Enhalus acoroides (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Enhalus acoroides (L.f.) Royle

Protologue: Illustr. bot. Himal. 1: 453 (1840).

Family: Hydrocharitaceae

Chromosome number: 2n= 14

Synonyms

Stratiotes acoroides L.f. (1781), Enhalus koenigi Rich. (1814), E. marinus Griff. (1851).

Vernacular names

• Eel grass, tropical eel grass (En)
• Indonesia: deringu laut (Indonesian), jelamun (Javanese), lamun (Sundanese, Balinese)
• Malaysia: setul, jerangau laut
• Philippines: lamon (Tagalog, Bikol), mariu-bariu (Bikol), pallaipat-baibai (Ilokano).

Origin and geographic distribution

E. acoroides is a marine plant distributed from East Africa, Madagascar and the Seychelles through the tropical parts of the Indian Ocean, the southern part of the Red Sea, and throughout South-East Asian coastal waters to China, northern Australia, Micronesia and Melanesia. It is rare in the Indian Ocean area, but very common in South-East Asia, where it occurs around Thailand, Cambodia, Vietnam, Malaysia, Indonesia, Papua New Guinea and the Philippines.

Uses

The black fibre strands of the leaf margins of E. acoroides persist after the leaves decay and are used for making fishing nets (the Moluccas, New Guinea and Micronesia). They have also been used for mats, ropes and paper making. The raw, boiled or roasted seeds are edible and are sometimes eaten in the Philippines, Indonesia (Java, the Moluccas) and India. In the Philippines the fruits and leaves are chewed or macerated and the mixture is applied to wounds to staunch bleeding, whereas the seeds are credited with aphrodisiac and contraceptive properties. E. acoroides is grazed by turtles and dugongs ( Dugong dugon ).

Production and international trade

In some regions of the Philippines seeds of E. acoroides are sold in local markets, but no statistics are available on production or trade.

Properties

Fishing nets made of E. acoroides are very durable in sea water and tanning is not needed. On Yap (Caroline Islands, Micronesia) the traditional nets used to be used throughout a person's life and were passed on to the next generation. Nets that were not used for some time were protected by being periodically dipped in sea water, dried, and wrapped to protect them against rats and geckos. No information is available on the physical and chemical properties of the fibre.

The raw seed is described as crunchy and sweet, whereas the boiled seed tastes like boiled sweet potato or chestnut. The testa is bitter and should not be eaten. Flour prepared by grinding dried E. acoroides seed from the Philippines contains per 100 g approximately: moisture 10 g, protein 9 g, fat 0.2 g, carbohydrates 72 g, crude fibre 2 g, ash 6 g, Ca 90 mg, P 240 mg and Fe 280 mg. The energy value is about 1370 kJ per 100 g.

Adulterations and substitutes

Substitutes for E. acoroides as a source of fishing nets include Anodendron spp. and ramie ( Boehmeria nivea (L.) Gaudich.).

