Leucas (PROSEA)
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Introduction |
Leucas R.Br.
- Protologue: Prodr.: 504 (1810).
- Family: Labiatae
- Chromosome number: x= 11; L. aspera, L. lavandulifolia, L. zeylanica: 2n= 22
Major species
- Leucas aspera (Willd.) Link,
- L. lavandulifolia J.E. Smith,
- L. zeylanica (L.) R.Br.
Vernacular names
- (Petit) tombé (Fr, Réunion)
- Indonesia: paci-paci (general), lenglengan (Javanese).
Origin and geographic distribution
Leucas comprises about 80 species, of which 55-60 occur in southern and tropical Africa and Arabia, and about 25 species from Iran to China, Malesia and the Pacific. The genus has its highest species richness in East Africa.
Uses
In general, the crushed leaves of Leucas are applied to wounds, sores, especially those of the eyes and nose, chronic skin diseases, such as psoriasis and scabies. The crushed leaves are also used to treat mild fevers, colds, rheumatism and snake bites, and as a decoction against roundworm, mainly for children. The leaves of L. lavandulifolia and L. zeylanica are also used as a poultice to treat itch, headaches and vertigo. In Indonesia, the leaves may be taken externally or internally as a sedative, useful to treat convulsions, epileptic seizures, coughing spasms, and other nervous disorders. In India, the smoke of burnt dried leaves of L. aspera is used as an insecticide. In the Mascarenes, the plant is given for amenorrhoea, but in India the plant may be used for birth control. In Malesia, L. lavandulifolia is used as a gargle to remove mucus. A decoction of the leaves is considered a good stomachic, and is applied, internally and externally, to treat colic of children or saccharomycosis of horses. A decoction of the roots is sometimes used for inflamed callosity. Like L. zeylanica, it is also considered stimulant and diaphoretic.
Leucas species are aromatic herbs, L. aspera and L. lavandulifolia are considered fragrant, but L. zeylanica has an unpleasant smell and a bitter taste. In India and Malesia, all three species are locally used as a pot herb or grown in the garden for use as a condiment, fresh, dried or fried.
In Malesia, cattle will only eat L. lavandulifolia when other food is scarce. The white flowers are offered in temples.
Production and international trade
Leucas is usually cultivated in home gardens for use in local medicine and as a pot herb, and has not entered international trade.
Properties
Only little information can be found in the literature about the phytochemistry of L. aspera. The shoots are reported to contain an alkaloid (without further specification) and a series of fatty acids derived from triacontane, e.g. 28-hydroxypentatriacontan-7-one, 28-hydroxypentatriacontan-2-one, 1-hydroxytetratriacontan-4-one, 5-acetoxytriacontane, dotriacontanol and 32-methyltetratriacontan-8-ol. Extracts of L. aspera, however, are reported to display several biological activities. An alcoholic extract of the leaves shows anti-bacterial activity against Micrococcus pyogenes var. aureus, Escherichia coli, and several other bacteria. Furthermore, a chloroform extract, in the form of an 0.5% or 10% ointment, was found to be effective in the treatment of Trichophyton verrucosum ringworm in cattle. A water-soluble leaf extract was shown to be very effective in inhibiting egg hatch of the nematode Meloidogyne arenaria.
The same extract also completely inhibited conidial germination of the fungus Drechslera oryzae, in vitro. No antifertility activity was shown in a test with an extract of whole L. aspera plants for postcoital antifertility activity in female albino rats. The smoke of the powdered leaves of L. aspera, thrown on burning charcoal, was highly repellant and toxic to the mosquitoes Armigeres subalbatus and Culex quinquefasciatus. The leaf extract significantly reduced larval survival, pupation and adult emergence of the mosquito Anopheles stephensi in a dose dependent way, and also significantly increased adult repellence and ovipositional deterrence.
Only general information about phytochemical compounds is available for L. lavandulifolia. Without further specification the species is reported to contain alkaloids, steroids, triterpenes, flavonoids and tannins. More information can be found on biological activities of the extracts.
A methanol extract of the herb, in the form of an ointment or as an injection, was examined in rats for its wound healing activity in two types of wounds, the excision and the incision wound models. Both routes of administration showed significant responses in both wound types tested, in terms of contracting ability, wound closure time, tensile strength and regeneration of tissues at the wound site. The methanol extract was also investigated for its effects on a cough model induced by sulphur dioxide gas in mice. It exhibited significant antitussive activity in a dose-dependent manner, when compared with a control. Its effect is comparable to that of codeine phosphate, as a prototype antitussive agent. Furthermore, an ethanol extract of the leaves showed significant inhibitory activity against castor oil induced diarrhoea and PGE2 induced enteropooling in rats. The extract also showed a significant reduction in gastro-intestinal mobility in rats using charcoal meals as test model.
L. zeylanica yields a small quantity of essential oil, reported to contain an alkaloidal substance.
Description
- Mostly annual, strong smelling, much branched herbs or undershrubs, stems and leaves often villous.
- Leaves decussate, crenate-dentate-serrate or subentire; petiole short or absent; stipules absent.
- Inflorescence composed of distant verticillasters with numerous axillary, bisexual, irregular, subsessile flowers, sometimes forming terminal, capitate clusters.
- Calyx tubular-infundibuliform, 8-10-veined, 8-10-toothed, teeth equal or posterior one largest; corolla 2-lipped, upper lip erect, entire, concave, densely villous, lower lip 3-fid, spreading, central lobe very large, tube slender, often not exserted, with a hairy ring inside or not, white, sometimes purple; stamens 4, didynamous, filaments inserted in the corolla tube, upper pair shorter, all ascending under upper lip, hairy, anther-cells nearly in line with each other, confluent, reddish; style subulate, 2-branched, upper branch minute; disk entire or lobed, equal or unequal-sided.
- Fruit consisting of 4 dry 1-seeded schizocarpous nutlets enclosed in the persistent calyx, nutlets trigonous, obtuse, smooth.
- Seedling with epigeal germination; hypocotyl densely hairy; cotyledons broadly ovate, 6 mm long, hairy, emarginate; epicotyl 3 mm long, 4-angular, hairy, first leaves 2, elliptical.
Growth and development
Leucas is pollinated by bees, moths and flies. Flowering is throughout the year, whenever sufficient water is available. L. aspera shows a high tolerance to copper and zinc concentrations in polluted soil.
Other botanical information
Leucas belongs to the subfamily Lamioideae, and is closely related to the small genera Acrotome and Leonotis. The exact number of species in Leucas is not clear as no recent revision of all taxa is available.
Ecology
Leucas occurs in various habitats, from seasonal to perhumid areas, often as a weed of crops or as a ruderal, locally often common, from sea-level to 1500 m altitude.
Propagation and planting
Leucas is propagated by seed.
Husbandry
Of all Leucas species, L. lavandulifolia is becoming a serious weed in sugarcane fields in Malesia. In banana plantations in India, the application of paraquat at 3 l/ha controls L. lavandulifolia sufficiently. L. aspera occurs mainly as a weed in sunflower and in rice in India.
Diseases and pests
Warty galls often occur on young L. lavandulifolia stems and L. zeylanica leaves. They are caused by the fungus Synchytrium rytzii. L. aspera is a host for the fungal pathogen Septoria bakeri and also for the root-knot nematode Meloidogyne javanica.
Harvesting
The leaves or flowers of Leucas are collected from gardens, where they often grow as pot herbs. Whole plants are collected from the wild, whenever the need arises.
Handling after harvest
The leaves or whole plants of Leucas are used fresh or dried and powdered.
Genetic resources and breeding
In view of their wide distribution, L. aspera, L. lavandulifolia and L. zeylanica are not endangered or liable to genetic erosion. In addition, they are often cultivated as pot herbs.
Prospects
Extracts of Leucas show some interesting biological effects, e.g. in the field of treatment of fungal skin infections, wound-healing activity, anti-cough activity and insect repellent activity. More research is needed, however, to isolate the compounds or complexes responsible for these activities, in order to fully evaluate their potentials.
Literature
- Keng, H., 1978. Labiatae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Series 1, Vol. 8. Sijthoff & Noordhoff International Publishers, Alphen aan den Rijn, the Netherlands. pp. 337-341.
- Mukherjee, P.K., Saha, K., Murugesan, T., Mandal, S.C., Pal, M. & Saha, B.P., 1998. Screening of anti-diarrhoeal profile of some plant extracts of a specific region of West Bengal, India. Journal of Ethnopharmacology 60(1): 85-89.
- Murugan, K. & Jeyabalan, D., 1999. Effect of certain plant extracts against the mosquito Anopheles stephensi Liston. Current Science 76(5): 631-633.
- Ryding, O., 1998. Phylogeny of the Leucas group (Lamiaceae). Systematic Botany 23(2): 235-247.
- Saha, K., Mukherjee, P.K., Das, J., Pal, M. & Saha, B.P., 1997. Wound healing activity of Leucas lavandulaefolia. Journal of Ethnopharmacology 56(2): 139-144.
- Saha, K., Mukherjee, P.K., Murugesan, T., Saha, B.P. & Pal, M., 1997. Studies on in vivo antitussive activity of Leucas lavandulaefolia using a cough model induced by sulfur dioxide gas in mice. Journal of Ethnopharmacology 57(2): 89-92.
Selection of species
Authors
- Marfu’ah Wardani
