Mimosa pudica (PROSEA)

• Sensitive plant (En).
• Sensitive (Fr).
• Brunei: puteri malu, rumput malu, sopan malu (Malay)
• Indonesia: putri malu (general), jukut riyud (Sundanese), pis kucing (Javanese)
• Malaysia: memalu, malu-malu
• Papua New Guinea: matmat (Gunantuna, New Britain)
• Philippines: makahiya (Tagalog), torog-torog (Bikol), babain (Ilokano)
• Cambodia: smau bânla, bânkrap
• Laos: f'a:z langab, th'üb nhub
• Thailand: ka-ngap (peninsular), maiyaraap (central), yaa pan yot (northern)
• Vietnam: cây mắc cở, cây xấu hổ, cây trinh nữ.

Sensitive plant probably originated in South America but is now pantropical. It occurs commonly throughout South-East Asia, usually along roadsides and on wasteland.

In Indonesia, Malaysia and Thailand, sensitive plant was traditionally used to treat insomnia. Twigs were placed under the sleeping mats of children, and they were also used as a decoction to prepare a bath for children with sleeping problems. This use was probably based on signature: the leaves "go to sleep" in the evening. At the beginning of the 20th Century, twigs were being sold for this purpose in Java, but there is no recent confirmation of this traditional use. In Vietnam, however, the leaves are considered in folk medicine to be sedative and hypnotic, and an infusion of the leaves is still regarded beneficial for patients suffering from insomnia. Test with mice seem to confirm this activity.

Other uses reported are the treatment of haematuria (all parts of the plant, Indonesia and Thailand) and as a poultice to treat swellings (pounded leaves, Indonesia, Malaysia and Thailand). In Brunei, a root decoction is drunk to relieve asthma and diarrhoea. The most extensive use of the plant in South-East Asia is in the Philippines, where a decoction of the entire plant is considered anti-asthmatic and a root decoction is given as a diuretic and also to treat dysmenorrhoea. In Thailand, the whole plant is used as a diuretic. The leaves are used externally to treat dermatitis, wounds and ulcers. The roots are traditionally used in Vietnam to treat arthritis. In India, a root decoction is used to treat urinary complaints and as an aphrodisiac, whereas it is considered emetic in South America and is also used there to treat diarrhoea and dysentery. In India, crushed leaves are applied as an emollient to glandular swellings, and an infusion of the leaves is used in Vietnam to treat febrile stiffness. In New Britain, roots and leaves have been used externally to treat swollen testicles. In Indo-China seeds are considered to be emetic; in India they are also used to treat sore throat and hoarseness. In the traditional pharmacopoeia of La Réunion, the stems, leaves and roots are mentioned as a calming remedy against insomnia, spasms and convulsions of children.

Sensitive plant contains tannins that can be used in the production of leather. Young stems and leaves are useful as forage. When the prickles on the stem and the fruits become too hard, they can cause intestinal inflammation in animals. Moreover, the mimosine present in the plant may cause poisoning. Sensitive plant is often considered as a noxious weed. In areas where other leguminous plants establish with difficulty, it can be of use as a cover crop or green manure. In Thailand, it is used as ground cover on road verges.

Sensitive plant is harvested in small amounts for personal use, and is only very rarely traded.

Sensitive plant contains mimosine (N-(3-alanyl)-3-hydroxy-4-pyridone), an amino acid which is biosynthetically derived from lysine. This compound is reported as being toxic to several animal species, including pigs and rabbits, and to a lesser extent, ruminants such as cattle. Mimosine is reported to have depilatory properties, and prolonged use may lead to alopecia. The intoxication also manifests itself by loss of appetite and weight, and retarded growth. These symptoms are accompanied by an enlargement of the thyroid gland, and lowered serum thyroid hormone levels. Mimosine itself inhibits the synthesis of proteins and nucleic acids, but is not known as a goitrogen. Gut bacteria, however, transform mimosine enzymatically into 3-hydroxy-4(1H)-pyridone (= 3,4-dihydroxypyridine, DHP), which is a potent goitrogen able to cause hypo-thyroidism. Oral application of 1 ml of a DHP solution (0.25 mmol) in the rat has been found to significantly inhibit¹²⁵I uptake by the thyroid gland. Bacteria able to further metabolize DHP into non-goitrogenic compounds have been isolated from the gut of various animals, including Indonesian goats. When these bacteria were transferred into Australian cattle, the cattle were able to feed on mimosine-containing forage without suffering toxicological reactions.

