3161

15(2): Cryptogams: Ferns and fern allies

Acrostichum aureum L.

Sp. pl.: 1069 (1753).

PTERIDACEAE

2n = 60 (diploid), 120 (tetraploid)

Chrysodium vulgare Fée (1845), Chrysodium aureum (L.) Mett. (1856).

Leather fern, golden mangrove fern (En). Indonesia: paku laut (general), paku cai (Sundanese), krakas (Javanese). Malaysia: piai raya, paku piai, larat. Philippines: lagolo, pakong-laut, pagaypay. Thailand: prong thale (general), pee-yo (Malay-Satun). Vietnam: r[as]ng d[aj]i, c[aa]y r[as]ng.

Acrostichum aureum is pantropical, occurring along the coasts of Asia, America and Africa. It is abundant in mangrove vegetation all over South-East Asia.

In Malaysia, Indonesia (Kalimantan, northern Sulawesi, Kangean and Timor) and the Philippines, young shoots of Acrostichum aureum are eaten as a vegetable. In Vietnam and the Pacific, the firm, dried, parchment-like leaves are stitched together and used as thatching material in the place of straw-thatch. In this way the roof lasts longer and there is much less risk of fire. Should the roof catch fire the leaves burn rapidly and leave very little ash, thus reducing the risk of the rest of the habitation and its furniture catching fire. Medicinally, the pounded or grated leaves and rhizomes are applied as a paste to wounds, ulcers and boils all over South-East Asia. In China the rhizome is used against worms. Acrostichum aureum also has potential as an ornamental because of its handsome leathery leaves and the plant can be grown in pots.

Acrostichum aureum is neither cultivated commercially nor traded internationally. The fern is collected from the wild and is commonly sold on local markets for vegetable or medicinal use. In Vietnam leaves are locally traded as roof material.

In the aboveground parts of Acrostichum aureum the following compounds have been found: amygdalin, arbutin, formic acid, oxalic acid, tannin and saponin. Acrostichum aureum spores are potential causative agents for patients with allergenic rhinitis. In a fertility test in female albino rats, ethanolic and acetone extracts of Acrostichum aureum showed 60—70% anti-implantation activity.

Large fern (up to 4 m tall) with leathery leaves, rhizomes often forming tussocks in mangrove swamps. Rhizome erect to procumbent, up to 6 mm in diameter, amply scaly at the apex; scales linear to lanceolate to broadly ovate near the petiole base, (0.5—)1—2(—4) cm x 0.8 cm, attenuate, margin entire or erose, lustrous brown or bicolorous pale with a blackish central stripe. Leaves tufted, erect or arching, up to 4 m long; petiole up to 1 m long, at the base up to 20 mm in diameter, lustrous, stramineous to grey-brown, glabrous, bearing on upper portion small spine-like remains of reduced glandular pinnae; lamina pinnate, narrowly oblong to elliptical, up to 3 m long, subcoriaceous to coriaceous, glabrous, bright red when young; sterile pinnae simple, ascending, stalk up to 2.5 cm long, lamina narrowly oblong, 8—50 cm x 1—7 cm, base cuneate to rounded and more or less unequal, margin entire, cartilaginous, apex rounded to obtuse and shortly mucronate; midrib grooved above, distinctly raised below; veins raised below, hardly visible on upper surface, close, forming somewhat regularly arranged areoles up to 2 mm x 0.5 mm. Fertile pinnae only on upper portion, like the sterile ones but smaller, 10—15 cm x 1—2.5 cm; sporangia covering the whole underside surface of pinnae except for the midrib; paraphyses minute, capitate, with small multi-lobed apical cells, deep castaneous. Spores trilete, anisopolar with radiosymmetry, rounded triangular, subtriangular or triquete, 40—50(—70) µm x 32—40(—52) µm, the side concave or convex, the angle rounded, the proximal pole flat or conical, the distal pole subhemispherical.

Acrostichum aureum often grows in terrestrial clusters in a tidal water environment with salinity of 0—13 parts per thousand. Individual growth of Acrostichum aureum in its natural habitat shows that there is an increase of coverage when it grows farther inland. Like other mangrove plants they transpire freely and stomata occupy 30% of the lower surface. It prefers open areas; its growth is inhibited under a dense mangrove forest canopy, but where there is a dense Acrostichum aureum cover, mangrove forest recovers badly. In mangrove reforestation programmes, Acrostichum aureum can be a noxious weed.