Description

A perennial, marine, submerged, dioecious, rhizomatous, coarse, glabrous herb. Rhizome creeping, up to 1.5 cm in diameter, inside with wide, septate air channels, outside bearing numerous simple, cord-like roots 10-20 cm × 0.3-0.5 cm and densely clothed with persistent fibrous strands of decayed leaves. Leaves sessile, usually 2-6, distichously arranged at the end of the rhizome, together enclosed by a flattened, transparent sheath about 15 cm long, often twisted and damaged, bright to dark green; blade ribbon-like, 30-150 cm × 1-1.8 cm, base sheathed, margin thickened by coarse, very tough vascular bundles which become black after the blade decays and remain attached to the rhizome, apex rounded or obtuse, veins 13-19, running longitudinally parallel, air channels 30-40, parallel to the veins, visible outside as a fine striping with irregularly spaced septations. Male inflorescence an axillary, peduncled spathe consisting of 2 connate bracts, the margin of the outer one embracing the inner one; peduncle terete, 5-10 cm long; bracts ovate-lanceolate, 5 cm × 3 cm, faintly keeled, rough long-haired on the keel; flowers small, numerous, pedicelled, on a central stipe, caducous just before anthesis and the mature buds rising to the level of the water; pedicel 3-12 mm long, unequal, very thin; sepals 3, oblong, 2 mm long, reflexed, white; petals 3, ovate, wider but slightly shorter than sepals, white; stamens 3, erect, 1.5-1.8 mm long, anthers subsessile, 2-locular, dehiscing latrorsely, pollen grains spherical, about 175 μm in diameter. Female inflorescence a stalked spathe consisting of 2 nearly free bracts, one embracing the other with both margins, persistent in fruit, enclosing 1 flower; stalk (pedicel) 40-50 cm long, spirally contracted after fertilization, in fruit unrolled again; bracts oblong-lanceolate, 4-6 cm × 1-2 cm, strongly keeled, keel and veins rough long-haired; sepals 3, oblong, reddish; petals 3, oblong-linear, 4-5 cm × 0.3-0.4 cm, white, surface waxy and papillose; ovary rostrate, 5 cm × 0.5 cm, densely set with long fringe-like hairs, composed of 6 carpels, 1-locular, ovules numerous; styles 6, very short; stigmas 6, each forked from the base, 10-12 mm long, densely covered with linear papillae. Fruit berry-like, ovoid to subglobose, 5-7 cm in diameter, ribbed lengthwise, densely hairy, green, brown or black, opening irregularly at the apex at maturity, 8-14 seeded. Seed angular-obconoidal, 1-1.5 cm × 1.2 cm, brown.

Growth and development

Both leaf growth and leaf initiation rate of E. acoroides increase with water temperature. Observed leaf growth rates in South-East Asia range from 0.7-3.1 cm per day, with a new leaf being initiated every 27-35 days. The largest part of the plant biomass is located in the subterranean rhizome and roots.

Flowering appears to be year-round. Pollination is effected by the male flowers detaching from the parent plant, floating on the water, and coming into contact with the stigmas of the female flowers (" Hydrocharitaceae epihydrophily"). The male flowers open in the closed spathe and are liberated when the spathe opens, but only when the low spring tide occurs during the day. Pollination requires the female inflorescence to reach the water surface, which only occurs during sufficiently low tides, when the water level is no more than 0.4 m above the seagrass bed. The female flowers on the water surface "attract" the male flowers by the hydrophobic properties of the petals. When the tide rises again the female flowers are submerged, the petals close together, "capturing" the male flowers, and pollination occurs. Fruiting seems to occur year-round as well, though in Papua New Guinea successful fruit formation occurs mainly between April and August. The time from pollination to opening of the fruits varies from 3-5 months in Papua New Guinea. There are indications that fruits open predominantly during spring-ebb tides. When the fruits open, the seeds are already in an early stage of germination. Seeds with the testa loosely attached float on the water, those without testa sink. The seeds are distributed not only by sea water, but also by dugongs.

Algal epiphytes are usually present on the leaves of E. acoroides . In Papua New Guinea they were found to contribute 3-17% to the total aboveground plant biomass and 2-9% to the mean annual aboveground plant production.

Other botanical information

E. acoroides is the only species in Enhalus Richard (1814). The Hydrocharitaceae family comprises species with both freshwater and marine habitats, a rather rare occurrence in angiosperm families. The family comprises about 15 genera, but its delimitation is constantly changing and its floral biology is not fully understood.

Ecology

E. acoroides is found along sheltered or exposed shallow sea-coasts, from around the low-water mark to about 5 m depth. It occurs in a wide range of habitats and thrives in small depressions on tidal flats between the levels of mean low water and low water at spring tide. E. acoroides may occur patchily or form a closed monospecific stand, the latter particularly on sandy and muddy bottoms, often mixed with coarser material. It may grow abundantly in fish ponds, waterways and coastal resorts, and can form an obstruction.