Mimosine has been demonstrated to reversibly block cell cycle progression in mammalian cells in culture. It also, through iron chelation, blocks cell cycle progression in asynchronous human breast cancer cells. In addition to mimosine, two C-glycosylflavones have been isolated from the aerial parts of the plant, and identified as 2-O-rhamnosyl-orientin and 2-O-rhamnosyl-isoorientin.

In Vietnam, a significant hypotensive effect has been reported in experiments with dogs injected with a 10% infusion of leaves. Sedative, anti-inflammatory, anti-implantation and anti-arthritic effects have also been reported. Tests with mice showed prolongation of the time spent sleeping. An alcoholic extract, a petroleum-water extract and quaternary alkaloids isolated from whole dried plants in Thailand lowered blood sugar in diabetic rats, beginning in the second hour after single oral application and reaching a maximum after 6 hours; no abnormal symptoms were observed. The total alkaloidal extract of the roots was found to be antagonistic to both acetylcholine and histamine on isolated guinea-pig ileum. In tests with rats in India extracts were not effective in preventing bladder stone deposition or in dissolving preformed stones. The methanol extract of aerial parts showed diuretic activity and some protection against the injurious effect of radiations.

In tests in Nigeria, the extract exhibited antimicrobial activity against Vibrio cholerae, but the potential in the control of cholera needs to be determined. An in vitro bioassay of an aqueous methanol extract of green leaves in Jamaica showed that the extract inactivated 50% of the filariform larvae of the nematode Strongyloides stercoralis (causing strongyloidiasis) in less than 1 hour. The root extract is also nematicidal. At a concentration of 300 ppm it completely inhibited egg hatch of Meloidogyne incognita, and also significantly affected the infectivity and development of larvae. A crude ethanol extract of the leaves was found to have insecticidal activity against adult Tribolium confusum when sprayed as a 10% concentrate; it killed 60% of the beetles.

Very little is known about the forage quality of sensitive plant. It is likely that the quality of any sample would vary considerably with the leaf/stem ratio.

Mimosine and its optically inactive form leucaenine are also known from Leucaena leucocephala (Lamk) de Wit.

• An annual or perennial herb, sometimes woody at base and then subshrubby, up to 1(-1.5) m tall, often prostrate or straggling; stem usually sparsely armed with recurved prickles up to 5 mm long, glabrous to densely hispid.
• Leaves alternate, bipinnate, unarmed, sensitive; petiole (1.5-)3-5.5 cm long, hispid, rachis very short, giving the two pairs of pinnae a subdigitate position; stipules caducous; leaflets 10-26 pairs per pinna, oblong to subfalcate, 0.6-1.5 cm × 0.1-0.3 cm, margins setulose.
• Inflorescence an axillary globose head, about 1 cm in diameter, 1-2(-5) together per axil; peduncle up to 4 cm long.
• Flowers bisexual, 4-merous, sessile, lilac, pink or blue-purple; calyx inconspicuous, about 0.1 mm long; corolla narrowly campanulate, 2-2.5 mm long, with obtuse to rounded lobes; stamens free, much longer than corolla; ovary superior, glabrous, style long and slender.
• Fruit a flattened oblong pod, 1-1.8 cm × 0.3-0.5 cm, several together in a cluster, densely setose, prickly on margins, consisting of 3-5 1-seeded joints which break away from the persistent sutures.
• Seeds suborbicular to broadly ellipsoidal, flattened, 2.5-3 mm long, pale brown, surface finely granular.
• Seedling with epigeal germination, smelling like garlic; cotyledons ovate, sagitate at base, truncate to emarginate at apex, glabrous; hypocotyl up to 15 mm long, hairy, epicotyl absent; first leaf solitary, with 3 pairs of leaflets.