Acrostichum aureum may be confused with Acrostichum speciosum Willd. Acrostichum speciosum, however, can be distinguished by its smaller size (up to 1.5 m tall), its brownish-green young leaves, its acuminate sterile pinnae, and the dark brown lower surface of fertile pinnae. In the Bogor Botanical Garden (Indonesia), Acrostichum speciosum has been grown successfully in fresh water for more than 10 years. There are 3 species in the genus, the third one (Acrostichum daneifolium Langsd. & Fischer) is neotropical. Acrostichum L. is also classified as belonging to the family Adiantaceae.

Acrostichum aureum is a facultative halophyte, commonly found in coastal areas, in open mud flats in brackish swamps, in disturbed or clear cut mangrove forests and along tidal streams. In Muara Pasir, East Kalimantan (Indonesia) it tends to be a noxious weed in the mangrove forest, which is dominated by Avicennia officinalis L. Dense growth of Acrostichum aureum interferes with the natural regeneration of mangrove species. Acrostichum aureum does not tolerate as much inundation by sea-water as does Acrostichum speciosum; it prefers the drier parts of the mangrove areas and it continues to grow inland, surviving also in fresh water at altitudes up to 100(—300) m. There is one extraordinary record of Acrostichum aureum growing at 550 m, 400 km inland on highly saline, mineral rich soil next to hot springs. Young plants are often found in sheltered locations on rocky shores, but in such positions they rarely attain any size.

Natural propagation and regeneration of Acrostichum aureum is by spores. Vegetative propagation is possible by clump division and by rhizome cuttings.

Acrostichum aureum is not cultivated commercially. Large plants are generally intolerant of disturbance, whereas small specimens will adapt to cultivation readily. Full sunlight and plenty of moisture are required throughout its growth. It is also possible to grow Acrostichum aureum in pots. A recommended potting mix is a ratio of 1-1-2 of vegetable mould, sand and leaf mould respectively with pH 5.5—6.5.

No germplasm collections nor breeding programmes are known to exist for Acrostichum aureum. Because it is a pantropical fern species, often occurring as a weed, there is up to now no danger of extinction.

Acrostichum aureum has proved to be useful as a vegetable, for roofing and in traditional medicine. The natural habitats of this fern are facing serious destruction due to the accelerated exploitation of mangrove areas for timber and firewood or conversion of the land for other purposes. Further research towards its domestication, as a means for its conservation, deserves more attention.

Amoroso, V.B., 1990. Ten edible economic ferns of Mindanao. The Philippine Journal of Science 119 (4): 295-313.
Bunnag, C., Dhorranintra, B., Limsuvan, S. & Jareoncharsri, P., 1989. Ferns and their allergenic importance: skin and nasal provocation tests to fern spore extract in allergic and non-allergic patients. Annals of Allergy 62(6): 554-558.
Holttum, R.E., 1966. A revised flora of Malaya. 2nd Edition. Vol. 2. Ferns of Malaya. Government Printing Office, Singapore. pp. 409-410.
Prakash, A.O., Saxena, V., Shukla, S., Tewari, R.K., Mathur, S., Gupta, A., Sharma, S. & Mathur, R., 1985. Anti-implantation activity of some indigenous plants in rats. Acta Europaea Fertilitatis 16(6): 441-448.
Sukardjo, S., 1988. Komunitas Acrostichum aureum L. di hutan mangove Avicennia officinalis L. Muara Pasir, Sungai Kandilo, Kalimantan Timur [Community of Acrostichum aureum L. in the Avicennia officinalis L. mangrove forest of Muara Pasir, Sungai Kandilo, East Kalimantan]. Rimba Indonesia 22 (1-2): 59-74.

Dedy Darnaedi & Titien Ngatinem Praptosuwiryo

Darnaedi, D. & Ngatinem-Praptosuwiryo, T., 2003. Acrostichum aureum L.. In: de Winter, W.P. and Amoroso, V.B. (Editors): Plant Resources of South-East Asia No 15(2): Cryptogams: Ferns and fern allies. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea