Limnophila (PROSEA)
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Introduction |
Limnophila R.Br.
- Protologue: Prodr.: 442 (1810).
- Family: Scrophulariaceae
- Chromosome number: x= 17, 34; L. aromatica: 2n= 34, 68, L. indica: 2n= 34, 68, L. repens: 2n= 68, L. rugosa: 2n= 34
Major species
- Limnophila aromatica (Lamk) Merr.,
- L. indica (L.) Druce.
Origin and geographic distribution
Limnophila consists of 35-37 species from the Old World tropics and subtropics, with tropical Asia as its centre of distribution. L. indica is most widely distributed, throughout the range of the genus. About 15 species occur in South-East Asia, some of them are endemic, and 6 species are endemic to Africa. L. sessiliflora (Vahl) Blume has escaped from cultivation in southern North America.
Uses
In Malaysia, the more strongly aromatic Limnophila are considered medicinal, rather than a condiment. The smell is agreeable and resembles that of turpentine, or a mixture of cinnamon and cloves or cinnamon and citrus. In Indonesia and Peninsular Malaysia, the sap of the leaves of L. aromatica is used to clean wounds and sores on the legs although it is considered rather strong. A decoction of the leaves is given in fevers but also to promote appetite, and as an expectorant to clear mucus from the bronchial tubes. In India and Thailand, the plant is used as a cooling agent in fevers, and given to nursing mothers as a galactagogue. In Vietnam, the whole plant is used for its diuretic and anti-spasmodic action, against gravel in the kidneys, as a disinfectant for wounds and for haematuria; also for cough, snakebite and skin diseases. In China, the plant is used for the treatment of intoxication, body pains and for menstrual problems. In Malaysia and Indonesia, L. erecta has the same medicinal uses as L. aromatica. In the Philippines, an infusion of the leaves of L. indica is used for dysentery and dyspepsia. In India, the plant is considered antiseptic, and the juice is rubbed on the body for strong fevers. A liniment is made from the plant with coconut oil and used in elephantiasis. Internally, the juice is given in dysentery, combined with cumin (Cuminum cyminum L.) and other aromatic plants. In Indonesia, a decoction of L. rugosa is used externally to cure itching eyes, and internally for mild gonorrhoea and impotence.
In Indo-China, Thailand and Indonesia, L. aromatica, L. erecta, L. indica and L. rugosa are also eaten as a condiment or sidedish, raw, steamed or cooked. L. aromatica is thought to calm the stomach after eating durian (Durio zibethinus Murray). L. aromatica can also be grown as an ornamental, because of its attractive flowers.
Production and international trade
Limnophila is traded on a local scale only, and is found fresh in markets, or dried in Chinese herbalists stores.
Properties
L. aromatica contains 0.13% essential oil, the terpenesδ-limonene andδ-perillaldehyde being important constituents. The bactericidal activities of this essential oil against Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus were similar to those of a streptomycin and chloramphenicol reference. The activities of the essential oil against Aspergillus niger, Candida albicans and Rhizopus oryzae, however, were more marked than those of griseofulvin as reference. Phytochemical analysis also showed the presence of 2 flavonoids, nevadensin (= 5,7-dihydroxy-6,8,4'-trimethoxyflavone) and salvigenin (= 5-hydroxy-6,7,4'-trimethoxy flavone) as well as 2 phenolics, caffeic acid and chlorogenic acid. The related (methylenedioxy type) flavonoid 5-hydroxy-6,8-dimethoxy-3',4'-methylenedioxyflavone has also been isolated from L. indica.
The essential oil of L. rugosa contains linalool (0.1%), estragole (22%), cis-anethole (0.03%), anisaldehyde (0.05%), trans- anethole (75%), anisyl acetone (0.03%), caryophyllene (0.08%), humulene (0.15%) andα-bulnesene (0.01%). Also the compounds 3β-hydroxy-20(29)-en-27-oic acid, nevadensin, and demethoxysudachitin were isolated. The flavonoid nevadensin, administered intravenously (3.1 mg/kg), exhibited a hypotensive effect on both normotensive and spontaneous hypertensive rats under pentobarbital anaesthetization. After administration of nevadensin, the mean arterial pressure decreased by about 50 mm Hg for 30 minutes.
The essential oil of L. repens (Benth.) Benth. (synonym L. conferta Benth.), an aquatic herb also occurring in South-East Asia, containsα-phellandrene (52.2%) and thymol (38.2%). The antifungal activity of a 1:50 dilution in ethylene glycol was found to be of the same order of magnitude as that of griseofulvin (100 μg/0.1 ml) for Aspergillus niger, Candida albicans and Rhizopus nigricans (synonym R. stolonifer). Against dermatophytes (Trichophyton mentagrophytes and Microsporum gypseum), the oil at a concentration of 100 μg/ml inhibited growth whereas miconazole was effective at a concentration of 10 μg/ml. The oil also possessed good anthelmintic activity against Taenia sp. and Ascaris galli. The crude alcoholic extract showed significant reduction in the epithelization period compared with that of controls in excision wound models. Nevadensin isolated from the plant showed good anti-inflammatory activity in an acute inflammation model and exhibited moderate cytotoxic activity and anti-tubercular activity.
