Mucuna (PROSEA)
Introduction |
Mucuna Adanson
- Protologue: Fam. pl. 2: 325 (1763).
- Family: Leguminosae
- Chromosome number: x= 11; M. pruriens: 2n= 20, 22, 24
Origin and geographic distribution
Mucuna comprises about 100 species in the tropics and subtropics of both hemispheres. A few species are widespread, partly as a result of human activities, but far more species have a very limited distribution. In the region covered by Thailand, Indo-China and Peninsular Malaysia 13 species occur, in Java 5 and in the Philippines 13, whereas 11 species are found in the islands of the Pacific Ocean.
Uses
Traditional medicinal uses of Mucuna have been recorded throughout the tropics, but are in general limited. Seeds are used as an aphrodisiac and purgative, and to treat Parkinson’s disease, roots as a tonic, leaves to treat fever and headache, bark against rheumatic complaints, and sap to heal wounds and cuts, and to treat fever. The irritant hairs on the outside of the fruits of various Mucuna species (e.g. M. gigantea) are mentioned as being used in criminal poisoning, whereas apparently minor doses are credited as a vermifuge of very doubtful quality. M. pruriens is widely grown as a cover crop and green manure.
In Java the seeds of M. macrophylla Miq. (synonym: M. junghuhniana (O. Kuntze) Prain) are made into bead chains regarded as charms, to ward off diseases in children. The seeds are also included in a prescription for flatulence.
Properties
The use of M. pruriens seeds for the symptomatic treatment of Parkinson’s disease as supported by modern research is closely linked to the high concentration of the amino acid L-dopa (levodopa; L-3,4-dihydroxyphenylalanine), which stimulates the formation of the neuro-transmitter dopamine in the brain. Dopamine lessens tremors experienced in Parkinson’s disease. However, opinions differ on the side effects and efficacy in the long run of L-dopa. The L-dopa content in M. pruriens seeds collected in Java is not related to their cultivation status and ranges from 1.6-2.8%. Neither is it correlated to the presence of violently itching hairs predominating in wild forms. M. macrophylla, M. gigantea and M. diabolica Backer ex Keuch. yielded L-dopa at concentrations of 1.6-1.9%, 1.7-2.0% and 2.2-2.3%, respectively.
A seed extract of M. pruriens showed in-vivo prophylactic protection against snake (Echis carinatus) venom in mice. In-vitro tests on human plasma and bovine prothrombin revealed that the extract activated prothrombin. Main cause of death after the bite of Echis carinatus is haemorrhage and this could be partially counteracted by the increase in procoagulant activity as observed in vitro.
An ethanol extract of M. pruriens exhibited antipyretic and analgesic activity in rats when given intragastrically at a dose of 1 g/kg. A leaf decoction decreased blood cholesterol and lipid levels. It has been recorded that M. pruriens increases sperm count and motility.
Botany
- Large lianas, sometimes annual or short-lived perennial climbers, rarely erect shrubs.
- Leaves alternate, pinnately trifoliolate; stipules caducous; lateral leaflets variably asymmetrical; stipels often caducous.
- Inflorescence axillary on leafy shoots or on old branches, subumbellate, condensed-paniculate or falsely racemose; bracts and bracteoles caducous.
- Flowers bisexual, showy; calyx 4-5-lobed, 2-lipped with upper pair of lobes connate; corolla papilionaceous, standard rounded with a median claw and a pair of inflexed lateral auricles at base, wings and keel usually much longer, clawed and with small auricle; stamens 10, 9 fused and 1 free; ovary superior, 1-celled, style long, filiform, bent.
- Fruit an ovoid, oblong or linear pod, valves thick, often ribbed or ornamented with raised lamellae and frequently with irritant bristles, septate or apparently so between the seeds, usually dehiscent.
- Seeds discoid to globose or oblong, compressed, hilum usually extending around three quarters of the circumference, but sometimes short and surrounded by a rim-aril.
- Seedling with hypogeal germination; first leaves scale-like or simple.
Seedlings of M. gigantea and M. macrophylla may attain a height of more than 1 m in 3 weeks time. Nodulating ability is reported for numerous Mucuna species. Seeds of M. gigantea can be dispersed by sea currents.
Mucuna is divided into 2 subgenera. Most species belong to subgenus Mucuna, having a woody habit and large, discoid seeds with hilum extending around three quarters of the circumference, whereas a few (e.g. M. pruriens) belong to subgenus Stizolobium, being an annual or short-lived, hardly woody perennial with oblong-ovoid seeds having a very short hilum surrounded by a rim-aril. An overall revision of Mucuna for South-East Asia is still lacking and an up-to-date account for Indonesia and Papua New Guinea is badly needed in view of the great number of endemics recorded in the literature for these countries.
Ecology
Mucuna can be found on a wide range of soils in habitats as diverse as coral beaches, coastal swamps, riverine forest, moist evergreen rain forest, dry thickets, limestone cliffs and open country, from sea-level up to well over 2000 m altitude.
Management
Propagation of M. pruriens (velvet bean) is mostly by seed. Seed requires no scarification, but dry seed requires soaking in water for 24 hours. The germination rate of fresh seed is up to 100%, and seed stored in a cool, dry place may remain viable for 2 years. After sowing, velvet bean requires 1-2 weedings. It is little affected by diseases and pests. Seed yields can be as high as 1500 kg/ha on good soils. Cell suspension cultures of M. pruriens were able to endogenously accumulate L-dopa up to 6% on a dry weight basis.
Genetic resources
In view of their wide distribution and presence in forest margins and secondary regrowth, the Mucuna species treated here do not appear to be threatened by genetic erosion. Germplasm collections of Mucuna are maintained, for instance at Bogor (Indonesia) where there are 55 accessions of M. pruriens, and at Laguna (the Philippines) where there are 29 accessions of Mucuna spp.
Prospects
Research on the phytochemistry and pharmacological properties of Mucuna has led to important discoveries, such as the presence and activities of L-dopa, which is still important in the therapy for Parkinson’s disease. More research may reveal other interesting medicinal properties, which was recently the case concerning activity against the effects of snakebites.
Literature
35, 239, 297, 731, 751, 819, 997, 1000.
Selection of species
Authors
- K.R. Dahal & J.L.C.H. van Valkenburg