47

8: Vegetables

Neptunia oleracea Loureiro

Flora Cochinchinensis: 654 (1790).

LEGUMINOSAE

2n = 56

Neptunia prostrata (Lamk) Baillon (1883), Neptunia natans (L.f.) Druce (1917).

Water mimosa (En). Neptunie potagère (Fr). Indonesia: kemon (Lampung). Malaysia: keman air, keman gajah, tangki. Cambodia: kânhchhnaèt. Laos: ('phak) kas'ééd. Thailand: phakkrachet (central), phakchit (peninsular). Vietnam: rau nh[us]t (South), rau r[us]t (North).

Water mimosa is widely distributed in the tropics of both hemispheres. The origin of the species is uncertain. It occurs wild and cultivated as a vegetable throughout South-East Asia, particularly in Thailand and Indo-China.

Water mimosa is mainly gathered and cultivated for its young shoots, which are consumed as a vegetable, raw, cooked, or fried. It is a common ingredient of Thai cuisine. The people of Kelantan (Malaysia) use the root as an external remedy for necrosis of the bones of the nose and hard palate. The juice of the stem is squeezed into the ear to cure earache and the root is used in the advanced stage of syphilis in Malaysia.

Water mimosa is only locally grown and is marketed on a small scale. No data on production and trade are available.

Per 100 g edible portion the shoots contain: moisture 89.4 g, protein 6.4 g, fat 0.4 g, carbohydrates 0.8 g, fibre 1.8 g, ash 1.2 g, Ca 387 mg, P 7 mg, Fe 5.3 mg, vitamin A 5155 IU, vitamin B1 0.12 mg, vitamin B2 0.14 mg, niacin 3.2 mg and vitamin C 1.8 mg. The energy value is 134 kJ/100 g.

Perennial herb, sometimes grown as an annual, aquatic, floating or prostrate near water's edge. Taproot thick, becoming woody. Stems terete up to 1.5 m long, rarely branched, becoming detached from the primary root system, forming spongy-fibrous swollen internodes (to float) and producing fibrous adventitious roots at the nodes when growing in water. Leaves alternate, bipinnate, with 2-3(-4) pairs of pinnae; petiole angled, 2-7 cm long; rachis 3.5-8 cm long, angled; rachis of pinnae winged, 2.5-6.5 cm long; leaflets 8-20 pairs per pinna, oblong, 5-18 mm x 1.5-3.5 mm, asymmetrical, glabrous or with sparsely ciliate margins. Inflorescence an axillary, erect or slightly nodding solitary spike which is obovoid in bud, 30-50-flowered; peduncle 5-30 cm long; flowers small, sessile, yellow, lower ones sterile, upper ones bisexual. Bisexual flowers with campanulate calyx of 2-3 mm and 5-lobed; corolla with 5 regular petals, free, 3-4.5 mm long; stamens 10, free, 6-9 mm long; pistil up to 9 mm long, usually exserted beyond the stamens. Fruit a legume, broadly oblongoid and flat, 2-3 cm x 1 cm, dehiscent along both sutures; fruit stalk longer than the persistent calyx. Seeds 4-8, compressed ovoid, 4-5 mm x 2.5-3.5 mm, brown.
In Thailand, water mimosa is usually grown at the beginning of the rainy season (May). Under favourable conditions young shoots may elongate at a rate of 5-7 cm per day. The plants start to flower during the dry season (December). Its cropping period is 4-6 months.

Water mimosa is a common floating plant in and around fresh water ponds, swamps and canals at low altitudes up to 300 m. When the water level falls, the plants perish. The rooted land form has smaller leaves and flowers, and has no spongy floating tissue. The plant prefers 30-80 cm depth of slow-moving water, full sun and hot and humid conditions. Shade, brackish water and saline soil adversely affect plant growth.

Water mimosa can be propagated by seed, but the conventional method is by stem cuttings. Two cultivation methods are practised in Thailand: in inundated fields normally used for rice, and in canals. In the case of rice fields the land is levelled and ploughed in the same way as for transplanted rice. The plot is filled with water to a depth of 20-30 cm, and 3-5 stem cuttings, 50-150 cm long are directly planted at a spacing of 1 m x 2 m. One week after planting, the water level is raised and kept at 50 cm. When growing in canals where the depth exceeds 50 cm, stakes are needed to hold the floating cuttings in place.
Aquatic weeds, such as Pistia stratiotes L., Eichhornia crassipes (Martius) Solms, Lemna spp., and Ludwigia adscendens (L.) Hara, must be regularly cleared from the water. When grown in rice fields, application of 150-300 kg/ha of a mixed N and P fertilizer is recommended. This amount is given in split doses, the first at planting, subsequent ones after each harvest during the rainy season. The water level should be lowered to 20-30 cm depth before each fertilizer application, and raised up to 50 cm depth two days later. No fertilizer is applied when water mimosa is grown in canals.
The first harvest can be done 3-4 weeks after planting and subsequently at intervals of 5-7 days during the 4-6 months cropping season. Young shoots of 50-100 cm length are cut with a sharp knife and washed. They may be disinfected by dipping in a dilute alum solution for a few minutes. The spongy tissue may be removed by keeping the plants under water for about one week, but this treatment is not commonly practised. Bundles of 250 shoots are wrapped in plastic film and sent to the markets for sale in smaller bundles. A yield of 30 000-50 000 shoots/ha for each harvest has been reported.
No disease has yet been recorded, and very few pests attack water mimosa. The larvae of the leaf roller Synclita sp. may attack the spongy tissue and stem. Synthetic pyrethroid insecticides are recommended for the control of this insect. Plant-eating fishes, turtles, ducks and geese are found to feed on water mimosa.

Only local selections are grown. No work has been undertaken on germplasm collection and breeding.

Water mimosa is a nutritious and productive vegetable. Research should focus on the selection of productive and marketable types, and improvement of cultivation methods.

Division of Food Science, 1981. Nutritional value of Thai foods. Ministry of Public Health, Bangkok, Thailand. 16 pp.
Nielsen, I.C., 1985. Leguminosae - Mimosoideae. In: Smitinand, T. & Larsen, K. (Editors): Flora of Thailand. Vol. 4(2). The Forest Herbarium, Royal Forest Department, Bangkok, Thailand. pp. 146-149.
Saengtham, C., 1987. Khlong phakkrachet haeng lumnam nakhonchaisri [Water mimosa]. Thankasettakam [Agricultural Base Journal] 5(50): 25-30.
Tanphiphat, S., 1985. Phak-krachet watchaphuet thimi khunnakha [Water mimosa]. Warasarn kaset phrachomklao [King Mongkut's Agricultural Journal] 3(2): 29-39.
Windler, D.R., 1966. A revision of the genus Neptunia (Leguminosae). Australian Journal of Botany 14: 379-420.

Y. Paisooksantivatana

Paisooksantivatana, Y., 1993. Neptunia oleracea Loureiro. In: Siemonsma, J.S. and Piluek, K. (Editors): Plant Resources of South-East Asia No 8: Vegetables. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea