Indigofera (PROSEA Medicinal plants)
- Protologue: Sp. pl. 2: 751 (1753) ; Gen. pl. ed. 5: 333 (1754).
- Family: Leguminosae
- Chromosome number: x= 8; I. linnaei, I. tinctoria: 2n= 16
Origin and geographic distribution
Indigofera consists of about 700 species, and is widely distributed in the tropics and subtropics of Africa, the Americas, Asia and Australia. Africa is richest in species, but the southern Himalaya region is also comparatively rich. Approximately 35 species occur naturally in South-East Asia, 16 of which are found in the Malesian region. Additionally, several species have been introduced in South-East Asia.
Indigofera is used in traditional medicine in South-East Asia for various complaints, externally, e.g. to treat sores, ulcers and aphthae, as well as internally, e.g. to treat epilepsy and as a diuretic. Some Indigofera species are well-known dye plants throughout the world, especially I. arrecta Hochst. ex A. Rich. and I. tinctoria L., the leaves of which are also used in traditional medicine to treat epilepsy and nervous disorders, and to heal sores and ulcers. Several Indigofera species are used as a cover crop, green manure or fodder, e.g. I. hirsuta L. and I. suffruticosa Miller, both of which have medicinal applications: the leaves of the first are used to treat stomach complaints in the Philippines and Thailand, the roots of the second to treat stomach-ache and diarrhoea, the leaves against fever and the juice against diarrhoea in Malaysia. Seeds are used occasionally as a famine food, including those of I. linifolia and I. linnaei.
In Taiwan the roots of I. zollingeriana Miq. are used to treat stomach-ache and snakebites. In Burma (Myanmar) the roots of I. cassioides Rottler ex DC. (synonym: I. pulchella Roxb.) are applied to treat cough.
An ethanol extract from the leaves of I. oblongifolia showed in-vitro antibacterial activity against Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Small proteins or peptides in the leaves of I. oblongifolia show considerable in-vitro antibacterial and antifungal activity. These compounds probably play a role in the defence mechanism of the plant.
An extract of the above ground parts of I. tinctoria shows hypoglycaemic and central nervous system-depressant effects in rats, and potentiates pentobarbital sodium-induced sleep in mice. An ethanol extract possesses protective effects against carbon tetrachloride-induced liver damage in rabbits, rats and mice, as confirmed by histopathological studies.
Pharmacological research on I. arrecta supports its traditional use in Ghana, where an aqueous extract of leaves from immature shoots is administered orally to patients with diabetes mellitus. This extract prevented the development of hyperglycaemia in genetically obese diabetic mice. In tests with rats, an intraperitoneal administration of a hot water extract of dried leaves decreased the plasma glucose levels of fasting normoglycaemic rats, but did not prevent the rise in plasma glucose after an oral glucose load. It was suggested that the extract is insulinotropic and may require functional β-cells to be active. The extract was devoid of acute and subchronic toxic effects in tests with mice. Clinical test data suggest that the plant may not have overt toxic reactions in humans but could affect the immune status of users. A medicine based on I. arrecta for the management of peptic ulcer has been patented.
Many Indigofera species contain toxic compounds. The toxic effects of I. linnaei may well be attributed to the presence of nitropropanoyl esters that upon hydrolysis yield 3-nitropropanoic acid. This compound inhibits succiniate dehydrogenase and other essential respiratory enzymes. Several flavonoids have been isolated from Indigofera, including I. linifolia.
- Annual or perennial herbs or shrubs, with a taproot; branches spreading or ascending; indumentum consisting of 2-branched hairs.
- Leaves alternate, imparipinnate, sometimes trifoliolate or unifoliolate; stipules usually persistent. Inflorescence an axillary raceme, bracteate.
- Flowers bisexual, pedicellate; calyx campanulate, 5-toothed; corolla papilionaceous, standard without appendages, usually pubescent outside, wings usually with an auricle at base, keel with auricles at base and with lateral pockets; stamens 10, 9 connate and 1 free, all fertile, alternatingly shorter and longer; ovary superior, sessile, 1-celled, style curved upwards.
- Fruit a linear to globose pod, 1-20-seeded, dehiscent or not.
- Seeds globose to ellipsoid, cylindrical or quadrangular.
- Seedling with epigeal germination; cotyledons thick, short-lasting.
In Java flowering and fruiting of I. linifolia is limited to March-June, whereas I. linnaei and I. oblongifolia can be found flowering and fruiting throughout the year. I. linifolia and I. linnaei both have nodulating ability.
The large number of species makes a worldwide taxonomical study of Indigofera a daunting task. In many regions the genus has been incompletely studied, and in regions where a taxonomic revision has been accomplished, comparisons with other regions have usually not been done.
Most Indigofera species occur in open locations, such as grassland, roadsides and open deciduous forest, in the lowland. In South-East Asia several species are bound to monsoon areas. I. linifolia prefers an extremely dry monsoon climate.
Propagation of the Indigofera species treated here is by seed. Soaking for 5 minutes in concentrated H2SO4 increased the germination rate of I. oblongifolia seeds from 10% to 90%, whereas gibberellic acid was ineffective. In I. linifolia pretreatment with KNO3, 1-naphthalene acetic acid (NAA) and 3-indole acetic acid (IAA) proved to be effective in breaking seed dormancy, whereas for I. linnaei this did not work. Thiourea proved to be effective in both species.
In view of their wide distribution and presence in dry open habitats, the Indigofera species treated here do not appear to be threatened by genetic erosion.
Several fractions of Indigofera showed various interesting pharmacological effects, both in vitro and in vivo. Further research is needed to fully evaluate these preliminary results for future applications.
198, 239, 542, 688, 731, 870.
Selection of species
- Sudibyo Supardi & Hurip Pratomo