Crotalaria juncea, Sunn hemp, brown hemp, Indian hemp, Madras hemp

Crotalaria juncea, popularly known as Sunn hemp, brown hemp, Indian hemp or Madras hemp is a tropical Asian plant of the legume family (Fabaceae).  The plant is generally considered to have originated from Asia especially Asia tropical (Bangladesh; Bhutan; India). It is now widely cultivated in the drier areas of the tropics and subtropics and in many temperate areas with a hot summer. It is recorded in many countries across the African continent from the Atlantic coast to the Red Sea, from Tunisia to South Africa and in the Indian Ocean islands. The plant has got several common names including brown hemp, Bumpo, Ghore sun, Indian hemp, Janumu, Madras hemp, Oohawaimaton, San, Sana, Sanabu, Sanai, Sanal, Sann hemp, Sannai sunn, Sannappu, Saun, Senabina soppu, Shon, Shonpat, Sunn hemp, Tag, Tum-thang, Wuckoo nar, Benares hemp, Bengal hemp, Bombay hemp, Brown hemp, Jubbalpore hemp, Sun hemp, Sann hermp, sunn Crotalaria, Cascavelle, Cocosnut, Grand Sonnette, Grand Tcha-Tcha and Sonnette.

The genus name Crotalaria means rattle and is indicative of the noise made by the seeds shaken in the mature pods. The species name juncea was given to this plant by Linnaeus because of its resemblance to Spartium junceaum L., the Spanish broom of the Mediterranean region with its green rush like, scantily-leaved branches. Crotalaria juncea is the fastest growing and most important species of the Crotalaria genus. Sunn hemp is not related to industrial hemp or marijuana. It is actually in the genus Crotalaria but it is not toxic to livestock like Crotalaria spectabilis. The plant is considered as a source of green manure, fodder and lignified fiber obtained from its stem. Sunn hemp is also being looked at as a possible bio-fuel. It can be an invasive weed and has been listed as a noxious weed in some jurisdictions.

Plant Description

Sunn hemp is a multipurpose, short-day, annual, erect shrubby, tropical, and subtropical legume that grows about 1 to 4 m tall. The plant is found growing in scrub jungles, dry deciduous forests, and sparse forests and along trails. The plant grows best on fairly light-textured soil like sandy loam or loam of at least moderate fertility. It also grows well on clay soils and will tolerate low fertility providing that soils are well-drained. The plant has a well-developed, long, strong taproot with lateral roots, and much-branched and lobed nodules, up to 2.5 cm in length. The stem is up to 2 cm in diameter, cylindrical, and ribbed with short-appressed hairs.

Leaves

Leaves are simple, about 2.5-10.5 cm long, and 6–20 mm broad, linear or oblong, obtuse or sub-acute?, apiculate, pubescent on both sides, hairs appressed and silky. Leaf-stalk is about 1.2-2.5 mm long. Stipules are almost absent.

Flowers are bisexual, zygomorphic, and 5-merous. Calyx is 1.5–2 cm long, covered in short brown hairs with some longer ones interspersed, lobes 3–4 times as long as the tube.  Corolla is bright yellow; with elliptical standard faintly reddish marked or tinged wings a little shorter than keel. Keel is 17–22 mm long, with a long, slightly incurved twisted beak; stamens 10, all joined in a sheath open at base. Ovary is superior, 1-celled, style curved and small stigma.  Flowering normally takes place from May to September.

Fruits

Fertile flowers are followed by cylindrical hairy pod that is 3-6 cm long and 1-2 cm in diameter, short, velvety hairy and about 6–12-seeded. They are green when young turning to light brown as they matures. Seeds are small flattened, oblique, cordiform, 6-7 mm long, heart-shaped, grayish olive, dark grey or dark brown to black and loosened in the pod at maturity.

Traditional uses and benefits of Sun hemp

• Seeds are believed to purify the blood and are used in the treatment of impetigo and psoriasis.
• It is traditionally used as a blood purifier, abortifacient, astringent, demulcent, emetic, and purgative, in the treatment of anemia?, impetigo, menorrhagia, and psoriasis.
• Infusion of bitter leaves is used externally and internally for gastric and bilious fevers accompanied by skin diseases like impetigo and psoriasis.
• It is also used as an emmenagogue.
• The root is used for colic and as astringent in epistaxis.
• Seeds are used to purify the blood.
• Powdered seeds, mixed with oil are used to make the hair grow.
• In India, it is used for anemia?, impetigo, menorrhagia, psoriasis.

Culinary Uses

• Leaves have been recorded as being eaten.
• Flowers are pickled.
• They are also cooked with meat and fish.

Other Facts

• Bark yields fiber used in making twine and cord, canvas and fishing nets, and paper and pulp.
• Fiber possesses properties that make it an excellent choice for papermaking.
• Fibers are mainly suitable for cigarette paper because of the high cellulose and low ash content.
• The strong bast fiber is used primarily for cordage, twine, fishing nets, cigarette paper, tissue paper, bags, sacks, canvas, soles of shoes and sandals.
• Other products include carpets, webbing, table and bed linen.
• With the fibers a potting medium is manufactured.
• Dried stalks and hay are used as forage.
• Sunn hemp is locally used as fodder.
• The number of seeds/kg is highly variable, ranging from 18,000 to 35,000.
• Valuable, high-quality, strong fiber is extracted from the stems and bark.
• It is often planted for increasing soil organic matter to over-farmed soils, for loosening subsoil, to reduce soil erosion, conserve soil water and recycle plant nutrients.
• It has also been grown in Brazil and Bangladesh as a soil-improving crop.
• It is also grown to suppress weeds, to prevent soil erosion, and to reduce nematode numbers.
• It is a good indicator plant for potassium and calcium deficiencies.
• Seeds are fed to horses in the Soviet Union and to pigs in Zimbabwe.
• Woody stems remaining after fiber removal is used as fuel.
• Seeds are used in the production of an adhesive for plywood and as a coffee-substitute.

Precautions

• Seeds of many Crotalaria species contain toxic pyrrolizidine alkaloids.
• Trichodesmine is the principal toxic alkaloid in Crotalaria juncea.
• Seeds are reported to contain trypsin inhibitors; they are said to be poisonous to cattle, and they can poison both horses and pigs.
• Avoid use during Pregnant and Breastfeeding.

References