Mangrove fern (Acrostichum aureum), is a large understory fern that occurs in mangrove forests and other wetlands. Plants measure approximately 1.2 - 1.8m (4 - 6 feet) in height and are as broad as they are tall. Fronds are usually arching around the periphery of the plant, but tend to be more erect near the center. The thick, leathery leaves are compound and large, measuring over 1m (3.3 feet) in length, and 12 - 50 cm (4.8 - 19.7 inches) in width. There are 24 - 30 pairs of alternate leaflets (pinnae) that are non-overlapping, rounded at the tips, and measure approximately 10 - 34 cm (3.9 - 13.3 inches) in length X 1.3 - 7 cm (0.5 - 2.8 inches) in width. Leaves are shiny and typically dark green above, but paler on the leaf underside. Leaf margins are somewhat uneven and wavy in appearance.
No sori are present as in other ferns. Rather, sporangia are distributed over the entire underside of reproductive pinnae (the most distal 5 or more pairs), lending a felt-like texture to these leaves. Sporangia are brick red to rust red in color, with spores measuring 37 - 72 µm in diameter.
Distribution: Pantropical in distribution, occurring along the coasts of Asia, America and Africa. A common species in mangrove areas.
Mangrove Fern's Behavior & Ecology
Mangrove fern inhabit neotropical mangrove swamps, salt marshes, low hammocks, and canal margins. In many parts of the World, they have been considered a vegetative pest that interferes with growth and regeneration of mangrove trees.
Mangrove fern grows well in nearly all light conditions, from full sun to dense shade. Maximum rates of productivity, development, and reproductive capacity are observed under full sun exposure; however, Acrostichum aureum is highly shade-tolerant and takes advantage of decreased evaporative rates in shade to reduce salt stress in estuarine environments.
Mangrove Fern's Reproduction
Unlike other fern species, Acrostichum species do not form sori on their reproductive leaves. Rather, sporangia are distributed over the entire abaxal surface of reproductive pinnae, lending them a felt-like texture. Additionally, not all pinnae on a frond are reproductive. in A. aureum, only 5 -8 pairs of pinnae at the tip of a frond are reproductive.
Mangrove Fern's Relationship with Humans
In Malaysia, Indonesia (Kalimantan, northern Sulawesi, Kangean and Timor) and the Philippines, young shoots of A. 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. A. aureum also has potential as an ornamental because of its handsome leathery leaves and the plant can be grown in pots.
Mangrove Fern habitat
This species is found in the intermediate estuarine zone in the high intertidal region. It is not restricted to mangrove systems and can grow in other areas in fresh water environments and in salt marshes. This is a species that is opportunistic and colonizes disturbed areas. It is fast growing, and very robust. It is a large herbaceous fern.