Propagation and planting

E. acoroides can be propagated by seed, but is not planted deliberately. Fibres and seeds are obtained from wild stands.

Husbandry

Experiments in the north-western Philippines have shown that shoot size and leaf growth of E. acoroides are sometimes limited by the availability of nutrients, especially nitrogen.

Harvesting

In Yap, fibres of E. acoroides were traditionally collected at low tide from special, protected marine meadows. First the leaves were pulled up, and debris and epiphytes were stripped off. Then a thumb was inserted in the axil of the chosen leaf which was subsequently separated from the plant. The outermost leaf was usually not picked, because its fibres are generally broken and too stiff to be used. The basal portion of the harvested leaf was grasped in one hand and the central portion of the leaf blade stripped away with the thumb of the other hand, leaving a short section of the leaf blade with long strips of the leaf margin extending on either side.

Yield

In the north-western Philippines E. acoroides produces about 150 seeds/m²per year. No statistics or estimates of the fibre yield are available.

Handling after harvest

In Irian Jaya (Indonesia) the longest fibres are scraped off, dried in the sun, separated and twisted into rope. In Yap, the traditional processing method was to tie the harvested strips in bundles and hang them on poles to dry, after which the fibres were carefully extracted from the surrounding tissue. To extract the fibres, the double strands were held firmly in one hand and the connecting leaf blade was grasped firmly between thumb and forefinger and stripped off, exposing the fibres, from which the remaining leaf tissue was subsequently stripped off. If the leaf tissue became too dry, it was rewetted and dried to the appropriate dryness for fibre extraction. Once extracted, the fibres are stable and can be stored.

In Yap about 4-5 fibres were made into a strand by twisting them with the finger and rolling them on the thigh. Then 2 strands were rolled together to make a twine, to which new strands were added to make the twine longer. The twines were made into nets.

Genetic resources

Because of its wide distribution and range of habitats, E. acoroides seems not to be threatened with extinction, though South-East Asian seagrass ecosystems in general are subject to threats such as heavy deposits of mining spoils, destructive fishing methods, conversion in favour of aquaculture and increased sedimentation due to deforestation. There are no known germplasm collections of E. acoroides .

Prospects

E. acoroides will probably continue to be locally used as a source of fibre for fishing nets. Though the nutritional quality of flour made from the seeds is good, mariculture of E. acoroides is not feasible because of the low yield per area unit.

Literature

• Brouns, J.J.W.M. & Heijs, F.M.L., 1986. Production and biomass of the seagrass Enhalus acoroides (L.f.) Royle and its epiphytes. Aquatic Botany 25(1): 21-45.
• den Hartog, C., 1957. Hydrocharitaceae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Series 1, Vol. 5(4). Noordhoff-Kolff N.V., Djakarta, Indonesia. pp. 381-413.
• den Hartog, C., 1970. The sea-grasses of the world. Verhandelingen der Koninklijke Nederlandse Akademie van Wetenschappen, afd. Natuurkunde. 2nd series, part 59, No 1. North-Holland Publishing Company, Amsterdam, the Netherlands. pp. 214-222.
• Falanruw, M.C., 1992. Seagrass nets. Atoll Research Bulletin No 64. National Museum of Natural History, Smithsonian Institution, Washington, D.C., United States. 12 pp.
• Montaño, M.N.E., Bonifacio, R.S. & Rumbaoa, R.G.O., 1999. Proximate analysis of the flour and starch from Enhalus acoroides (L.f) Royle seeds. Aquatic Botany 65(1-4): 321-325.
• Verheij, E. & Erftemeijer, P.L.A., 1993. Distribution of seagrasses and associated macroalgae in South Sulawesi, Indonesia. Blumea 38(1): 45-64.

Authors

Y. Umi Kalsom