Description
- Annual or perennial, aquatic or semi-aquatic herbs, often aromatic when bruised, glabrous or hairy; stems erect or prostrate and rooting at the nodes, simple or branched.
- Submerged leaves verticillate, pinnatifid, glabrous; aerial leaves opposite to verticillate, entire to serrate, laciniate or pinnately divided, punctate; petiolate or not.
- Inflorescence a lax or compact, terminal or axillary spike or raceme, or flowers solitary and axillary; bracteoles 0 or 2.
- Flowers bisexual, slightly zygomorphic, 5-merous; calyx tubular, deeply 5-lobed, lobes subequal, tube with 0–-5 or 10 prominent veins; corolla tubular or infundibuliform, 5-lobed, bilabiate, adaxial lip outside in bud, entire or 2-lobed, abaxial lip 3-lobed, erect or spreading; stamens 4, included, didynamous, filaments filiform, anthers free, loculi stipitate; ovary superior, glabrous, style filiform, deflexed at apex, stigma bilamellate.
- Fruit an ellipsoid to globose capsule, septically 4-valved, valves bifid, with numerous seeds.
- Seed prismatic, small, 0.2-–0.3 mm long, both ends truncate.
Growth and development
Limnophila can be found flowering and fruiting throughout the year. The production of fruits by cleistogamy on submerged stems was found in several Limnophila species, including L. sessiliflora, but has not been observed in L. indica. Hybridization is recorded from tetraploid L. indica and L. sessiliflora, both common aquarium plants.
Several varieties have been distinguished in L. indica by earlier authors, but it was found that factors such as light intensity, daylength, water depth and water flow produced these varieties. In Sri Lanka, the flowers of L. indica open between 10-15 h.
Other botanical information
Limnophila belongs to the tribe Gratioleae and subtribe Stemodiinae, and is closely related to Stemodia and Morgania. Limnophila is divided into 4 sections: sect. Limnophila (e.g. L. indica) has finely divided submerged leaves, and aerial leaves with parallel veins, section Connatae has similar aerial leaves, but lacks submerged leaves, section Integrifolieae (e.g. L. rugosa) has pinnately veined leaves and a calyx without striations, while section Striatae (e.g. L. aromatica, L. erecta) has similar leaves as the latter but a striate calyx. Most Limnophila species show a large variation in form of the leaves, hairiness and habit.
Ecology
All Limnophila are aquatic or semi-aquatic herbs occurring in marshes, along riversides or forest paths, mostly at low altitudes. Limnophila is also a weed of rice fields.
Propagation and planting
Limnophila normally propagates by seeds or rooted stems. Also, root tips (1 cm long) from in vitro grown plants of L. indica have been cultured in liquid medium with 2% sucrose. The explants floated horizontally on the surface, became green, and their tips started to grow geotropically into the medium. In 4 weeks, 4-6 shoot buds each were differentiated in 84.5% of the cultures. No buds formed at the cut end or near the growing root tip. Histological studies of the roots showed that the buds originated from proliferating cortical cells, which had prominent chloroplasts and starch grains. The shoot buds grew successfully into entire plants.
Husbandry
L. aromatica is not easily cultivated as it needs a permanent water supply, and the tender, fleshy stems can be easily damaged.
Harvesting
Plants of L. aromatica are harvested from the wild in Vietnam, when they are at least a year old. Young plants are used as a condiment.
Handling after harvest
In Vietnam, the plants of L. aromatica are dried before use.
Genetic resources and breeding
All Limnophila species mentioned here have a large area of distribution, either naturally or as a result of cultivation, and do not seem to be at risk of genetic erosion. There are no known breeding programmes.
Prospects
Essential oils and flavonoids of Limnophila show interesting pharmacological activities. More research is, however, needed to fully evaluate this potential. The plants might be of interest as a local source of e.g. antifungal or anthelmintic preparations.
Literature
- de Guzman, C.C. & Siemonsma, J.S. (Editors), 1999. Limnophila rugosa (Roth) Merrill. Plant Resources of South-East Asia No 13. Spices. Backhuys Publishers, Leiden, the Netherlands. p. 257.
- Liu, M.C., Chen, Z.S., Chung, L.C., Yang, M.S., Ho, S.T. & Chen, M.T., 1991. Studies on hypotensive constituents of Limnophila rugosa. Chinese Pharmaceutical Journal 43(1): 35-–40.
- Perry, L.M., 1980. Medicinal plants of East and Southeast Asia. Attributed properties and uses. MIT Press, Cambridge, Massachusetts, United States & London, United Kingdom. p. 383.
- Philcox, D., 1970. A taxonomic revision of the genus Limnophila R.Br. (Scrophulariaceae). Kew Bulletin 24: 101–-170.
- Rao, J.V., Aithal, K.S. & Srinivasan, K.K., 1989. Antimicrobial activity of the essential oil of Limnophila gratissima. Fitoterapia 60(4): 376-–377.
- Rao, S. & Ram, H.Y.M., 1981. Regeneration of whole plants from cultured root tips of Limnophila indica. Canadian Journal of Botany 59(6): 969-–973.
Selection of species
Authors
- G.H. Schmelzer
