Enhalus acoroides (L.f.) Royle
Family
Hydrocharitaceae
Synonyms
Stratiotes acoroides L.f., Enhalus koenigi Rich., Enhalus marinus Griff.
Vernacular Names
|
Malaysia |
Setul, jerangau laut. |
|
Brunei |
Eel grass, tropical eel grass. |
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Indonesia |
Deringu laut (Indonesian), jelamun (Javanese), lamun (Sundanese, Balinese). |
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Philippines |
Lamon (Tagalog, Bikol), mariu-bariu (Bikol), pallaipatbaibai (Ilokano). |
Geographical Distributions
Enhalus 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 Southeast Asian coastal waters to China, northern Australia, Micronesia and Melanesia. It is rare in the Indian Ocean area, but very common in Southeast Asia, where it occurs around Thailand, Cambodia, Vietnam, Malaysia, Indonesia, Papua New Guinea and the Philippines.
Description
Enhalus acoroides is a perennial, marine, submerged, dioecious, rhizomatous, coarse and hairless herb. It is a creeping rhizome, measures up to 1.5 cm in diametre, with wide and septate air channels inside, while at the outside, it bears numerous simple and cord-like roots, measuring 10-20 cm x 0.3-0.5 cm and densely clothed with persistent fibrous strands of decayed leaves.
There are usually 2-6 leaves which are sessile, arranged distichously at the end of the rhizome and enclosed by a flattened, transparent sheath about 15 cm long and often twisted and damaged. The blade is ribbon-like, measuring 30-150 cm x 1-1.8 cm, with sheathed base, thickened by coarse margin, with very tough vascular bundles which become black after the blade decays and remain attached to the rhizome. The apex is rounded or obtuse, and with 13-19 veins. It runs longitudinally parallel, with 30-40 air channels and parallel to the veins. It is visible outside as a fine striping with irregularly spaced septations.
The male inflorescence is an axillary, spathe peduncled consists of 2 connate bracts. The margin of the outer one embraces the inner one. The peduncle is 5-10 cm long and cylindrical. The bracts are ovate-Iance-shaped, measuring 5 cm x 3 cm, faintly keeled and rough long-haired on the keel. The flowers are small, numerous, with stalk on a central stipe and caducous just before anthesis while the mature buds rise to the level of the water. The pedicel is 3-12 mm long, unequal and very thin. There are 3 sepals which are oblong, measure 2 mm long reflexed and white. There are 3 petals which are ovate, and wider but slightly shorter than sepals. They are white. There are 3 erect stamens which are 1.5-1.8 mm long, with subsessile anthers, 2-locular, with spherical pollen grains and measure about 175 µm in diameter. The female inflorescence is a stalked spathe consists of 2 nearly free bracts where one embraces the other with both margins, persistent in fruit and enclosing 1 flower. The stalk (pedicel) is 40-50 cm long and spirally contracted after fertilization. The bracts are oblong-Ianceolate, measuring 4-6 cm x 1-2 cm and strongly keeled. The keel and veins are rough long-haired. The 3 sepals are oblong and reddish. There are 3 petals which are oblong-linear, measuring 4-5 cm x 0.3-0.4 cm, white, with waxy surface and papillose.
The ovary is rostrate, measuring 5 cm x 0.5 cm, densely set with long fringe-like hairs, composed of 6 carpels, 1-locular and with numerous ovules. There are 6 very short styles. There are 6 stigmas where each forks from the base. They are 10-12 mm long and densely covered with linear papillae. The 8-14 seeded fruit is berry-like, ovoid to nearly spherical, measures 5-7 cm in diametre, lengthwise ribbed, densely hairy, green, brown or black and opens irregularly at the apex at its maturity. The seed is brown, angular-obconoidal, measuring 1-1.5 cm x 1.2 cm.
Ecology / Cultivation
Enhalus 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 materials. It may grow abundantly in fish ponds, waterways and coastal resorts, and can form an obstruction.
Line Drawing / Photograph
References
- Plant Resources of South-East Asia No.17: Fibre plants.
