controlled by a series of loci, probably with dominant and recessive alleles. Epistatic relationships between these loci have been interpreted by assuming the terpenes as end-products of branches from the same biosynthetic pathway. The most dominant types, which correspond to the monoterpenes produced at the beginning of the chain, show the most important genetic diversity.

Prospects

The demand for thyme is expected to grow faster than the demand for most other culinary herbs, particularly in the major European markets. However, the current market for dried herbs in general is not limited by supplies, and producers/exporters seeking entry will have to compete with traditional suppliers. Provision of a consistent high-quality product with good appearance can help newcomers in the trade to penetrate the market.

Literature

Assouad, M.W., Dommée, B., Lumaret, R. & Valdeyron, G., 1978. Reproductive capacities in the sexual forms of the gynodioecious species Thymus vulgaris L. Botanical Journal of the Linnean Society 77: 29-39.

Bean, W.J., 1980. Trees and shrubs hardy in the British Isles. Vol. 4 (Ri-Z). Eighth revised edition (editors: Clarke, D.L & Taylor, G.). John Murray, London, United Kingdom. pp. 589-592.

Farrel, K.T., 1985. Spices, condiments and seasonings. Van Nostrand Reinhold Co., New York, United States. pp. 217-220.

Halva, S. & Craker, L.E., 1996. Manual for northern herb growers. HSMP Press, Amherst, Massachusetts, United States. 101 pp.

Jalas, L., 1972. Thymus L. In: Tutin, T.G. et al. (Editors): Flora Europaea. Vol. 3. Cambridge University Press, London, United Kingdom. pp. 172-182.

Lawrence, B.M., 1998. Progress in essential oils. Perfumer & Flavorist 23(1): 39-50.

Perry, L.M., 1980. Medicinal plants of East and Southeast Asia. Attributed properties and uses. The MIT Press, Cambridge, Massachusetts, United States. p. 195.

Small, E., 1997. Culinary herbs. National Research Council of Canada. NRC Research Press, Ottawa, Canada. pp. 606-616.

Vernet, P., Gouyon, P.H. & Valdeyron, G., 1986. Genetic control of the oil content in Thymus vulgaris. A case of polymorphism in a biosynthetic chain. Genetica (The Hague) 69(3): 227-232.

Sources of illustrations

Small, E., 1997. Culinary herbs. National Research Council of Canada (NRC) Research Press, Ottawa, Canada. Fig. 393, p. 610. Redrawn and adapted by P. Verheij-Hayes.

Authors

S.H. Widodo