Sensitive plant flowers throughout the year and it can complete its life cycle in 3 months. The leaves are extremely sensitive to the touch. At nightfall the leaflets fold up and the rachises bend down.

Within the subfamily Mimosoideae, Mimosa is classified in the tribe Mimoseae. It is a large genus of about 400 species mainly occurring in tropical America.

Four varieties of M. pudica are distinguished: var. pudica (only known from the sterile type specimen, no distinction possible); var. hispida Brenan (corolla in bud densely grey puberulous; heads in bud densely bristly; stipules 8-14 mm long); var. tetrandra (Humb. & Bonpl. ex Willd.) DC., synonym: Mimosa tetrandra Humb. & Bonpl. ex Willd. (corolla in bud densely grey puberulous; heads in bud sometimes sparsely bristly; stipules 4-8 mm long); var. unijuga (Duchass. & Walp.) Griseb., synonym: Mimosa unijuga Duchass. & Walp. (corolla in bud glabrous; heads in bud not bristly; stipules 4-8 mm long). The three latter varieties are all pantropical and occur throughout South-East Asia.

Sensitive plant is common in wasteland, disturbed areas and overgrazed sites with moderately to poorly fertile soils. It occurs in the humid tropics and tolerates waterlogging but is not well adapted to the seasonally dry tropics. In the Malesian region, sensitive plant is found up to 1000 m altitude. It is regarded as a weed in upland field crops, in rainfed wetland rice and in plantation crops where it is reasonably tolerant of shade. It occurs over a wide range of soils, but iron chlorosis has been noted on coralline soils with a high pH.

The persistence and spread of sensitive plant is aided by its prolific seed set. There are approximately 110 seeds/g.

Sensitive plant is not sown deliberately, nor is its establishment or spread promoted. On the contrary, it is usually regarded as a noxious weed. It tends to invade pastures of declining soil fertility and is less common where soil fertility is good and pastures are not overgrazed. Sensitive plant has been eliminated from pastures where soil fertility is very poor and grazing pressure is very high. It grows with a wide range of grasses, including signal grass (Brachiaria decumbens Stapf) provided that grass is not too vigorous. It can hamper the establishment of improved species. Sensitive plant is more readily accepted if it is grazed continuously rather than rotationally. Observations suggest that it may at times stimulate growth of associated grasses.

M. pudica plants in Bogor (Indonesia) are often found attacked by a fungus (Ramularia mimosae) which grows on the upper surface of the leaflets, forming irregular white spots. This fungus originates from tropical America and is also reported on M. pudica in India.

Sensitive plant is harvested from populations in the wild.

In the Philippines, harvested plants intended for preparing an ointment or cream for external use against skin complaints are air dried, cut into small pieces and ground in a grinding machine. The powdered plant is subsequently submerged in 80% ethyl alcohol, and the mixture heated for one hour. The extract obtained is a yellowish-green syrupy substance with a bitter taste. Powdered dried roots should be stored in airtight containers, preferably in sterilized bottles.

Being a common weed, sensitive plant is not at risk of genetic erosion. There are no known germplasm collections of sensitive plant, nor breeding programmes.

Very little research has been done on the medicinal properties of sensitive plant. The scarce information from research suggests interesting possibilities as an anti-microbial, nematicidal and insecticidal agent, but the true value of the plant should be established by further investigations. Other attributed properties, such as the sedative activity, seem to have some scientific basis, but the indications are still vague.

Although sensitive plant can provide useful forage, it will continue to be primarily regarded as a weed. Although more appropriate management may promote its use, it would be preferable to grow forages that are more readily accepted by grazing animals or more suited to cut-and-carry feeding systems.

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• Erlin Rachman