Articles

Enhalus acoroides (L.f.) Royle

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.

Indonesia     

Deringu laut (Indonesian), jela­mun (Javanese), lamun (Sundanese, Balinese).

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

Enhalus_acoroides

References

  1. Plant Resources of South-East Asia No.17: Fibre plants.